Tektronix 2215 Scope repair - Page 1
Forum section: electronics / repair

author: Vince
author_rank: Super Contributor
timestamp: June 01, 2018, 09:40:57 pm
content: Hello everyone.... oops, I did it again.... I bought yet another old CRT scope ! I just can't help, I kinda have a fetish for these thingsIt's a 2215 , will grow my little collection of Tek scopes. The problem is that as time passes, I happen to grow an interest for an ever growing number of different Tek scope models... and then there are the non-Tek scopes as well !The 2215 is a very, very basic scope, only 60 MHz and apart from a delayed time base and a cool 10 turn aluminium vernier to go with it, it doesn't have much going for it to be honest ! But I gradually find an interest in more and more of the 2000 series scopes, many of them have a little something that sets them apart in some way.As for the 2215 particularly, I recently learned on TekScope that it might well be the only Tek scope to feature an automatic brightness control circuitry. I always wondered why such a thing was not standard on just about every analog scope, since it's a real pain to have to constantly manually adjust the brightness knob every time you fiddle with the time base knob/sweep speed. So, I was curious to see for myself how this thing would work in practice, study the schematics/service manual for it, etc. From what I understand this feature was, in practice, more of a pain than an asset... probably why Tek dropped the idea... then a few years later, the first TDS all digital scopes arrived on the market, rendering this feature irrelevant anyway.So, when fate put a dirt cheap 2215 on my way... I just could not resist, bought it !Found one locally advertised at only 15 Euros ! Usually any 22XX scope here, goes for anywhere from 150 to 300... "as is", take it or leave it, no questions asked... So when I saw this 2215 for only 15 bucks, with a front panel dirty but other wise in excellent shape, with no scratches or dents or damaged or missing knobs... I e-mailed the seller the same day. Obviously the seller replied that he got a million calls and that he intended to pull the ad, the time to rethink pricing...He had absolutely zero clue what it was worth, nor how to operate it, hence why he sold it real cheap "untested, for parts or repair".I told him all about the scope, and in the end he agreed to sell it it to me rather than re-listing the item and sell it to someone else who no doubt would have been able to offer more money than I was willing to pay for such a humble and untested scope. We agreed on 40 Euros, much better than the original 15 he wanted for it, and muuuuuuuuuuuuuch better than 150/200/250 that I would normally have to pay ! So it was win-win...I received the scope yesterday, was so impatient, I started working on it just as soon. I plugged it to see what it would do, and not do...Pretty simple to describe the symptoms : "No Power" ... not a sausage ! LOLNot even a spurious attempt at coming to life, not even a split second blink of an LED, not a hissing from the SMPS, nothing. Just...... plain... cold... dead."Great" I thought, probably a power supply issue, gonna be an easy one ! Well, relatively easy at least. Last summer I had an in depth experience repairing the SMPS of another 2200 scope, my 2232, here :https://www.eevblog.com/forum/repair/tektronix-2232-scope-in-need-of-a-doctor/msg1226100/#msg1226100I assumed the 2215 might therefore have at least some similarity with the 2232 SMPS, so I cracked the think open to check the basics without the service manual just yet, just with my memories from the 2232 repair. Bad luck... when I pulled off the PSU metallic shield to expose its guts, it didn't look anything like my 2232So I looked the PSU schematics up in the manual... the circuitry looked familiar bar an important bit : the pre-regulator section was of a completely different design. The 2232 pre-regulator is implemented with a classical PWM chip driving a MOSFET... but that 2215 used a TRIAC !!! I thought these things were only good for domestic appliances and motor speed control for portable electric tools ! Never thought one would design a PSU for a precision/sensitive lab grade professional instrument, based on a TRIAC ! You learn something every day. The TRIAC was triggered by an SCR, itself driven by an opto-coupler.Then there is a little daughter board to handle current limiting."Great" I thought... something new to play with ! But ... no. When I opened the PSU, first thing I saw was a large board, horizontally mounted, covering all the area... board A18... and there is no such thing in the schematics... Then I pulled that board to look at the little current limit board that was supposed to be mounted underneath it. That's board A19.... but nowhere to be found on my scope ! Also, half of the stuff was missing from the main board/ A10... eh ?! Lots of unpopulated foot prints in the PSU area of the main board... hmmm...The manual can be downloaded from the Tek Wiki , around 22MB :http://w140.com/tek_2215_service.pdfFor those with a slow connection, I put together a mini-PDF gathering the various pages pertaining to the PSU, see attached below. 1,8MB, more manageable I guess. Oh no, it didn't go through, file size is limited to 1MB ... well sorry, I tried !Turns out I found all the answers to my dismay, when scrolling at the very bottom of the manual... turns out Tek made some heavy modifications/revision to the PSU at some point. Basically they dumped all that fancy TRIAC/SCR/opto-coupler/current limit board altogether, and retrofitted the previous design with the PWM circuitry. Of course that would mean re-spinning the main board, because the PSU is part of the main board... out of the question. So instead they put the PWM pre-regulator, and most of the PSU circuitry actually, on a daughter board, laying flat on top of the existing implementation. That's the one you can see on the first pictures, upside down, with the plastic transparent shield/guard. They simply unpopulated the main board, ran two wires to tap the mains pretty much straight from the mains switch, then at the output of the regulator, just ran two wires to the main board, going straight to the inverter.The beauty of it is that the access to components is now 10 times better/easier than it was in my 2232 ! On the 2215 that regulator board is a the very top of the chassis, every thing is readily accessible for you to closely look at , and probe. Plus, the wires are long enough that you can flip the board upside down and access the component side as well, while the scope is running ! What a luxury. This will no doubt make trouble-shooting so much more pleasurable...Also, it is now dead easy to break the link between the regulator and the inverter, so you can bypass the former and feed the latter directly, to figure out quickly if the fault comes from the regulator, or the inverter/downstream parts of the scope : the wires are already there, just unplug the regulator board and tap those wires !So I did just that. First I measured the output voltage of the regulator, while loaded... got around 1 Volt , weird. I would expect either nominal voltage, or zero if the PWM chip cut power due to a short/overload situation... Having "some voltage" just didn't make a lot of sense to me.Still, to make sure it was not the inverter/scope loading abnormally the regulator, I disconnected the regulator output wires and measured again its output voltage.... now 13 Volts or so ! Instead of around 40V. 30% there, getting better by the minute !Still didn't quite make sense. But at least the regulator was not loaded, so had no excuse, hence I declared the regulator faulty, not the scope itself. As a quick sanity check, I powered the inverter directly with the bench power supply, set to slightly around 40V.Success ! Houston, we have a trace ! Winner winner chicken dinner !I then spent 5 minutes checking the basic features of the scope to see what works and what does not... behaves quite weirdly. I think 30% of it is definitely due to really dirty switches and knobs that need a good dose of contact cleaner. 30% might be due to that auto brightness feature playing up and interacting in some way with the trace. 30% of it might come from a possible slight under voltage condition throughout the scope, as I set the bench power supply only roughly, as at the time I did the experiment I had not yet found out that the service manual did cover this regulator board... so I was only doing it from the memories of working on my 2232 SMPS.So that's where I am at at the moment !1) Narrowed it down to the regulator board, now need to trouble shoot this board.2) Possibility of secondary/minor faults further down the line, but maybe not. Might just fix itself once the regulator is back up to specs.Well actually I already started to do some basic trouble shooting on the regulator board last evening, was real tired and late for bed, but did some quick tests none the less (without the schematics at the time):- Visual inspection revealed nothing. No damaged components, no burn marks on the PCB, no fried components... it all looks good.Only thing that caught my eye, are the leads of a couple small Zener diodes : they are completely black, like they were painted. But it does not look like they overheated... their bodies and the surroundings show no sign of overload/overheat what so ever. It basically looks like the leads of these Zener diodes were painted black at the factory ! Can't figure out why though... anyone ever seen this before ?? I am curious.- Checked all the input protection and filtering section : all good, mains goes through. Full wave bridge rectifier good too. Mains filter cap good (enough, don't have an ESR meter just yet) : DMM shows a steady 320 DC Volts across it and no AC component on top of it. That rectified mains does make it to the drain of the FET. Did a quick diode test on the FET : it is not shorted... I kinda expected that, otherwise the regulator board would be in a pretty sad shape ! LOL I should know because this is precisely what happened to my 2232 ! Not a pretty sight indeed..... no such thing on this 2215.So maybe the FET is faulty but opened (is this is a possible failure mode for a FET ? .... ), or the surrounding circuitry fails to drive its gate.I need to investigate this board closer now, and fire up a scope to look at some waveforms here and there... 11h30 PM here, getting tired.. I will start work on it seriously tomorrow....Anyway, that was for the introduction !Now let's work this baby until it behaves !

author: tautech
author_rank: Super Contributor
timestamp: June 01, 2018, 10:03:07 pm
content: Cool Vince, and great write up thus far.Looking forward to following this.Off to study the schematics........Be careful with this one Vince, the pre-reg calls for use of an isolation transformer but if you haven't got one a differential probe will be even safer.Luckily you have some listed DC values to check against first in some effort to zero in on the faulty part.Next I'd be checking the all the smaller caps then focus on active components if the resistors test near enough in circuit.

author: Vince
author_rank: Super Contributor
timestamp: June 02, 2018, 12:52:54 pm
content: Hi Tautech, thanks for stopping by !Don't have a differential probe just yet, too expensive (might go for the "EEVBLog" rebranded probe, since I understand it's good quality and excellent value for money).However I do have an isolation transformer, rated 100VA, will be plenty enough for this simple/low power scope. Worked just fine when I troubleshot the SMPS of my 2232... yeah you better watch what you are doing when hooking another scope to the primary side of the SMPS, as it's not referenced to the chassis like the secondary side/scope is.I have not yet started work on that regulator board, however some additional thoughts came to me :- As I said the rectified mains does make it to the drain of the FET... there is an important and very happy conclusion that one can draw from this : it means that the only painful/proprietary part on that board, the switching coil/transformer, is NOT blown (like it was on my 2232 due to the FET shorting). So now I already know that whatever is wrong with this regulator board, it will be a cheap and readily available part ! So this thing CAN be repaired easily I would think !- I might have a lead/clue about the 13+ Volts I measured at the output of the regulator, while not loaded. If you read the manual and look at the schematics, 13/14 Volts is the voltage that the circuitry creates at power up, to supply power to the PWM chip. Once this voltage is reached, the PWM chip is able to operate, ans starts acting on the FET's gate to regulate the output voltage. So it's possible that even though the FET is constantly open/not regulating anything, the circuitry, the way it is designed, all by itself, maintains a 13+ Volts level in there. So this probably means that :A) The circuitry that powers the PWM chip, is fineB) The FET is just fine.. just not being driven.The fact that the output drops to next to zero, 1 Volt or so, when it is loaded by the inverter, could be explained because the circuitry that produces the 13+ Volts to power the PWM chip.. well is only designed to spit out a very low current, just enough to power the chip ! To start with, that circuitry is fed by the rectified mains, 320Vdc via a 150K resistor ! So that's 2mA max, not much at all. So if you hook it up to the inverter, which draws around 750mA, there is no way it can keep up ! So the voltages I measured suddenly make perfect sense in the end...So from all this, my first guess is that the problem is either the PWM chip not working, or it works but it fails to drive the gate because the gate driver (external/glue circuitry) is not working.That will be my starting point...Also, it is now very probable that I had indeed a slight under voltage condition in the scope when I tested it and witnessed weird effects here and there : as can be seen in the picture, I set the bench power supply to about 40,5V. Now after the fact, I read the manual and it states that the PWM chip regulates at 43V, so I was 2,5 Volts short. Given that the inverter does not regulate anything (the reference -8,6 Volts can be adjusted, but it is not regulated. So for a given setting of that trimmer, I think that a lower input voltage/regulator output, will automatically lower the voltage of all the power rails... ).So here again there is hope that a properly working regulator will fix some of the issues I noticed during my brief test ride.

author: Vince
author_rank: Super Contributor
timestamp: June 02, 2018, 01:40:13 pm
content: Oh, just got a message from the seller. Says the scope belonged to his dad who recently passed away. He is delighted that I managed to fix it and that the instrument will enjoy a second chance/new life instead of being dismantled for parts, or just scrapped altogether.That's heart warmingI now have a duty to finish the repair of this scope, give it a good clean, and keep it with me rather than reselling it to make some profit out of it, which had never been my intention to begin with anyhow...

author: oldway
author_rank: Super Contributor
timestamp: June 02, 2018, 01:53:53 pm
content: https://www.eevblog.com/forum/repair/help-with-tektronix-2213-power-supply/msg1530746/#msg1530746Your posts are too long for those who are not native English speaking.

author: Vince
author_rank: Super Contributor
timestamp: June 02, 2018, 03:42:22 pm
content: Hi Oldway,Thanks for the link. Looks like the OP, unlike me, has indeed the TRIAC version of the regulator, and is resorting to using brute force to get it working, replacing every component 'til it works, rather than trying to diagnose/locate the fault. I guess we can't always afford the "luxury" of taking the time to properly trouble shoot a board. As for me the trouble shooting / detective work is precisely what I am after, the successful repair is only a secondary goal, the icing on the cake so to speak. What matters most to me, is the journey, not the destination per se.I am really sorry if you don't like my long messages, though I understand/remember from previous contributions of yours on my past topics, that you are fluent yourself. I guess you speak for others then ?I would argue the following, if you allow me :1) I am hardly a native English speaker myself, being French, which are universally recognized as probably the people with the least capabilities when it comes to grasping the English language, that the earth has ever carried. So if I can (about....) do it, anyone can do it, for sure2) How did I learn English ? By reading poorly written on liners on forums, comments on Youtube or Twitter or such atrocities ?! Definitely not. The only way to learn English is to read hundreds and hundreds of pages written by actual native English people, who master their own language decently. Read technical papers, read the news papers, listen to some BBC podcast programs in the UK, read, read read.. The more you read, the better you get, just like one learns his mother tongue effortlessly simply by listening to it all day long. It progressively but surely makes its way into your brain.3) Learning English is much more enjoyable/easier if the material relates to something you are interested in : electronics here. This forum is an opportunity to learn English the easy way. I would not want to learn English by digesting piles of big books filled with law articles, for example...4) Reasonably, if one comes to an English speaking forum, he has to be prepared to make the effort to keep up, rather than expect the whole world to accommodate for the lowest denominator. If I had to go to a Russian forum to say, seek info on an old nixie tube or whatever, I would hardly expect our Russian friends to post on liners just because some French chap decided to get on board.5) Don't get me wrong : this post is long because it originated from me, and was meant to detail/introduce this repair, tell the "story". Subsequent messages don't necessarily have to be as long...However If I was REPLYING to someone, who clearly was not fluent and was clearly looking for a quick answer to fix his problem at hand, then yes of course I would make the effort to use simple words, short sentences, and be as synthetic as can be, to help him. But here on this topic, I was not replying to anyone, I was creating my own stuff.. so I dare to think that one is free to express himself the way he sees fit at a given time.. just like anyone is free not to read me, or not reply to me if he gets bored and falls asleep before he could even make it to the end of the post. Every one is different, people just pick what they like and discard the rest, it's only natural...6) In my repair topics, the whole point is to share my thoughts/trouble shooting process, since this is what I enjoy, and this is where I think the value is. If all I wanted was to fix this scope, I would not even bother posting on this forum. I would just fix it and not post anything about it... but that would suck. I like and enjoy reading about others repair stories, seeing the guts of a piece of gear I have not seen before... so logically, I like to contribute myself, give a little something back, share repairs when I have the opportunity to do so.What would be the point of me posting a one liner like: "Hi fixed 2215 woz preregulator replaced a few random caps and that deed it, cool bro ! ". How useful would that be ? Both in terms of learning something on the technical side, or in terms of improving one's English skills, for the many foreign people like me ?7) Experience on countless forums shows that I am the only one on earth to bother writing such long/detailed messages on forums. So really, not reading my posts will hardly harm anyone, not a big loss... 0.00000000000001 % of the total amount of messages on here.8 ) What about Dave's EEVBlog ? He speaks at the speed of light, and seemingly without ever taking the time to breathe, for sometimes more than one hour. Should he make 30 seconds videos, speak like he would to a 2 year old, and use only 10 words of vocabulary, just because non native might (and do) watch his YT channel ? No, I surely don't expect him to do that, nor would I ever want him to ! Just the opposite : The more he speaks, the better I get at understanding him, the more new expressions I get to learn. The richest/more varied the vocabulary, the better ! Same goes for any other video blog of course. The brain is a machine that needs to be trained : you need to feed it with material or it will starve and progressively but surely....perish.9) ... no there is no #9 !Somehow I felt the need to justify myself, God knows why... maybe because you used a big "thumbs down" icon, that made me think you were really extremely upset, which I felt was ungrounded.Next time someone "complains" about my long messages... I will just link to the present post , will save me the hassle of explaining the same things over and over again.I apologize to every reader (ie, the very few who can cope with my writing !) for this off-topic mini-essai... back to the repair now, we got a scope to fix !

author: oldway
author_rank: Super Contributor
timestamp: June 02, 2018, 04:29:38 pm
content: Sorry, too long reply for me....I'am interested in solving technical problems, not to learn English ....I already speak and write 3 other languages, I think it's enough.

author: Simon
author_rank: Unknown
timestamp: June 03, 2018, 03:25:48 pm
content: Quote from: oldway on June 02, 2018, 04:29:38 pmThen go away and don't come back to this thread. No one has to meet YOUR expectations!I am reopening this thread and any more off topic crap will get the offenders banned. We seem to have far too many people here that think they can make their own rules up.

author: floobydust
author_rank: Super Contributor
timestamp: June 03, 2018, 07:01:42 pm
content: We had dozens of 2215's in the lab as workhorses when they first came out in the 1980's and at first I loved them then it turned to swearing and cussing.With even a few years age, the trigger section degraded somehow and the scopes became finicky, they would not trigger reliably on simple waveforms.Note theTek 2215 Service Manualhas many ECO updates (last pages), including to the trigger circuit.I wonder if Tek rushed to get these out to market. It could be Trigger adjustment trimpots R482, or R511 or I faintly recall it was varactor diodes aging but it doesn't make sense they (varactor) was used for this purpose.How do you find the scope performs compared to others in your collection? I was going to get one but not sure if a 475 kicks butt, to go back a generation.

author: Vince
author_rank: Super Contributor
timestamp: June 03, 2018, 08:29:42 pm
content: Alright. Spent some more time on the pre-reg board. I did all the checking I could do with the DMM, before I resort to firing up a scope to check waveform.Checked all the passives, lifting a leg here and there when needed, to get a reliable measurement.- All small signal transistors check OK (I pulled them to be 100% sure...)- All 3 electrolytic caps measure fine and don't leak, but no idea about ESR since I don't an ESR meter just yet. Soon hopefully, though.However for the kind of symptoms I see, I don't see how a high ESR could explain it. So I will replace them for good measure and preventative maintenance, because they are bound to go bad later on (scope is 36 year old already...), but I don't expect it would make any difference for the problem at hand.- The 4 tiny caps around the PWM chip, come in a funky packages. 3 of them come in dipped bright green axial packages, and two come in a transparent glass package with red terminals, making them look disturbingly like an old Germanium diode !However I was not too shocked, because I learned about their existence of such packages for caps, from a gray beard who designed crystal oscillator prototypes in the 70's. These glass dielectric caps had the advantage of very high temperature stability, IIRC, which was critical in getting the oscillator to be as accurate/stable as possible, which was his goal back then.Anyway one of these green caps broke in two when I lifted one of its legs... was gentle I swear. So I guess this cap was just waiting to fail anyway. That was C929. Then the two remaining green caps (C925 and C920) don't instill a lot of confidence either : I lifted a leg on both them, yet the DMM wouldn't register anything, display was stuck to 00.00nF, didn't budge. That means these caps are.. open. So all of these green caps will be replaced.Trap : in the pictures, you can see not 3 but 4 of these small green packages... one of them is NOT a cap, but a precision/ 1% resistor ! Go figure... never seen a resistor packages like this. Also, the accompanying resistor (other leg of the voltage divided that sets the output voltage, R921/R922), comes in a "normal package. So it's not consistent...- R937 reads a bit high at 8.75K for a nominal 8.3K 5%. However I do'nt think it matters at all, given it's purpose on the board. It's in parallel with the filter cap on the output of the regulator. Not even sure what it's for... The output being at 43V, is above the usual "safety" level, 24V IIRC (my meter gives a warning above 24V anyway). So maybe the resistor is meant as a bleed resistor for the capacitor. However I don't see the point of it since the regulator board is supposed to be permanently wired to the inverter, which draws 750mA or so... which would bleed that capacitor real quick anyway...However if Tek really cared about safety and bleeding capacitors... I would have found it much more important and logical, to bleed the high voltage cap that rectifies the mains : 320Vdc ! But they is no bleeder there... I timed it, takes quite some time for the cap to discharge, over 30s.Other hypothesis : that resistor is there to ensure a minimal load on the regulator, for it to work properly. That wouldn't be uncommon. However, again... the inverter it supplies is plenty enough of a load. So, this dummy load would be of any use only when a service tech disconnects the inverter to trouble shoot the SMPS... just like what I am doing right now. IF so.. how thoughtful from you , Tek ! Thank you.- R911 reads really too high : 180K for a nominal 150K. Sure it's not a precision item, just the common 5% type. However even at 5%, the maximum value would be 157,5K ... and I measured like 180K. I am not too sure what kind of impact that would have on my symptoms though, but at least it's worth keep it in mind... Oh, this resistor as you can see is the beefy 1Watt thing that feeds the 320Vdc to the circuitry that powers the PWM chip.- Checked the switching coil/transformer / T933. As I suspected, and hoped, it is just fine, hooray. All 4 coils in it, are neither open nor shorted. They all read plausible values, in tune with what I measured on the similar tranny in my 2232 scope. So that's a big relied indeed !After I had checked all that, I resoldered all the legs I had lifted, reflowed a few solder joints for good measure, then powered the thing back up to see if it somehow made any difference. Did not. As I expected, all the green caps, which I removed because either broken or reading open, didn't impact the symptoms the slightest bit : we still have 13+ on the output, and only 2,8V for the PWM chip power supply instead of 14V...So I then removed the PWM chip itself (and soldered a chip socket in its place while I was at it), just to see if it might be defective and load it's power supply too much, to the point of dropping it from 14V down to the 2,8V I was seeing. Without the chip, the supply goes back to 10,7 V or so, much better, but still not the expected 14V ! But this time the PWM chip can't be blamed.. so the problem must lie elsewhere... in the circuitry that's in charge of generating that 14V to begin with. I highlighted that circuitry in the schematics below. Also attached, the 3 pages of text that describe the operation of the pre-reg, including this little circuitry.Basically you have C913, 100uf electrolytic, which powers up the PWM chip. At power up, it progressively gets charged by the rectified mains, through R911, that 1W 150K resistor that I just discussed above, which reads 180K instead of 150K...Once the voltage across that cap reached 14V, the circuitry then regulates it at this value (by means of transistor Q917 and a Zener diode VR917) and sends this juice to the PWM chip power pin (#12) using transistor Q915.So, I measured the voltage drop across the Zener diode, which is a 6,2V one... got 2+ volts IIRC, don't quote me on this, which didn't make sense to me.The Zener tested fine with the DMM, in the forward direction. Obviously I could not test it in reverse bias.So since I was still looking for leads on this repair... I bit the bullet and pulled that Zener so I can test/characterize it properly, on a bread board.10K in series, reversed biased of course, then ramped up the voltage progressively with the bench power supply. What I witnessed was most strange.. the Zener is definitely bad, and sure enough the circuitry can't work properly with this things in it !Now I have no particular knowledge or possible failure modes for Zener diodes, other that that common to any PN junction : either shorted or open...So this is what happened on the bread board... two problems at once :1) It's a 6,2V Zener, but somehow the "knee" drifted dramatically : it starts to conduct at a much lower voltage : 2Volts or there about !2) Once it starts conducting, hence we have passed the knee... there is another problem : it still does not regulate anything : the voltage across it keeps rising and rising, somewhat linearly. In other words, it's dynamic impedance has increased dramatically ! It does not "regulate" anything anymore.So that was quite interesting to me, this scope repair was worth doing for seeing/learning these failure modes in Zener diodes...I had a few Zener diodes in my drawers (sadly no 6,2V nor any values that I could combine/put in series to add up to 6,2V), new, but about the same age as the scope or almost. 25 years at the very least, or shy of 30.So I was curious to test them all, see if I just got unlucky on the Tek scope, or if there was a pattern there...I was not disappointed : had of old new Zener diodes showed the exact same issues !!!So there you go : it's definitely not uncommon, it was not just bad luck.. this a definite failure mode for these things !Not sure how relevant it is, but I also noticed something : out of all my new Zener diodes, only the low voltage ones were affected. Those rated at under 10V.I had 3,3V ones, and 4,7V. Then I had 12V, 15V and 25V.Might just be a coincidence.. but maybe not, because there is a pattern : I had around half a dozen diodes of each value. I tested 100% of them. I noticed that 100% of the low voltage showed this issue, and absolutely NONE of the "high" voltage ones did.To finish up with the Zener : I figured the black coating on their leads : it's a fine oxidization layer, easily scrapped off. Only the Zener diodes on this board have this... I guess their leads must be made from a different material than all the other components...So with a 6,2V Zener that starts conducting at 2V or about, and which is unable to regulate anything, no wonder it doesn't work.There is still a bit of mystery as to how I can measure 13+ Volts at the output of the regulator, when the PWM circuitry puts out on ly 10+ V ....Maybe the tow voltage levels are unrelated then. The only path I see for juice to get to the output while bypassing the PWM circuitry, is via the FET.. so maybe it conducted a little bit even though it is not driven. So might still be faulty in some way, just maybe. I will pull it to see if the output drops to zero. Ought to.OK so that's it for today.I will now order a few components to be able to go further :- Zener diode, hoping it would cure the problem- Replacements for all the 3 tiny green caps that either open bad or broken in two...- New electrolytic caps, for preventative maintenance- New R911, 150K 1W high voltage resistor in case it reading 20% too high maybe part of the problem, along with the Zener.- And just in case : a new PWM chip and FET, so I don't have to pay shipping twice just to get hose if I do happen to need them.Sadly the parts list, maybe because it's related to a revision change and not the main/original parts list... does not give enough technical detail to be able to order a replacement part : just says "N-Channel MOSFET" .. great, how helpful ! So I can't check whether the FET in place is the correct one (might have been replaced and be part of the problem..). But well, I will just go buy the info in my 2232 part list. IIRC the FET is not critical, back then we found several possible modern replacement. Hell I might still have some spare/new FET's from that 2232 repair, that I could re-use in that 2215... need to check my "archive" box...- Might also recap the main board, to be consistent : the inverter and the secondaries.Oh ! Forgot a nice thing : the non-working delayed time base I noticed during my quick test ride... works just fine in fact : it's just that always.... I forgot that to for ti ti work/display the trace, you need to get to the "B Trigger level" knob in the upper right corner of the front panel, and cranck it all the way CW, in the "run only after daily" position... Works much better now ! Operator error, hum hum..Some attachments and off to bed :- Principle of operation of that regulator board- Board layout of the board- Overall schematic for the SMPS, which of course includes the regulator board, which occupies half of the schematic just by itself...- Annotated Schematic of the regulator, highlighting my main focus : the circuitry responsible for providing the 14V to the PWM chip.. which we need to get working.

author: Vince
author_rank: Super Contributor
timestamp: June 03, 2018, 08:30:30 pm
content: ...

author: Vince
author_rank: Super Contributor
timestamp: June 03, 2018, 08:52:10 pm
content: Quote from: floobydust on June 03, 2018, 07:01:42 pmHi FloobyDust,Thanks for sharing your experience with these things... not too promising it seems ! LOLI will keep your remarks in mind when I get to test it properly...For now it's still in pieces so it's early to give any opinion on the thing. That said, even assuming I could get it to perform superbly, then the cold fact remain that it is a very basic, very low end scope indeed... you can't change that. Based on this alone, I can safely that my 2232 is vastly superior to this 2215, in every department... 100MHz BW vs 60MHz for the 2215, storage mode, cursors, XY plotter output, GPIB connectivity.. My 2232 is my main scope. Then if I compare that 2215 to my TDS 544A of course it's not fair for the 2215 ;-)However I could make a more meaningful comparison, that would be with my old Hameg HM604. Again an old, basic analog scope, same 60MHz.In this case, I would choose the 2215 over the Hameg any day. The Tek is just in another league. Everything looks and feels more refined, and it just looks 10 times better as well, though this is obviously of no technical relevance, and entirely subjective ;-)Now compared to the 475 you envision.. well I have no experience of this scope, so not much qualified. However from what I understand here and there, they were very dependable scopes, well built, everybody loves them... Meant as a service scope so it's very compact, however they crammed as much performance and features as could into these scopes. So unlike the 2215 which was meant to be, from the get go, an extremely basic and low spec scope... the 475 was just the opposite : a quality and high spec scope. The BW alone speaks for itself : 200MHz and 250 for the 'A' revision.. vs 60 for the 2215. Right there, they are not at all in the same league !So I would say... yeah, get a 475 any day over a 2215 ! I will repair my 2215, but sure as hell I will get a 475 as well as soon as money permits !You could ask all the gray beards for confirmation on the TekScope forum, but I don't think I am too far off....

author: tautech
author_rank: Super Contributor
timestamp: June 03, 2018, 10:02:23 pm
content: WRT the FET, a Tek cross ref will save your bacon, maybe this one:http://www.sphere.bc.ca/test/tekequiv.htmlAt the bottom right of the page is another more comprehensive one Sphere ask not to be linked.Good progress Vince, I'll review it in detail today so get some sleep buddy.R911 drifted high mightn't let the controller kick off as SMPS IC's usually have UVLO.

author: floobydust
author_rank: Super Contributor
timestamp: June 04, 2018, 08:16:26 pm
content: For the mains SMPS MOSFET, Tek changed to a different part in the 2213,2215,2235,2236. Depending on the scope's serial number, see parts replacement kit050-2242-03151-1152-00 replaced by 151-1245-00 using the parts kit. Also the main DC-DC and OVP SCR were updated, bunch of resistors added.151-1152-00 IRF820/MTP475 500V 3.0 ohm 2.5A 360pF151-1245-00 MTP6N60E (was MTP6N55) 600V 1.2 ohm 6.0A 1,500pFThe MTP mosfets are obsolete and what I could find in stock at Digikey replacing 151-1245-00 looks like:IRFBC40600V 1.2 ohm 6.5A 1,300pF 50WSTP9NM60N650V 0.75 ohm 6.5A 452pF 70WSTB6NK60Z 600V 1.2 ohm 6A 905pF (has internal protection zeners) but obsolete partSome relevance:https://www.eevblog.com/forum/repair/suddenly-unable-to-start-tektronix-2235-(analog)-oscilloscope/msg1285884/#msg1285884

author: Vince
author_rank: Super Contributor
timestamp: June 04, 2018, 08:57:49 pm
content: Thanks for all the good info Floobydust ! That should sort me outIRF820 ? This is what's on my regulator board.... so it was original then. Boy 3ohm Rdson, that's truly horrible... yes will definitely replace it with a better part. I might have some left from my 2232 SMPS repair, need to check...The SCR is fine on my 2215, I mean it's not shorted...Yes they definitely modified the SCR part of the schematic... on my 2232 the SCR is shorting the rail solid... but on the 2215 I see they added a beefy 3ohm resistor in series with the SCR.I Paid a visit to my local electronics shop after work, picked a few components... he didn't have the tiny dipped ceramic caps (too "exotic".. will need to order them from Farnell or whatever), so I won't be able to get the PWM chip to work.However of course he had a 6,2V Zener diode and a 150K 1W resistor, and the two electrolytic filter caps for the PWM chip and regulator output.... so hopefully I will be able to fix the 14V circuitry that powers the PWM chip, that's the most important !But it's late and I am tired.... so will play with that tomorrow hopefully !

author: Vince
author_rank: Super Contributor
timestamp: June 05, 2018, 10:26:22 pm
content: SUCCESS !Just back from spending a couple hours on the thing. I first replaced the Zener. Bought two of them just in case. Now being a tad paranoid about Zener diodes, I first proceeded to test them both on the breadboard... and well, again was interesting ! They were twin sisters, coming from the same reel, adjacent to each other. Yet... somehow one was distinctly performing better than the other one ! One was working just fine, with a sharp "knee", quite accurate at 6,2V despite the 5% tolerance which would allow it to vary quite wildly, from 5,9V to 6,5V roughly. Also, the dynamic impedance was very low, it "regulated" really well. OTOH, the other one had a rather "fuzzy" knee, and had a noticeably higher dynamic impedance. No need for a curve tracer to figure it out, it's easy to spot just by looking at the DMM...So needless to say, I picked the best of the two.As I hoped, it fixed it !I now do get the expected 6,2V drop across the Zener, and the circuitry now produces 15V, much better !Supposed to be 14 but hey, still happy.Then, just in case it might bring it down to 14V, or make any difference, I proceeded to replace R911, the beefy 1W 150K resistor that measured 180K....I bought a 2W instead (I like safety margins in high voltage stuff.... ).. and turned out it has the exact same dimensions ! Twice the power, but same size, hum...The original resistor is old tech as you can see. Brown body and perfectly cylindrical shape, the kind you found routinely in old tube based gear... so maybe this type was not capable of dissipating as much power as the more modern kind, don't know.Anyway, not sure why just yet, but replacing that resistor DID make a difference ! However not in the direction I would have liked : instead of lowering the voltage to bring it back closer to the desired 14V.... it threw it even farther : now reading 16,8Volts !Still... not too fussed about it : the PWM chip doesn't really care, and it's got its own 5V reference anyway...Then I replaced the two LV decoupling caps : C913 (PWM supply) and C934 (regulator output). Somehow that too made a (slight) difference : PWM voltage dropped by 0.2V. Go figure. Notice just how much smaller the new caps are ! Yeah I know, modern caps are always much smaller than their old counterparts but... these are really, really much smaller, had to measure them twice with the DMM just to convince myself... They are about a third of the volume of the old ones... even though I increased the voltage rating on both of them !Yes... Tek really didn't give them much head room ! C913 is for the PWM chip, hence sees 14V. They used a 25V cap. OK, that's about reasonable on this one, just. Still, I bought a 35V one, because price is so ridiculously low on these, and it would still be smaller than the old one, so no problem fitting it to the board.Then there is C934. It sees 43V, the output voltage of the regulator.. .and they used a 50V rated cap ! Eh ?!I bought a 63V one...Both OEM caps were Nichicon.. killed me to replace them with crappy brands... but well, that was just for test purposes. I will later place an order on-line from Farnell or whatever, and therefore be able to choose a good brand. Oh, and Tek used 85°C caps as well ! And the scope does NOT even have a cooling fan ! Grrr...Was looking good, so I thought what the heck, let's plug the PWM chip into its socket, and see what we get ! Of course with a missing/broken ceramic cap, and 2 dubious ones that look like they are open circuit... the chip should not be able to operate. However... I could at least, probably, see if its internal 5V reference was working... and it was : reading 4,98V , a good start, it's alive !Then looking more closely at the schematic, you realize that the broken/missing cap, is C929 : it's across the two inputs of the current limit comparator. I thought that must be to reduce signal noise. Useful, but not vital... chip should still be able to operate without it. You bet it does !!!When I powered it, I heard the typical "wizzz" noise coming from the board ! Hummm I thought, this thing sounds like it's alive !I rushed to check the output voltage : 43,3Volts (for a nominal 43V) : VICTORY !!!Then checked the PWM chip power supply : down to 13V now, woohoo !!! So the 16,5V I got initially, was nothing to worry about... as soon as it's loaded when then PWM chip is in place, it goes back down !13.0V is not the 13,9V indicated in the schematic.. but again I think it's just fine...So... the two ceramic caps that I thought were open circuit.... maybe they aren't after all ? Driving me mad... the DMM was not registering anything, even though it had enough resolution to measure them ! Worse case, may be C925 could indeed be defective and it would not show because its role is not vital : from the schematic it looks like its purpose is to reduce noise on the output, by lowering the output voltage/gain for high-frequency signals.However C920 can't possibly be faulty as it determines the oscillator frequency !Had a quick check with the DMM : PWM output is about 35kHz, manual states 40kHz, ball park...So... seeing as the regulator board was working.. at least well enough for test purposes, I then hooked it to the inverter/scope. Would the scope fly with its own wings now ? Sure it does ! And now the SMPS makes this horrible, high pitched pulsating noise that would make many suicide... and which is unfortunately typical of any and all 2200 scope, arf... My 2232 does it too, takes 15+ minutes for it to progressively quiet down. On TekScope this very subject has been discussed at length.. many theories have been proposed as to this noise, many experiments were done... in the end, as far as I remember, there is no definitive answer, never mind a sure fix. Sadly. I guess as I get older/deaf, I won't even be able to hear such a high pitched noise, so I won't care anymore !But until then.. it kinda drives me nuts.So, yes, the scope now powers up and runs fine... I am a happy camperWith the inverter hooked up, I measured again the output voltage of the regulator : yep, when loaded, it drops a bit, from 43,3V down to 43,15V .Pretty much spot on.So I call this a fix ! That was a quick one, I got lucky !All fixed for the price of a 10 cents Zener diode, how cool is that.Now I will order decent brand caps, and recap the whole scope : secondary side of the SMPS, and also I spotted a few electrolytics on the sweep board as well. Will inspect all the boards to find them all, there will be no mercy !Once this is done, and once I have cleaned all the dirty switches... I think we can then test it thoroughly and see what issues might remain.I can already see one... which we can probably spot on the pictures too : when I enable the delayed time base, there is a problem with the brightness of the trace : right after the part of the trace which is highlighted, there is "dark" spot where the trace becomes invisible. It's about the same width as the width of the highlighted part. Must be a lead as to what is wrong. Will need to check how the delayed time base works. Maybe a dodgy cap is creating some lag/ghost effect that creates this trailing effect. So might cure itself once I have recapped the whole scope... hence why I won't bother investigate this issue for the time being...Anyway, that's my second 2200 SMPS repair... I am starting to get the hang of these things, might buy another one if I can find a cheap one again (unlikely...) !So, next : buy a bunch of caps to recap the whole scope, clean switches, and test the thing again.See you in a bit then !Bed time again...

author: tautech
author_rank: Super Contributor
timestamp: June 05, 2018, 11:08:13 pm
content: Cool Vince, well done and thanks as always for writing it up like you do.Those old carbon resistor can drift like hell and any that are suffering any load, it's wise to replace them.WRT the caps, both ceramic and polarized in the SMPS you can be damn sure Tek knew what they were doing to include them and probably for a little bit of trouble you might be wise to replace all in the PSU maybe with the exception of the primary side bulk cap if measured capacitance is still close to spec'ed value.There may be different ESR specs for modern caps as opposed to what Tek used and little things like that could be responsible for PSU whine as it's essentially operating with parts outside the original design. Food for thought maybe.I'm sure the whine could be addressed with some rework of the SMPS values to get the transformer operating in a happier place. You'd probably need a good current probe to do so and do some tweaks to the MOSFET ON time (less).Did the display show any problems when run on external PSU ?If you use Horz Pos, does the dim region move ?

author: Vince
author_rank: Super Contributor
timestamp: June 06, 2018, 08:18:51 pm
content: [Just proof read my previous message, corrected a million and one typos. Should make for a smoother ride now... ]Hi Tautech,Quote from: tautech on June 05, 2018, 11:08:13 pmYep sure, that was on the cards. I am not taking any chances...I notice that on the secondary side of the SMPS, the caps are really old "Mallory" branded caps, half a dozen of them, and that two of them have already been replaced from what I can see ! No doubt about that. They can be seen in my first round of pictures in my original post. So if only two of them were changed, it means they must have been bad to the point of leaving no choice, so they must have been reallllly really bad ! So, all the other Mallory still in place are logically ticking time bombs... will replace all of these of course.QuoteYes I thought likewise. This mains filter cap is kinda special... from what I understand and witnessed on my old Tektronix 317 tube scope, and many reports on TekScope, these caps Tek used were astonishingly reliable/long lasting. My 317 is from 1959 and the LV power supplies are still dead on, and ripple free. I just could not believe it.So if I were to replace this special purpose cap with a generic 450V low ESR electrolytic, I might well be doing more harm than good, trading a proven and purpose designed cap, with an unproven one... Not a good move I feel. That cap measures at 91uF for a nominal 75uF and +50% tolerance ! So in other words, it's still welllll within tolerance...Will only replace it if there is a definite evidence that it's faulty and causing trouble.QuoteYes. That said my 2232 made that noise even before I repaired it... I am fairly sure ?! So if ESR related it is, then even non-modified scopes don't have the appropriate ESR. New caps because they are designed this way, and the old original caps because their ESR increased of the years... different cause, same end result...QuoteI will try to dig out that topic from TekScope. The idea back then was similar to what you suggest. IIRC the OP was suggested to add C and R trimmers to the PWM oscillator, so as to be able to fine tune it, in a hope that one could find a sweet spot where the transformer would not resonate with anything, and just be silent.QuoteYeah a current probe is on my list of things to get... I recently found a YT video about a nice one at a decent price, 450 bucks or something, going right down to DC, and up to 100kHz of bandwidth.Now I think of it ! This could be an interesting and useful way to use this little 2215 scope ! I mean, let's be honest, I have zero use for it, my 2232 is my main scope and is much better. HOWEVER, the SMPS in the 2215 is WAY easier to work on, compared to the one in the 2232. Also, since I don't need the 2215, I don't have any problem having it non working, in pieces, for months and months... I just don't care.So... I think I could use this 2215 as a test bed to work on this whine issue !When I power the inverter from the bench power supply, the scope is perfectly silent. So the whine must indeed be coming from the regulator board/PWM tranny. And since this board on the 2215 is standalone, very low density and can be accessed and probed with so much ease.... it is the ideal candidate ! Then, once/if I can manage to make the regulator quiet, I could then apply the remedy to my 2232 quickly, meaning no significant down time at all !And then I could apply the recipe to any and all 2200 scope I might purchase in the future....Yes I like the idea ! Playing with a current probe, watching waveforms, and I could even record the audio "track" from the transformer, as there is always a distinct pattern to it, which evolves as the scope warms up. It also reflects on the signal trace on the CRT, which "dances"/wobbles according to the pitch of the whine. The lower the pitch, the higher the amplitude of the wobble.I also have a spare tranny from my 2232 repair. I could also conduct tests on it : feed it with a range of frequencies and wave forms/shapes to try and see what "triggers" it.Yeah could make for an interesting little project, and hopefully a very useful one if it eventually succeeds and leads to a fix we can apply to all those 2200 scope, which are still plentiful on the market !QuoteHmmm, good point. Just tried it. Running the inverter from the bench power supply doesn't happen to make the slightest of a difference. 100% similar outcome.QuoteYes it does. It "follows" the highlighted portion of the trace invariably, sticks to it no matter what.Same thing if I fiddle with the delay vernier : if I move the highlighted portion of the trace from left to right, again the dark/dim spot on the right of it, follows suit.Also worth noting : the dim area does not affect the entire height of the screen, so I guess it's safe to say the issue is not related to the auto-brightness feature possibly playing up, but rather located solely to the delayed time base section of the scope. Whatever circuitry is responsible for handling the brightness of the delayed portion of the trace, is having trouble restoring the nominal brightness of the trace, to the point of "undershooting" its target value, before progressively settling to the nominal brightness. Capacitive effect at play sounds plausible....Even before I recap the scope, I might just out of curiosity, have a peek at the manual/principle of operation, and schematics to see if I can figure something out...

author: tautech
author_rank: Super Contributor
timestamp: June 06, 2018, 09:15:44 pm
content: WRT the whine, I suspect and in part you confirm that component values around the SMPS controller have drifted but heat after a short period of operation lets it drift back into happy regions where the noise abates.But which components ? Could it be the IC ? Or even unrelated directly to SMPS timing as components in the switched current path will impact on the total circuit and therefore peak switched current. Check the 0.2R current sense resistor. You can see there's quite a few components that could potentially affect the IC's operation, from the VCC supply, current sense and timing. It all needs be carefully checked, particularly component values.Let's say 5% parts are spec'ed but they measure nearly 5% from value. I think that would have me replace them and check new parts like you did with the zener.When you start fiddling with switched magnetics you see some very interesting effects as the primary current gets high enough to cause primary saturation and this is what I suspect is happening. Just reducing the FET ON time a few ns can drop you below the start of core saturation and extinguish all whine.I think in your position before you adjust anything in the scope to attempt to fix the whine, build the same circuit deadbug or breadboard and experiment with some timing adjustments to get a clear indication of just what values need tweaking. All you're after is ON time adjustment 'indication' and you don't even need to switch any 'real' power.What is the SMPS IC ? Can you find a datasheet for it ? Is it still available ?Fun times ahead and you can learn heaps if you want to want to properly investigate this one.Just tread carefully. Little steps.

author: Vince
author_rank: Super Contributor
timestamp: June 06, 2018, 09:47:22 pm
content: Thanks for all the good info, a good starting point !The PWM chip is a classic TL494 from texas instruments. My 2232 had a TL594... not sure how they differ... internal block diagram is strictly the same. Whatever the difference, is gonna be very minor I think...They are still readily available, as is the datasheet on Google.Well, haven't checked availability of the 494 to be honest, but the 594 I had no trouble buying when I fixed my 2232 a year ago.

author: floobydust
author_rank: Super Contributor
timestamp: June 06, 2018, 10:00:48 pm
content: Old thread about Tektronix PSU whine:https://www.eevblog.com/forum/testgear/tektronix-2235-prblems/

author: tautech
author_rank: Super Contributor
timestamp: June 07, 2018, 01:39:50 am
content: Quote from: floobydust on June 06, 2018, 10:00:48 pmYes some pertinent info there but nothing that conclusively gives answers to this whine issue.Probably the best hint is here:Quote from: oldway on April 07, 2014, 02:38:02 amHowever to surmise that T906 could be the root of many problems without either insulation checks or dissection is just guessing.That Vince's one quietens down after a period of operation points strongly to temp related component 'real value' issues in the SMPS controller circuitry IMHO and not a faulty T906.

author: Vince
author_rank: Super Contributor
timestamp: June 08, 2018, 06:46:22 pm
content: Thanks for the help guys.Will read that 2235 thread when I get some time.As a starting point I think I will follow Tautech's idea, for the reasons he gives. Second reason is that my experience with my 2232 suggests that the tranny is not at fault : that scope was noisy before I worked on the SMPS (with all original parts in there) and it was still noisy after I rebuilt the regulator. The old tranny was cooked (FET went short circuit, the coil/winding in the tranny burnt open), and the ferrite core had a big crack in it, and the two halves of the core were misaligned.So, I assumed the horrible condition of the tranny was responsible for the whine.... but, not at all : the replacement tranny was in perfect shape, and even had the drop of white gunk / "silactic" in the center of the core (the old one did NOT even have that), that some trannies have, to keep them from vibrating/making noise.Yet.... even that new tranny was making noise ! Still is.I think what I would do as a starting point, would be to get a real cheap and dirty USB scope, so I can record a few signals for a few minutes after power up from cold. One of these signals would be the audio coming from the tranny, so I can then correlated the other (electrical) signals to the sounds they gets produced. I could then search for correlations. I could look at the oscillator of the PWM chip, at the voltage pulses from the FET, also the current in the FET/tranny.I can't do that with my digital scope (TDS 544A) as it has only 50K points of memory, when I reckon I would need at least 100M points.A USB scope isn't good for anything but... but this particular task : don't care about accuray, performance, bandwidth, or XYZ feature... just need up to 1MHz B/W or there abouts, plenty enough, and stream the data live to the PC, where ample amounts of RAM will make it easy tro record many minutes of time correlated signals, which I can then "play back" / study...Getting a current probe is gonna be the most expensive part by far... but then I always wanted one, so this mini-project is a great excuse/opportunity to finally get on, isn't it...The 2235 looks interesting.. from what I can see of it (front panel in pictures and videos here and there), it's basically a 2215 with a higher bandwidth, 100MHz vs 60.Anyway, the whine is a project for later, possibly much later, no idea, will see... have other projects...The immediate concern is to recap the scope and try to address this weird brightness issue in the delayed time base...Let's have a close look at the various boards in the scope, and list all the caps I will need to order....

author: Vince
author_rank: Super Contributor
timestamp: June 10, 2018, 10:20:11 pm
content: Spent my Saturday on the thing.... some good, some bad. Overall it seems like a very sick puppy, not sure I will ever be able to get it really spot on... but well for now I keep going. I think Floobydust must be right... the 2215 is a troublesome beast that was rushed to market... ahem...If really it appears hopeless, I would at least keep it as a test bed to investigate the SMPS whine issue. Also, regardless of the outcome, I enjoy the hands on experience it provides me with repairing stuff. I always learn a little bit here and there. Also gives me a deeper knowledge of the 2200 series scopes, which can only be a good thing as I intend on getting more of these, and if anything it will help me get better at maintaining my current 2232 which is my main scope.So, overall I am still quite happy that I bought this little 2215 scope.OK, so what I did today :- Went to examine the scope closer, to try and track down every electrolytic cap I could find, simply by visual inspection.Then tried to correlate that with the parts list. Doing so was interesting : I removed the sweep bard from the scope, so I could get a closer look at what I thought were 4 electrolytic caps... which turned out to be in fact a set of 4 matched caps, Tektronix branded, precision timing caps... make more sense indeed, but boy do they look like old electrolytic caps... from a distance.BUT wait.... there WAS indeed some electrolytic caps on this board, 2 of them, according to the parts list anyway ! For the life of me I could spot them at first glance. So looked at the component designator in the part list, searched for that on the silk screen underneath the board... OK found them ! Gee no wonder I had a hard time spotting them : they do NOT look like electrolytic caps ... see picture. They are tiny, axial things, silver looking. They bear the same dimensions as a 1/4 W resistor, and look like a precision film cap. Learned something new then. Granted, these electrolytic are indeed "precision" (by electrolytic standards ie...) caps : +/- 10% , a far cry from the usual -10/+50% of the usual electrolytic. Heck, there is even on in the scope that +75% !!!So in short : what I thought were electrolytic caps.. where precision film caps. And what I thought were precision film caps... turned about to be electrolytic caps ! Lessons learned.That was for the (main) sweep board. So in the end I have nothing to replace on this board. As for A11, the front panel board : one small electrolytic, not going to bother with that one I think. Don't think it can affect the scope that much (?), and is way to hard to get too : would need to remove the board, which I am MORE than reluctant doing, because when I tried to that on my 2232 last year, just about each and every of the small "position" knobs, the kind that just snaps onto their shaft... broke ! Plastic is way too brittle. They are hard to find and cost a fortune... still have not replaced them to date, a year later almost !So I hardly fancy adding another 4 or 5 of these buttons to my shopping list, if I can avoid it ! Luckily, removing the sweep board didn't involve any of these snap-on knobs, so I wasn't at risk there.Then let's look at the B/delayed time base board, A13. Just like the front panel board, there is only one small electrolytic cap on there, that's C659. However according to the schematics this one is not your regular dumb power supply decoupling cap. Nope, that one is part of the signal path for something of great interest to me : the 'B' delay vernier . So I will replace that one. Gonna be fun though, as the Alternate/B Sweep board , which is the one mounted vertically right next to the SMPS metal work... is not socketed ! Why, ohhh... why. It's a single row of no less than 27 pins, soldered directly to the main board : "lucky me"....I think I can manage to desolder it cleanly, given some time... but chances are hight that I will have to do most of my trouble shooting to come, on that very board... so I will solder a socket on the main board, so I can pull that daughter board at will. Gonna add a 32th of an inch of extra pin inductance... probably not the end of the world on a 60MHz scope... I shall see for myself anyway.Then the last board to look at is... the main board, A10. Other than obvious SMPS rear of the board, I could not see a single electrolytic.... the "bad"/usual type I mean. But I did see a (very) few of these small precision axial electrolytic caps, same kind that I found on the main sweep board, A12. Again, I am not touching these.So... to summarize the recap job ahead :- A small one on the 'B' sweep board.- A handful in the SMPS section, but not that many actually. 10 it appears, a nice round number.- Time base knob issue....I didn't mention it so far I think, but the delayed sweep knob was a bit of a pain : I had to pull it so much to get it to engage, that invariably it would pop the little red x10 Mag button with it !Also, it had an incredible amount of play/slack in it. sometimes the spring action would vanish, letting the know slide freely on its shaft... I feared that the big timing switch on the A12 board would be damaged, the end of the world... in the end it turned out the switch is perfectly fine, and all that was needed was to tighten that bloody knob, it was just a little loose. Problem : to tighten it, you need to removed the red knob, then we can access a nut in inside the knob, concentric to the shaft. Being an old USA bit of kit, the nut is an imperial size : 1/4" . I do have a set of Allen/hex male keys in Imperial sizes, but that's about it. No female hex socket to go get that screw well recessed into the knob...... or maybe I do ?! Hmmm... 1/4" happens to be the size of all screw driver bits ! With every power drill or 1/4" ratchet wrench tool set, usually they also give you a little adapter that let's you fit the bit to the drill or wrench. Have a few of them. One was slim enough (outside diameter I mean) to be able to get inside the knob... but hell, the adapter was not DEEP enough to reach the nut ! It could barely touch it but not grab it well enough to turn it. Never mind... I reworked the adapter to make it deeper, and hey presto, now I can tighten that nut/knob at last !And sure enough... it now works like a charm, no play, no nothing, it just works, like I bought one !Problem : I will actually HAVE to buy one ! When I did the test, the sweep board was outside the scope... when I refitted to the scope and therefore had to tighten again that nut... yeah, the thread of the insert that grabs the (splined) shaft... sheared off ! The insert is actually not part of the knob, it could be replaced... but go find someone selling this tiny piece of metal ! So, I will have to go find en entire knob assembly just so I can have a new insert... which obviously is just as likely to break. Why did Tek use crap metal for this part ? Beyond me.But the good remains that I now know that the this knob can be made to work just like new, no worries, no matter how old that scope is (36 years) !- Main board reworkOnce I had removed the sweep board, I now had a clear view on the main board. Did a visual inspection. Found a chip with what looked to me like 3 corroded pins ! Grrr.... See pictures. I cleaned that with IPA and an ESD safe "toothbrush". Then a chip next to this one... looked like it had a cracked solder joint on one of its pins ! Grrr again... so I bit the bullet, turned the scope upside down and proceeded to reflow (while also adding a bit of fresh solder) each and every pic of each and every chip I could spot ! Shy of 20 ICs IIRC. Can't harm...The eagle eyed will notice that next to the chip with corroded pins, there is a Zener diode... which appears to suffer the exact same disease as it's Zener friends on the pre-regulator board : their leads are completely covered with a black oxide of some kind. So there is definitely a pattern here....- CleaningSeeing as I had the sweep board out, I flooded the rotary switches (2 vertical amplifiers + timing switch) with contact cleaner and exercised the switches a few dozen times. Did the same to all the switches on the front panel. Many are not easy to reach, but with the hepl of the straw, and turing the scope in every imaginable position... one can managed to do all of them bar one IIRC. The small pots for the position knobs and trigger knobs, however, are sealed, so no hope there. They seemed to be working fine though, so it's not a big deal...Then I proceeded to clean the front panel. Doesn't show no my pictures so far, but up close, in the flesh... the whole things was pretty off-putting. 36 years of use, well it does show....Again I didn't want to risk breaking all these little snap-on knobs, so I cleaned all of the knobs and switches in situ. Spending a few minutes on each and every knob, until I was satisfied with it level of cleanliness... so to speak. The CRT bezel and color filter were easy to removed (just a couple Torx screws from the front of the instrument), so I removed them, made cleaning theses parts, and the area, easier.A gallon of cleaning product, and a tired toothbrush later... the front panel now looks, up close, as good as new, I dare to say ! It can withstand macro shots no worries. I might still come back to it for a couple minor improvements :- The clear/transparent plastic skirts for the sweep knob and attenuator knobs. Up close, they aren't 100% transparent. Really nitpicking here, I admit, but I think with a bit of polishing they might come up really great, really glass-like clear. So worth a shot.- The aluminium vernier looks great, except for the tip of it : the small part that you use to actually grab it with your fingers. It has seen better days I think... I could remove it (just a screw) so I can work it properly, on a polishing wheel or something.Apart from that, front of the scope looks really pleasing now, quite happyJust need a bloody replacement time base knob to finish it off !Then I also spent quite some time looking at the schematics to try to figure out the circuitry responsible for highlighting the portion of the 'A' trace, that the the 'B' sweep displays/zooms into, with regard to the dark spot that trails behind the intensified portion. But it's a whole new can of worms as it happens, so will leave that for another post... this one is long enough, I admit...So for now :- Order all the caps so I can recap the thing- Order some kind of socket/in-line connector so I can socket the alternate sweep board to assist in trouble-shooting- try to find a replacement time base know (Sphere, Qservice or whoever on ebay...) and while I am at it try to find snap-on knobs for my 2232.A few pics and straight to bed... again late and tired. Sorry for the inevitable typos, will fix them tomorrow when I get back home. In the meantime, be forgiving and try to make sense of stuff where ever it looks a little weird.

author: Vince
author_rank: Super Contributor
timestamp: June 11, 2018, 09:56:25 pm
content: OK, not much time during the week to work on it... but every little helps :- Desoldered all the caps that will need to be rfeplaced, and double checked on the parts list that the few that were replaced... half of them actually (5 out of 10 ! ) where the appropriate value, capacitance and voltage rating. Somehow, they were all spot on.The guy who replaced these 5 caps, for once, didn't buy the cheapest/crappiest he found from his local store : he put Nichicon everywhere but one which was Nippon-Chemicon, which is good also IIRC. However.... he used 85°C caps for all of them... when even the prehistoric Mallory branded original caps... were all 105°C rated ! I means, the old/original FET (which is still in place) is very inefficient/heats up a lot, and the scope does not have a fan to top it all !Also interesting : even though the scope does not have the TRIAC based regulator on the main board, but rather the PWM daughter board... the big filter cap of the regulator output did not move from the main board of the daughter board... no, they put one on both ! So a 470uF cap on the PWM regulator board, and the 470uF cap that came from the old TRIAC design. So that's almost 1000uF in all. My only assumption here is that there the two wires aht connect the output of the PWM board to the input of the inverter on the main board, are quite long, 6 inches or so, 12 total... maybe that was too much parasitic inductance, and they wanted to still maintain some "local" decoupling right at the input of the inverter ? Probably...I also see that one of the replaced caps... was probably replaced under warranty ! It's one of the many (5 of them) 840uF 12V Mallory caps.I am petty sure of this because the replacement cap bears a part number on it and, most importantly, has the exact odd 840uF / 12V ratings ! Now if the average joe goes on-line to fine such a cap, I wish him good luck ! 820uF 10 or 16V yeah sure, that's standard, but 840uF ? Nope. 12V ? Neither...So that goes to show that these Mallory caps didn't last all that long to start with.Now... with only 12V rating, what the hell...I will up the voltage rating quite a bit I think. Dimension wise, the only constraint in this SMSP is the diameter, because 3 of these 840uF caps are touching each other, so I can't afford the replacements to be even one single millimeter bigger than this.Capacitance wise, the parts list give the tolerance for these 840uF caps as being... fasten your seat belt.... +20% ? + 50% ? ...... nope... they state + 100% !Just had a look on-line to see what's available, Think I will put 1000uF as it's a nice round value with a lot more choice and low prices. Luckily, it appears that diameter wise, 12,5mm is a very popular package. Just under the 13mm mark I had to obey, perfect ! And even in thise diameter, they can withstand 25 or 35V, much better than the original 12V. Price wise, I searched for Nichicon and Panasonic, 105°C, and even then it's only 50 cents or so a piece !So no worries.Apart from that... I am getting really tired of printed schematics from these Tek manuals... They are usually 3 page foldouts, so even much larger thanA3. Whenever I want/need to print a schematic, I need to select a small portion of it so that it's not too small/readable on my A4 paper/printer. But even this is a pain, because the PDF reader (at least the one that comes in Linux/Gnome) doesn't allow to select a rectangular area on page, and print that so it fits an A4 page. So I have to full screen the PDF reader window, and and zoom and pan the foldout to select some part of it, then do a screen capture, then past it into an image editing software, then rework the image a bit from there, and print it... but obviously the result is not always readable because the screen capture is 90dpi or so, when a print would need 300dpi or so to look "clean".So for example today I would have liked to print a board view of the main board, to highlight the caps that I removed from the board, to assist in putting them back later. But I couldn't be bothered because of all the process I just described... so instead I just drew sketch by hand ! Ugly, but super quick and does the job...So, I think I am now so tired of doing this over and over again, every time I get a new old piece of gear in the lab... that I might bit the bullet and get myself an A3 size printer. Think I saw one not too long ago, for less than 100 bucks new. Ink jet of course, so the cost per page is high, but I don't care because I am not gonna prints millions of foldout a year, and I only need huge black cartridge, not expensive color cartridges.Then I ought to try and see if there is a PDF reader that does allow to easily make a rectangular selection on a scanned page like these old manual, and print just that, at full res/high dpi. Maybe Adobe's reader can do that ? Would have to run it in a virtual machine though... but still, I would do it.But ultimately even A3 printers don't cut it for our typical 3 page foldouts... so i am now even considering getting a plotter ! With a roll of paper, one could print foldouts of any length, no worries !I mean yeah, these things are expensive, but maybe I can find a small one (with a width equal to the longest side of an A3 sheet), and of course a used one would be just fine....Plus, it's doesn't have to be state of the art, it's just to print black and white schematics. Doesn't have to be super fast, nor do color, nor have silly high resolution,nor be top quality... yeah I think I will start investigating this path seriously soon ! I am really soooo tired of the current situation !Midnight, late again... goodbye...

author: tautech
author_rank: Super Contributor
timestamp: June 11, 2018, 10:12:13 pm
content: What about taking a pic of the PCB and importing it into Paint or a similar basic editor and highlighting the ones you need there ?WRT the big schematics, use the printer settings to print them on say 4x A4 pages not just 'fit to page' as some printer do. Use Print Preview to see what other available printer settings can offer you.

author: Vince
author_rank: Super Contributor
timestamp: June 11, 2018, 10:40:46 pm
content: Quote from: tautech on June 11, 2018, 10:12:13 pmYeah, but the computer is in the living room, and lab/scope is upstairs... so every time I need to take notes, I need to have it in printed/paper form so I can then get upstairs and annotate it. But yes I do use pictures as well, to document the disassembly process, help me when I need to put it back together again. In this case I took that close up shot of the SMPS so I could have an overview of all the caps I was interested in, and remember where were fitted the non-original caps for example.Printing the picture is not really an option I fancy, because fuil size pics are painfully slow to compute/print, and since my 21 year old HP LaserJet 6P printer is only black and white, pic is grey scale and this gives poor contrast and makes pen writing hard to see no matter what colour I use. A black and white schematic however, is ideal. Excellent contrast, easy on the eye, and can use any pen color I like, they are all easy to see.I am thinking of upgrading this old B&W laser printer to an A3 colour laser, but good ones still cost a bit of money (by my standards anyway). Plus, I just love this old Laserjet 6P. Cost me a month worth of salary when I bought it new in 1997, but look, 21 years later, still works/prints perfectly, and cost per page is ridiculously low compared to an inkjet printer : the original toner/cartridge lasted 4000 pages.. exactly what its advertised life expectancy was ! Replaced the cartridge 10 years ago... still running ! Just printed the status page to give it a check : counter reports 5121 printed pages, so about 1200 pages using the new/second toner, still 2800 pages to go !I mean... it's worth nothing on the used market, absolutely nothing. So why sell it ? I like it very much, works like it were brand new, cost per page is next to nil... it's the ultimate weapon to print regular A4 pages from manuals and datasheet etc !.... except it's not the best choice for printing foldouts... or colour pictures, or colour charts, or web pages...QuoteYeah that would be great ! But historically, printer drivers in Linux, when you are lucky enough to have one available for your printer... well typically they aren't quite as feature-full as their Windows OEM counterpart. In the case at hand, the driver lets me put several pages on a single sheet of paper, but not spread a single page/foldout onto multiple sheets.. too bad...Short term I think the best bang for buck would be as I said to get a cheap A3 B&W inkjet printer and try to find a PDF reader that can let you select/print a portion of a page rather than the whole page. That seems like an attainable goal. The small plotter would be in my dreams, but sure would be ideal....

author: tautech
author_rank: Super Contributor
timestamp: June 11, 2018, 10:51:47 pm
content: I have a HP 6MP too and it's been a great printer but we also have a 1200dpi color OKI too but we still use them both. With Windows the printer drivers or pdf viewing SW has allowed several printing options that can help get you the types of prints you need.Yeah I get not having a PC near your bench is a curse and something I quickly dealt to years ago when I did lots of repairs.A PC close and handy to the bench is just as valuable as your test equipment IMHO.

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: June 12, 2018, 01:19:18 am
content: If you want schematics printed download them to USB and rake them to your local office print store.There are more than a few around us and I live on the edge of civilisation! large scale sized prints, A2, are really not that expensive.Sent from my iPhone using Tapatalk

author: Vince
author_rank: Super Contributor
timestamp: June 12, 2018, 06:37:28 pm
content: Quote from: tautech on June 11, 2018, 10:51:47 pmI agree.... it's on the cards ! Problem is that my "vintage" computer (mid '90's IBM "Aptiva") already takes that spot in the lab, with it's bulky tower case and CRT monitor...so no space left for a more modern/useful PC.But in 6 months or so I will hopefully move into my own house, so will have more space. Will move the old IBM somewhere else, so I can put a more modern machine to serve all the lab duties. Think I will take a flat/ LCD monitor, and very compact computer case in the style of the old "mac mini" (but won't be a Mac), so that it takes as little space as possible. After all I don't need much processing power nor I/Os : a few USB ports, Ethernet for internet, a "true" RS232 port, VGA output and that's about it...Hopefully I can find such a computer for cheap. I mean my current desktop/main PC is 10 year old (and 3 months...), yet still plenty fast enough for an,ything I have wanted/needed to do with it. A core2 duo 2.66GH, P8GB of RAM. So I would try to find similar specs but in much more compact form factor. Hell, a 20 bucks Raspberry Pi might even be plenty powerful enough ! LOL Don't know, but probably...

author: Vince
author_rank: Super Contributor
timestamp: June 12, 2018, 07:07:17 pm
content: Quote from: wasyoungonce on June 12, 2018, 01:19:18 amHi WasYoungOnce,I don't have such store in my little 4000 people village (with as many cows, hens, horses, sheeps etc....). I would have to go down town, about 15kms away, 30kms round trip. About 2 liters of fuel, at about 2 US dollars (equivalent of) per liter, 4 bucks + the cost of a parking space, say one buck if I make it quick to the store. so 5 bucks just to get there, not mention the time spent, about an hour and a half total. Plus the fact I could go there only on Saturdays because no time during the week, store would be closed by the time I get there after work.To make it worth the trip I would have to print the full set of schematics, several times (usually I need more than just one print of a given schematic), which would add up to a sensible amount.... and 90% of that would be wasted because I would obviously not need several prints of each and every page... but of course you only know this once the repair is finished...So.... it's both highly impractical as well as economically disastrous, from my point of view anyway... YMMVMy best alternative to date, is to print them at work. Put the manual on a USB stick as you said, and printed at work, on the big A3 "do it all" Xerox copy machine. Gave it a try today. I printed a selection of schematic sheets, to cover all use cases (exploded view, board layout with component designators, block diagrams, schematics...). They use Acrobat Reader ' X ' (no idea how old it is.. but copyright states states it's up 2011), and it does have the lovely feature I was dreaming about : you can just select a portion of foldout, and print just that, and make it fit to an A3 page. Most foldouts are 3 page wide, however schematics always use only 2 of the 3 pages, the last one is usually used to show whatever else : a table with component coordinates, waveforms, some text, whatever.So the schematics are actually A3 sized.... so printed on A3 sheets, they came out just fine.... no need for a plotter in the end, great !The only 3 page foldout where the "object" actually spans the full width of the foldout, is the block diagram that represents the entire scope. But the requirements for a block diagram, is not as demanding as schematic. (no small prints to read, no need to annotate it all over the shop etc), so when shrunk a little to fit it to A3, it's still perfectly usable, no eye strain.So looks like this is it then. I need to open the service manual in a Windows virtual machine so I can use Acrobat reader and have this feature that lets me select an arbitrary area of a page, and print it in full res. Then just get a cheap A3 B&W inkjet printer and call it doneHardest part for me would probably be to get that old parallel port LaserJet to work from VirtualBox.... configuring VM to get direct access to H/W resources is not my strongest point !But well, it's worth the trouble since It would solve my problem and make me happy !!I am sure there is no shortage of people on XYZ forums to help out with configuring the VM...OK once I have moved into the house late this years : get a new PC for all lab duties, and an A3 printer, and that will breath new life into my "repairing old stuff" activities !OK so now let's order all those replacement caps... should be able to get them in time to fit them this week-end, hopefully.

author: Vince
author_rank: Super Contributor
timestamp: June 16, 2018, 07:06:53 pm
content: Alright... knobs....To sum it up : the knob "situation" on the 22XX scopes is.... appalling. My worst nightmare... it's not even a question of money and economical viability.. it's simply a matter of plain availability !I need 4 of these little snap-on knobs to fix my 2232. Been a year. Two major sources are "Sphere in america, and "Qservice" in the US but who luckily also have operations in Europe (Greece) which means affordable shipping for me, as well as absence of customs. Still, after a year, neither have these knobs. Sphere has "close enough" models, but not quite what I need, and they cost 15 dollars EACH, and they only have 5 of them. Add shipping and customs, and that's 100 bucks for 4 little knobs that may just as well break like the old ones, when I go to fit them.As for the sweep knob for the 2215, again none at Qservice (listed but no stock). Sphere has one but 15 bucks... says it comes complete, with the center core (I guess that refers to the little part I broke/need ... but no guarantee ). Add all the charges and it comes to me.. it will be worth as much as what I paid for the scope itself !So I am still trying to find a place that would sell/detail this kind of part... but no luck so far.Spent some time on-line about it... think I know the correct English vocable/terminology now... helps a lot in finding what I need.The most common knobs with screws on side, are called "set screw" knobs.The model I need, with a hidden central nut, are called "collet" type knobs. The part I broke is precisely called "collet", which gave its name to this type of knob.Then there are two types of collets : ones which are tightened using a screw, and those which use a nut. The latter is obviously the only type which allows a shaft to go through it, so that's what I need. Looks like they are called "through-hole" collets.So far I have been unable to find a hardware store that would sell individual collets. Everytime I try search for "buy through-hole collet", I am directed to shops that sell tools for metal metal machining : lathe etc ), so not quite what I am after.My only option I see for now, is to buy a cheap complete collet knob, so I can destroy it and salvage the collet from it..; hoping its collet (dimensions) would fit the Tek sweep knobs (tooks all necessary measurements from it).But... yeah, again it's not that simple : after a fair bit of searching, it appears that knobs using through-hole collets... are only large knobs for large 1/4" shafts, and the small knobs for 1/8" shaft like the Tek shaft, use screws not nuts, so no use for me. I understand why this is.. the rationale being that when you stack two knobs, only the biggest knob needs to be through hole, and the small knob doesn't need to be through-hole, because it's two small to stack another knob on top of it anyway. ....... soooo, even buying a new knob is not that easy ! Finding one that is through-hole AND at te same time made for small 1/8" shafts, is a challenge ! After lots of searching, Ebay finally found some for me... the guy sells 3 sizes of theses knobs, so many the collet on one of them can fit the Tek knob, or be made to fit with minor rework. but still... not as cheap an option as I would like : he only sells them in packs of 2, 4 bucks. Would need to by all 3 models he sells, to get a chance to have one that maybe fits the Tek knob... that's 12 bucks. And the guy is in the US, so again expensive shipping + customs !And still, no guarantee that one of these knobs would fit !So... since the complete, proper model knob from Sphere is barely more expensive, at 15 bucks...and would be guaranteed to be the proper model/fit, hence zero risk.... this might still be the "safest" option. So I am thinking of that. Of course I would need to contact Sphere to be 100.00% sure that the knob (unlike what the pics show), DOES come with the collet and nut, as the description suggests.In the meantime I must still try hard to find a place that might sell/rtail collect, so I could get one locally and dirt cheap. However I getting pessimistic about it : seems to me that no two knobs have similar collets : the shape and dimensions of each and every knobs, calls for customs dimensions, I feel. So I think that knob manufacturers must make (or get made) these collets to their own specifications...Still, might post on the forum about this, in case someone knows better and might know where to get this stuff from ! Worth a shot...CONCLUSIONI think I will have to rethink my "strategy" about these 22XX scopes... this knob problem is a real show stopper. What the point of spending time and money fixing one of these scopes.. if at the end you can't complete the repair because of lack of bloody knobs !Now I am no purist... fitting a non- Tek part is no trouble to me, as long as it makes sense (like recapping the scope). But as far as knobs go... it's not a matter of being a purist, it's just a matter of aesthetics ! Sorry but there is no way, no way that I can stand the looks of a non original knobs on an instruments, any instrument.. it just ruins the entire "experience", stand out so much, drives me nuts... Some people just don't care, as long as it's functional... I get that. I wish I were like this ! But I am not. Half of the reason I like old gear, is the look and feel of the front panel/user interface. Other half is performance and feature set and engineering quality of course.So, given that these brittle little knobs are so hard to find, next to impossible, and are so expensive that thety cost as much as the scope... I am now to the point where I think I might have to collect cheap and low end 22XX scopes, ugly, broke,, fallen form the 50th floor, imploded CRT... purely to have spare knobs and switches to help me maintain and fix my main 22XX scope, the ones with good specs and in good nick, which I would actually use.So I would consider all 22XX scope I can find locally, for say 100 Euros max.So short term, my revised plan now would be :- If I fail to find a place that retails collets, then go buy the one from Sphere, once I am sure it does come with the collet.- Then I could use have a go at troubleshooting this weird dark spot problem trailing behind the intensified portion of the trace.- Then use the scope as a test best to investigate the SMSP whine issue... and then store the scope and use it as a donor. I would harvest those snap-on knobs to fix my 2232/main scope. The brand new sweep knobs I might sell to try to recoup some of the cost. I won't sell the scope. It's more useful as a donor for my 2232, and as test bed for the whine issue, and as a sick "patient" to help me learn trouble shooting, improve/build my repair skills. This dark spot issue is really weird. the more weird the issue, the more you have to search for the answer, and the more... you learn.So, this little 2215 scope is still very useful in many ways, given the low price I got it for, but yeah, although I will keep it, unless I find cheap push-on knobs, I don't think it will ever complete and used on the bench..It drives me nuts not be able to use a mint and working scope just because you can't find bloody knobs to complete the front panel, it really drives me mad... but that's what the situation is ! So I must live it and admit that this 2215 scope is more useful and valuable as a parts unit ....Working with old gear is sometimes very frustrating indeed... the lack of parts is a pain when it strikes !

author: Vince
author_rank: Super Contributor
timestamp: June 17, 2018, 08:19:55 pm
content: Grr... I was hoping to get the new caps in time for this week-end, but no luck !I ordered fromhttps://www.tme.eu/en/as often. First class service usually.. but this time some thing is wrong it appears...- My first order, I canceled at teh last second because I realized I forgot to order one of the caps. So I did NOT enter my credit card number, and I cancelled the process/closed the window and came back to the shopping cart... but somehow they validated this pseudo order, and I received an invoice via e-mail, and the order does show up in my profile/customer space on the web site ?!- As soon as I had canceled the first order, I filled my shopping cart all over again, from scratch (it did NOT remember the previous content... crap), then I paid this one normally, and got the invoice in my mail box, as you do. But.... that was 5 days ago, and still no news from them. The order does not appear to be processed at all, they have taken no steps at all... like they are ignoring me ?! Normally, in 5 days I would already have received my parts ! So something is wrong with them... I sent them an e-mail to inquire about it... hope they will fix the situation promptly.I want my caps !That being said... I now realize that I was so focused on ordering the ELECTROLYTIC caps.... that I completely forgot to order the 3 tiny green dipped ceramic caps that go with the PWM chip, oh no !!!! 10 Euros worth of shipping cost to endure again... for 50 cents worth of ceramic caps ?! Tragedy...

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 17, 2018, 08:30:59 pm
content: Should I sell any of these (Tek 2230) before I pack for moving? After that they'll be out of reach for a while...

author: Vince
author_rank: Super Contributor
timestamp: June 17, 2018, 08:46:49 pm
content: Hi Paul,I didn't recall that you had a 2230 ! What happened to it ?!You didn't manage to fix it (I can't believe that for a second) and the knobs is all that remains from that scope ? All the rest is gone ?Well, that's quite a lot money laid on your bench here ! Wish I had enough money to pay for that... but please don't throw them away... I do intend to hang onto my 2232 as my main scope, for a while, so I would probably buy you the lot in a few months, depending on price...However unless I am blind (picture is not very high-res), it looks like you did not manage to salvage any of the so precious and rare, britle snap-on knobs, the 4 used for the position controls, the 4 that I broke on my scope....Still, would be nice to have the rest of the knobs, for sure... can't hurt.I think I will buy another 2232 or tow, in the future, if I can find some moderately priced... yeah not an easy task in our neck of the woods I admit !So your wooden house is finished at last... when do you plan on moving exactly ?? My house is on the way too... hoping to move by the end of the year. Late October with some luck...

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 17, 2018, 09:56:31 pm
content: Hello Vincent,I picked that 2230 up from industrial scrap back in the time I didn't have "that many scopes", I did think of trying to fix it but it was missing the cover and the remains had been crushed a little by a fork-lift, so I actually gave the idea up pretty fast and kept the parts.I seem to have 5 snap-on knob caps, 2 of which have partially lost the "snap".The house isn't finished, that's why all this electronics junk will by out of reach for some time, I'm moving in august, into an incomplete place and will have to store the treasure in the meantime.

author: Vince
author_rank: Super Contributor
timestamp: June 18, 2018, 06:52:34 pm
content: Hi Paul,Quote from: shakalnokturn on June 17, 2018, 09:56:31 pmOkaaaaay... that poor scope never even stood a chance then... crapQuoteAh, some broke. I feel less stupid for breaking mine then...I am so desperate that I think I might contemplate trying to glue the broken bits inside the knobs.... nothing to lose.I am glad I have these 2215 as a donor for my 2232. If just for that, it was worth buying it.Of course we could 3D print these... but the feel, surface finish and colour would never be a good enough match... even if subcontracting the job to a specialized company that use million dollars high-tech printers. Maybe one day... maybe in 100 years.... until then, harvesting knobs from a donor scope is about the only solution.QuoteOK get it.... sorry about the situation. I hope it won't be 2 years before you can bring all your stuff back into the house !Well come to think of it.. I am pretty much in the same situation ! The lab is supposed to go upstairs, as I don't have a spare room on the ground floor. Only problem is that there won't be an "upstairs" to talk about, until I have turned the attic into a place compatible with the presence of human beings... and this is expected to take 2 or 3 years. Until then... the lab will actually occupy 60% of the living room... back to the old days then, when I was living in small appartments...

author: Vince
author_rank: Super Contributor
timestamp: July 03, 2018, 09:27:35 pm
content: Alllllll - riiiiiiight..... worked a bit on the thing last night...RecappingI received a bunch of caps from TME. They have really a great choice of electrolytic caps. Even when narrowing down the search to only Nichicon and 105°C rated caps, I still had the choice between several series of caps ! So what to choose ?! A normal person would just pick the cheapest, or roll a dice.. but of course an electronic guy has to make rational/informed decisions, so I had no choice but to download the data sheet for all these series I was offered. Mostly VX, VY, PM and PW series, then compare them and try to figure out what would be best.I am hardly an expert so was not straightforward... but in the end I decided to go for the PW series where possible, else pick PM, but leave the VX and VY alone. VX and VY look like your cheap and short life high losses filter caps for linear supplies. The 'P' "series of series" so to speak, looks more like it's designed as low ESR for SMPS use, and longer life/endurance. If anything, PM/PW data sheets give you the actual ESR, down to the milli-ohm, for each and every voltage/capacitance combination possible... whereas the VX/VY series don't. They just give you a rough "losses" factor for the entire range of caps, no detail.Then, when you open a datasheet (all 4 attached below) , they show you a little diagram that links the series to other series... so there you learn about even more series that you didn't even know existed ! More confusion ! Who knew there could be so many different models/types of electrolytic caps ?!So to decide between PM or PW, the impression I got was that PW was the slightly improved version of PM, about to supersede it. Slightly lower ESR, longer life, smaller case... though if you look at the tables/hard facts, at least for the caps I was concerned with, the PW was exactly the same package/dimension, not smaller, and the ESR was so marginally smaller that it was not a decisive factor. Like 29mohms vs 30, IIRC.Still, it was a bit better and meant to replace PM short term. Also, the PW was often much cheaper than the "old" PM.Then for some of the caps, I swa a 'PS' series, which cost 10 times more than the PW... IIRC the PS is so outrageously expensive mostly because of its astonishingly high life expectancy, from memory, something like 20,000 hours when the PS and PW are in the 5000/8000 range, and the VX/VY series in the 1,000 range...So, basically, not all electrolytic caps are the same...you get what you pay for and make an informed decision.So , I ordered mostly PW, and PM only when the PW was either not available, or its minimum order quantity was like 100 or 500...Sorry for the long paragraph but well... that's actually what one has to go through when ordering something as simple as caps... nothing is really simple, the more choice you are faced with, the more time you end up spending figuring things out...Reading the manufacturer datasheets closely is a good way to learn about the subject, when like me you don't know all that much !I would be interested to see a technical paper from Nichicon or other good brands, that explains the gory details of just what's involved in making a cap last longer than another, and what's involved in achieving a 105 or even 125°C rated cap, compared to a common 85°C cap.Some caps I ordered 20 of them because they were so small, literally 5 cents a piece, so 20 was the minimum order quantity. Well, I have dozens of caps in my drawers now, can't hurt.So I replaced all those caps. Went pretty smoothly. Some were a bit of a gamble because the track was on the component side, so you have no way to be sure that the solder flowed through the hole to reach the underside of the cap... all you can do is heat the lead/pad for a decent amount of time to make sure it's well heated, so the solder can flow well and hopefully get to the other side of the PCB.. and add more solder than usual, to make it fill the hole and have some left to make the hidden joint.I also replaced the 2 caps on the pre-reg board, the ones I had already replaced the other day for test purposes, with crappy caps from my local electronic shop.Only cap I did not replace, as discussed earlier, is the big 450V mains filter cap. However I did order a couple anyway... just in case I somehow decide to replace it. This I will have them handy. These aren't cheap t 5 Euros a pop, but... even I don't use them on this scope, I could still reuse them later on no problem, since pretty much all SMPS supplies have a 450V electrolytic cap to filter the mains... so these caps aren't wasted, no worries.That's for electrolytic caps. Sadly TME has an extremely limited selection of dipped ceramic caps, either that or I am blind and did not find them. So I have not yet replaced the 3 little axial green ceramic caps that revolve around the PWM chip. Will have to order these from some other place, yet to be determined...Anyway, it didn't bother me too much because the scope was working just fine even with one of these caps missing, and a doubt on the health on the other two. Plus, the pre-reg board is easy to access later anyway, not much involved, so the caps can be replaced any time.MOSFETSeeing as the SMPS (main board I mean) was fully recapped, I wanted to put all the shield and pre-reg board in place, so as to have it in it's nominal configuration before testing the supply rails. This meant I had to remember... how to put the FET assembly back together again ! Tried to improvise, no good. Luckily I had a coupe pictures taken during disassembly, that clearly showed how it's put together, phew. Never be afraid of taking loads of pics when you take stuff apart... it will be your savior 6 months later when comes time to put it all back together !You can never have too much pics... you can never know what picture will be the one that might save your bacon later down the line !So one thing leading to another.. the legs of the old FET, broke as I had to bend them to put the FET back into its plastic holder/box. Didn't think that soldering the pins would be very elegant nor anything to be proud of, so I took that opportunity to replace the FET with the modern replacement I had bought. I didn't find the usual IRF something model, so had to improvise and just use a parametric search and pick what might be suitable... I stumbled on some weirdly named part I had never heard about, it's aIPP60R280P7made by Infineon... I thought these guys only made memory chips ?! Apparently not... you live and learn.PDF (too large to be attached) :https://www.infineon.com/dgdl/Infineon-IPP60R280P7-DS-v02_00-EN.pdf?fileId=5546d4625b10283a015b1f973023047bThis part as one would guess, is at least no paper much better than the old IRF820, which was 2.5Amps and 3.0 ohms RDSon. The Infineon part can sustain at least 8 amps, and RDSon is literally an order of magnitude lower, at 0.28ohm. Sounds almost too good to be true, but well, they had the guts to put that in their datasheet so I guess there must at least some truth to it ! Hell, even if it's only half as good as they say, it would still be much better than the old IRF820 !Later I realized one pesky detail, ahem... there is one little "detail" that the old IRF820 DOES feature, that I didn't think of taking into account when I search for a replacement : the IRF has an INSULATED tab ! It's not connected to the drain. Oh noooo... need to search for another replacement then... and spend hours pulling datasheets, because the parametric search engine does not offer to search for tab insulation, bummer... would have been too easy eh ?!so, I evaluated the risk I was taking by using that my non-insulated replacement...For one, the FET is not fastened to a heat sink ! Far from that : it's covered by a pretty thick (1mm or so) ceramic "pad", itself covered by what must be (?) some kind of EMI shield, which takes the form of a piece of FR4/fiber glass... that's yet another layer of insulation. So at least it looked like the tab would not make the chassis live and kill me, a good start. Then I looked at the possibility of the tab coming accidentally in contact with whatever in the scope, a lose wire, anything...but everything in the area is tightly held, and also the FET is not out in the wild far from that : it's completely isolated in its little brown plastic holder/prison... it's covered all around, no way a lose wire, or even a lose screw, could get inside the holder and come to contact the live tab... ).So, I decided I would solder my replacement FET in place, and put the SMPS all back together again, all the shield and mounting hardware, all in back in one piece again.Honestly I don't understand how Tek though it was OK to leave the FET swithching the juice all day long, with no heatsink and zero airflow, not even still air.. literally sealed in this plastic holder ?!More incredible is that despite this, and the high RDSon of 3ohm, hence lots of losses/heat... this FET did not melt !Or maybe it did and was already replaced once... or twice, or thrice... or frice... LOL ! what should we say after thrice...Anyway, at leas the modern replacement with it's 10 times lower RDSon, can only help ! Maybe this one won't fry... we shall see.TestingFinally, the moment of truth : will it work, will it blow, will I get electrocuted, or or or or.... ?!Luckily none of the above, I am glad to report !Scope still alive. I checked all the rails one by one. First the reference rail, -8.6V, because all the other rails are tied to this one. It was well within spec so I did not even consider touching the trimmer to try to make it better. That rail has a very tight tolerance +/- 40mV, and I was down by 15mV. So I left it at that.All the other rails measure well within spec as well, as could be expected. As for ripple, it was getting late last night, so didn't feel like firing a scope to get the real picture, so instead, I went the cheap route : just checked with a DMM in VAC mode, to get a taste for it. It's got a very decent RMS bandwidth of 100kHz, and the SMPS switches well below that, at 40kHz for the pre-reg, and only 20kHz for the inverter. So the DMM would get a fair share of the spectrum, the reading would hold water, I thought. Obviously the manual states Peak to Peak values, not RMS, but well as a rough approximation, I thought well, let's say the RMS shall not be more than half the P-P value, say. Hardly scientific, but well, you get the idea.So did that... and the DMM showed.... ZERO millitvolt ! Not one. A rock solid, steady zero mV ?! Too good to be true. Couldn't possibly trust that, could I... so I tried another DMM (same specs), and it agreed ! Eh ?! Hmmmm....So in the end I did eventually fire up a scope, my 2232 as usual, to get a taste of what was really going on.I was not disappointed, my DMM did not lie to me ! Scope has much higher BW of course, so I do get some ripple, but so tiny ! Max sensitivity of the vertical amplifier is 2mV pr division, and well, I get about one division P-P ! 2mV P-P ! Geez ! The manual requires less than 10mV P-P on all the low voltage supplies (5V and symmetrical 8.6V), and I get 2mV only !30V rail allows for a bit more ripple of course, up to 50mV, and I measure a grand maximum of 25mV worse case, only 15mV when averaging the waveform to get rid of the random crap and get a more stable waveform. The 100V supply can do with up to 200mV ripple, and I measured a bit less than 100mV. So again well within spec !Rail Tolerance Measured P-P ripple Measured- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --8.6V +/- 40mV -8,585V < 10mV 2mV- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -+5V +/- 0.25V 5.03V < 10mV 2mV- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -+8.6V +/- 260mV 8.54V < 10mV 2mV- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -+30V +/- 1.5V 30.2V < 50mV 15 to 25mV- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -+100V +/- 5V 100.3V < 200mV < 100mV- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Every body likes to see waveforms right, so here they are.Now I left the best bit for dessert, as you do !The SMPS is now.... completely.... SILENT ! I don't mean to say "more quiet", or " a lot more quiet", or "whisper quiet"... no, it is become absolutely silent, nothing to be heard what so ever ! I didn't quit expect that ! Was as shocked as I was surprised and pleased !I left it running for a fair bit of time, as I was taking measurements with the DMM and scope on all the rails... but it remained quiet. Powered it off after I had finished testing all the rails. Some time later I powered it back up again, thinking I might have just gotten lucky the first time, and that the noise would reappear.. but it did not !So.... my main project with this scope was to precisely use it as a test bed to investigate the SMPS whine, but now that said whine has suddenly vanished... well !!! I think I might keep it anyway, for the time being at least, to get some repair experience. So I still intend on giving a shot at fixing the remaining issues with this scope.So... was it the FET or the new caps that cured the whine ? No idea ! But it sure motivates me to do the long overdue recap on the SMPS of my 2232 ! When I fixed its SMPS last summer, after it blew, I was happy enough that I managed to get it back up and running (was overwhelmed and clueless, so thanks to the guys who helped me back then !), so I didn't feel like messing any more with it... I needed a rest ! LOLI think now is a good time to recap it :-)Also, worth noting : I noticed that the 2232 SMPS was unusually quiet and much quicker to go to near silence, than it used to be. Took it say 2 minutes to quiet down, versus maybe 15 or 20 minutes usually ! Only thing I can think of, is that last night when I used it, it was really, really very hot here !So this is consistent with Tautech's supposition that the whine might be related to a warm up/temperature phenomenon. Based on what happened with the 2215, I guess it's fair to say that it's either the caps and/or the FET that are involved. Given that I had already replaced the FET in the 2232, looks like the caps might be the culprit then ! Could still be the FET I guess, but I have ordered two of them. So if recapping the 2232 doesn't make it quiet, I might try replacing the (new but different model) FET, with the same I used in the 2215. So some more experiments to come !Some pics and straight to bed

author: tautech
author_rank: Super Contributor
timestamp: July 03, 2018, 09:47:36 pm
content: Great outcome Vince, congrats.Of course it makes perfect sense to replace that MOSFET with a modern equivalent especially to get lower Rds ON and subsequently much lower losses and heat byproduct.The only thing else I would do is to bring that -8V rail exactly to spec as it was most likely when new.So much in a CRO is related to the voltage rails and such a littleshould have it behaving just like new.Look out 2232..........you're next ! !

author: Pete F
author_rank: Regular Contributor
timestamp: July 04, 2018, 03:55:22 am
content: Thanks Vince, I got directed to your thread and it's very timely. I have the same unit to repair, in my case it's blowing fuses. I can hear the high voltage starting but then the fuse blows. Unfortunately I don't have another oscilloscope to capture the start up. I don't want to waste too much time on it, but will try taking out the mosfet to isolate the output and enable the pwm area to be checked.Did yours have that small PCB shield on the mosfet? I thought the whole method of mounting, with the thermal washer in between was an especially crap design!

author: Pete F
author_rank: Regular Contributor
timestamp: July 04, 2018, 04:26:13 am
content: Ok, the mosfet Q933 is blown, any idea what it is? IRF820?Just checking to see if that's the only issue or whether something else took it out.

author: Vince
author_rank: Super Contributor
timestamp: July 04, 2018, 06:26:58 pm
content: Quote from: tautechOK... I just adjusted it, see picture, not lying !My original measurements I did with my MX 54C, which is 0.05% +2D, not my best meter. To adjust it spot on well... I would need a fancy super accurate bench voltmeter... one day, but sadly no just yet. So instead I did the best I could, and grabbed my best DMM, a MX 56C, 0.025% +2, twice as good as the MX 54C.Still, with the "+ 2D" bit, right there we now that even if I adjust it spot on, it might possibly be still be 2mV off ! But well what can you do !Anyway, before adjusting anything, the MX 56C disagreed with the 54C : the former was more optimistic than the latter, deciding on 8,594 rather than 8.585. So only 6mV down, rather than 15. So I tweaked the trimmer... as I feared, it was very touchy and at first it made things way worse !That trimmer gives only coarse adjustment sadly. I eventually managed to get a 8,600V reading, but it's so touchy that I guess that just the act of handling the scope would make it deviate... let's be honest...But well, at least for the picture, it was for a brief moment spot on !I plan on getting on those popular and affordable Voltage reference from these people :http://www.voltagestandard.com/It would be a good start and allow me to check all my DMMs (I have over a dozen of them... I think I grew a fetish for these little things, just like I did for CRO's !) , until I can afford a precision bench meter.

author: Vince
author_rank: Super Contributor
timestamp: July 04, 2018, 06:50:08 pm
content: Quote from: Pete F on July 04, 2018, 03:55:22 amHi Pete,Did you open a thread somewhere to discuss your repair, so I can post there ? Link please !But to get you started I will answer your first questions here.First, I encourage you to read the present topic, only two pages. It will answer most of your questions.- No other scope : do'nt worry, you probably don't need it to get your scope back up and running. I used mine because well, I like to see what's going on and learn from my repairs, but it was not strictly necessary. You just need a decent DMM and a lab power supply.- as you I describe in the present topic, the very first thing you need to do is to unplug the regulator board, and power the scope/inverter directly from your lab power supply. You will need to set it at 43V and limit the current to something like 750mA, that will do. The scope never draws more than this. This way you will see if the scope is working and the problems limlited to the regulator board. From experience and that of others... most likely the scope survived and only the regulator board needs fixing, but of course YMMV so don't assume anything, just diagnose methodically. The reason for the scope surviving is that the reg board has en efficient crow bar... saves your bacon.- As a start, let's assume the scope is good and only the regulator board is affected. You can now reconnect the reg board, but of course only the mains terminal, and leave the DC output unconnected. This way the scope is not powered, only the reg board is, and you can now troubleshoot said board, again, methodically...- Before you plug the reg board, of course do all static checks first ! Look for any signs of damage do the FET blowing (or else...) : burnt components etc.When my 2232 blew/shorted its FET, half the regulator circuitry blew with it ! .. because basically it dumped the mains into the low voltage PWM circuitry, via the gate of the FET. So had to replace quite a lot of components. So spend a lot of time checking everything visually, then all passive and active components with your DMM, lifting legs where necessary so as to get a reliable measurement.- FET type : you say you can't identify the FET on your board ?! Boy it must have suffered really bad then !The FET type is not critical. On my 2215 scope it happens to be an IRF820, but the performance (RDSon/losses) is extremely poor compared to newer parts. So don't try to buy a new IRF820 (assuming they are still available, don't know), just get a better part from whatever supplier you use. As for me, as I explained a short while ago, I picked one at random using a parametric search, and works just fine. So at least you know this one will do the job, but many more will work just as well...- PCB shield on the FET : yeah as I mentionned, mine has this little thingie as well, see picture below.So to sum it up the very first thing to do is unplug/pull out the regulator board and power the scope/inverter directly from a lab power supply. Then report ... but on your own thread (will meet you there) not here please, I have enough on my plate with my own very sick 2215 !

author: Vince
author_rank: Super Contributor
timestamp: July 04, 2018, 09:40:54 pm
content: Recapping : oops, forgot to talk about the B Sweep board recap !There is one single electrolytic cap on that board, buried at the very bottom of it, not very accessible, not with my big fingers any way... was a pain in the butt to replace.At first I got suspicious/worried because up close, that cap looked like a bodge mod ?! I mean, it has super long leads and is soldered on existing pads, doesn't have pads of its own. So I was suspicious ! Turns out it's indeed a bodge but.. a genuine Tek one !On the schematic, one can see this cap ( C659) is there, it does exist... however when you look at the board view... they clearly forgot to route it !!!You can clearly see that they modified the board view by hand to add that cap ! LOLThe real thing on the PCB matches exactly what's on the board view, so I feel relieved... it's an intended mod, not some random hack from some previous owner. This only goes to illustrate Floobydust comments, when he said that this scope was rushed to market/immature...Another example : again on this alternate sweep board. The solder joints on the COMPONENT side of pretty much any IC, look horrible at best ! I managed a decent close up picture of one of these IC, as an example. Look for yourself ! Terrible eh ? Most pins have barely any solder at all on them.. and many of them are NOT connected to anything on the track/under side of the PCB, so no savior to be expected there ! One of the pins even looks corroded to me ?! The last one on the far right. I don't know where that corrosion might have come though ! There is only that one lonely cap on the board, and it's at the very bottom, I don't see how it could have spread/vented its electrolyte this far up the board ?!So I think this really motivates me to desolder that board (27 pins in one row, double sided... yike, will be "fun") so I can have good access to it and redo all the joint on all these ICs. I already have some connectors to solder to the board, ordered them along with the caps. Might solve my "dark spot" problem when delayed sweep is enabled. However... after fiddling with the scope some more... I think I have bigger problems to worry about that this dark spot ! The MAIN time base is playing up ! Well, I do'nt think the TB itself is at fault, but on many sweep speed settings, the trace just disappears ! Sometimes fiddling with the brightness control brings them back , somehow ! Trouble is that it all seem random, inconsistent... trace would fail to display at a given sweep speed...once, but 2 minutes later it might work just fine on the same setting ! So it's hard to trouble shoot random problems ! I have already cleaned and exercised the sweep switch(es) thoroughly. It switches very cleanly, I don't think there is anything wrong with it. But well, hardly an expert.. first time I have to work in this area of an analog scope.Anyway, must gut feeling is that it's this dreaded brightness auto-control feature that's playing up !I have to try and play some more with the scope until I can hopefully try to find a case/scenario where I can have a reliable/repeatable fault, so I have actually something tangible to chase/trouble-shoot ! Then hopefully once this is fixed, it will fix all the other seemingly random faults.... hopefully !At least now I know that what ever is wrong, it's not due to crappy power rails ! All new caps, DC levels are spot on and ripple is waaay within spec.So now I know I have a "real" problem to investigate.To be honest this auto-brightness feature looks such a pain to understand, I am not sure I will have the courage to dig into the subject far and long enough to get to the bottom of it... I will try, so as to learn a little something about it, but I am not so sure I will be able to fix it....For now, bed time...

author: Pete F
author_rank: Regular Contributor
timestamp: July 05, 2018, 01:08:18 am
content: Quote from: Vince on July 04, 2018, 06:50:08 pmI didn't start a thread on my repair, I didn't see the point. If somebody is searching for this information in future they can find it all here.Did you in fact read what I posted here? Shortly after the first question I posted the answer. The fault is a blown mosfet Q933. I believe it is an IRF820, so some more have been ordered (they are cheap so ordered some spares in case there's still an issue that caused it to fail). I have checked through the board as best I can and can't see any other obvious failures at this stage. The arrangement for mounting the mosfet is without doubt the most terrible design for that that I have ever seen. Looking at the evidence I suspect what may have happened is some condensation or other contamination has caused a short between that stupid little shielding PCB and the mosfet itself. When it failed there was smoke, crackling noise etc, yet no obvious signs on the components. Most strange. However the copper on the PCB seems to be eroded, so I believe it's tracked to there, eroded the copper and eventually caused an outright failure of the mosfet, as 'lectricity was going places it was never supposed to go! The proof will however be once the replacement was installed. When I was doing this type of work for my occupation I'd always like to satisfy myself as to WHY a component failed and not just WHAT component failed. It may have taken a bit longer but I very rarely got any jobs returning

author: Vince
author_rank: Super Contributor
timestamp: July 05, 2018, 05:36:50 am
content: Quote from: Pete F on July 05, 2018, 01:08:18 amYep I read that !But all you said was that you found that the FET was blown. You didn't say that you actually had found the root cause of the problem, nor what other components may have been damaged. So it was not clear whether you wanted any more help to take it further 'till the scope is actually fixed and running, or if you were happy to just stop there.Now I know !

author: Pete F
author_rank: Regular Contributor
timestamp: July 05, 2018, 06:51:53 am
content: Yes I was happy that the mosfet was the only issue. The graphics on it had faded so it was difficult to read, in the end I just ordered a new IRF820, and it seems to be running ok. I replaced the 2 main electrolytics on that board too, simply because the original ones were old. I'll leave it running on soak for a while to make sure it doesn't poop itself again.It still has a switch that is dirty for the 1/1+2/2 channels. I'd tried cleaning it with spray but it look like I will need to get more serious with it. I may as well go through the functions and fix little annoying things like that to repair them while it's open.I was ready to literally throw this in the bin, but it was dark and raining at the time, so it sat inside. Luckily the next day I decided to give it another chance and have a look if a repair was reasonably possible and practical. The total cost was A$1.50 but I decided to buy some extras so let's call it $5 for the parts and fuses. Not too bad to get it running again

author: Pete F
author_rank: Regular Contributor
timestamp: July 05, 2018, 07:10:41 am
content: Ok that channel switch finished up cleaning up ok. I have one faulty probe, so I'll need to get another one tomorrow, but other than that it all now seems to be working correctly.Good luck with yours.

author: Vince
author_rank: Super Contributor
timestamp: July 05, 2018, 04:22:52 pm
content: Quote from: Pete F on July 05, 2018, 06:51:53 amOK OK... I understand better now. At first you said it was "blown", then " I can't read the part number on it"... so I assumed the FET really blew or overheated badly, and its case either cracked or popped, or the ink melted... which is why I thought that the rgulator board suffered a catastrophic failure and that therefore, like happened in my 2232, half of the board need to be replaced ! But your latest comments look like the FET failed OPEN, not shorted, so yeah that'(s good luck as the FET didn't bring anything down with it...QuoteYeah, always worth a shot, you never know your luckMine didn't even power up, and it was all due to a tiny 10 cents Zener diode on that regulator board ! 10 cents and it was back to life !Well of course I still have other issues t fix now, but the show-stopper one has been fixed quickly and very cheaply.

author: Pete F
author_rank: Regular Contributor
timestamp: July 06, 2018, 01:32:39 am
content: To be good in repair never assume anything, always keep an open mind, even if you my think something is obviousThe MOSFET failed short circuit, hence why it was blowing fuses. Had it failed open circuit the circuit wouldn't have power up. It's why I pulled that out to isolate it, then tested it to find it was a short and I didn't need to look for the fault, it was in my hand. Then just test the (now isolated circuit) to see if everything else seemed to look ok.

author: Pete F
author_rank: Regular Contributor
timestamp: July 06, 2018, 05:02:58 am
content: Well, my gloat was short lived! The unit failed againI just turned it on to look at something quickly, and saw it fail.I came into this thread having mentioned my failed 2215 in the Test Instruments section, where I was looking for a modern DSO to replace this. As I said there I was a bit reluctant to start spending too much time with this, as it was at the end of its design life. What tends to happen is that the reliability goes down, sometimes to the point where it can become a project in itself. While I’m no longer a professional in this field, I still approach it as if I was, and it’s not a hobby for me. I have a lot of things to do and this is just a tool.Having said that, it seems it’s not worth just throwing it away, and having gone this far I may as well look at the second fault and see if I can find it. I won’t get a chance to look at it until next week but it sounded as if the PWM was oscillating but the transformer was very noisy and the power supply apparently not making voltage. The fact the transformer was noisy means the MOSFET is ok, but it could be something in the reg section. The first thing I’ll try is to replace the original caps (esp the 100 um) cap, as it’s possible that has failed in its early life. The brand was some rubbish I’d never heard of, so it would not surprise me if that was sketchy. If that’s not it, I’ll need to diagnose the issue without wasting too much more time on it. I hate it when tools start giving issues!

author: Vince
author_rank: Super Contributor
timestamp: July 06, 2018, 02:42:51 pm
content: Oh no, don't throw it away !Just send it to me, rather !Too bad.. .shipping cost make is uneconomical.Would be a tragedy when 99% of it's parts are still good and could help other people fix there scope ! At least you could sell it for parts on Ebay, it would make someone happy for sure !But I think yo might better off keeping it : as you said your scope is a tool not a hobby. So having a backup scope (once you do get a DSO) will avoid any downtime when/should the DSO fail. The peace of mind of having a backup scope is well worth the few bucks and a few ours fixing it !So, it fell apart again... meaning maybe it's time to dig further and do as I suggested earlier. Pull the regulator board and power the scope/inverter directly from a lab power supply, 43V and current limited to no more than 1Amp, and let it run for a while.This way you will immediately see where the root cause of the problem lies : pre-reg board, or downstream (inverter of secondary side of the scope).I think trying to bypass this (very quick and easy) step will just make you waste more time than necessary.Divide and conquer. Take the regulator board out of the equation to simplify and speed the troubleshooting !Also, look what I just read on TekScope ! Someone posted this old service bulletin that Tek issued about the 2215 !http://www.hakanh.com/dl/docs/hardtofind/SUP3010.pdfThey admit that they did a big mistake that causes the CRT to die/wear out very prematurely, causing a dim trace at fast sweep speeds, in a very short amount of time ! They notified all US customers about it, with a free CRT replacement for any scope brought to their service centers, no less. Howevr for non-US customers, no steps where taken to ensure that all scopes where fixed.Just checked mine, yep, its serial number is smack in the middle of the affected range, and nope, it has NOT bee modified/fixed ! ARRRRRRGH ! Too late now, nothing will bring the filament from the dead.I have not paid particular attention to the trace brightness at full sweep speed, but when I do and I find it's way too dim... at least I know that it's not worth waiting time troubleshooting something that just can't be fixed !This obviously once again illustrates Floobydust's plentyful experience of these scopes back in the day : "immature, rushed to market...."Yeah, there is decidedly something going on with these 2215... definitely one I will not buy again... you live and learn !Still, at least it's a great scope to get some repair experience, because repairs it needs plenty of ! LOL

author: Pete F
author_rank: Regular Contributor
timestamp: July 06, 2018, 04:40:06 pm
content: Yes I’m fairly sure the issue is restricted to that board, so no need to isolate it. It’s quite likely there are other latent faults with the unit, but that can lie thereI’ll know more next week when I have an opportunity to look more closely at it.

author: Vince
author_rank: Super Contributor
timestamp: July 14, 2018, 10:10:07 pm
content: Hmmmm... just happened to watch the latest video from the repair blog " Artifact Electronics ", he is currently working on an old " TRS-80 " 8 bit computer, is fixing many issues with it, and oh, at 7 minutes and 40 seconds, starts an interesting bit !https://youtu.be/lmMi0KvUebw?t=460Yep... despite this machine having nothing to do with an old 22XX Tek scope... this old computer has also an SMPS doing the same horrible high-pitch noise.... and the most interesting bit : as far as I understand, looks like the culprit was... a leaky/bad electrolytic cap on the secondary side of the power supply. He replaced just the one, and the noise went away !So... looks like the recap I just did on my 2215 SMPS might indeed be responsible for fixing this horrible noise ! So definitely well motivated to recap the SMPS on my noisy 2232, no question about it ! I can't believe that there was so much discussion about this noise in these old Tek scopes, theories of transformers, FETs, resonance, and what not... when probably in many cases at least, all that was wrong was, again, the dreaded crappy old electrolytic caps ?!It's now so cheap to get top quality caps on-line, of any value and voltage rating you want... I am starting to think that some people are right... just recap the SMPS no matter what. Can only make things better, and in any case will be good preventative maintenance because they would cause issues later down the line any way, sooner or later. I think it was David Hess last summer who was suggesting me to recap the SMPS of my 2232 from the get go. Will do soon, and if that fixes this horrible high-pitch noise... will apologize to him for not listening ! LOL Admittedly back then, I had enough problems with that scope, and was so inexperienced that my plate was full enough... adding a recap to the list was a bit too much for me back then. Not any more !Okay... have not worked at all on the 2215 lately, busy with work and things. Not been inactive though : spent quite some time studying the schematics and reading up some of the "Theory of Operation" sections in the manual. I am not so much in the dark any more as to the weird symptoms I am seeing. Just need some time to get to the workbench and fiddle with the scope. but I am hopeful, it may not be as lost a case as I thought... crossing fingers !Sorry for being vague, will be much more concrete once I have managed to actually work on the scope and report !

author: tautech
author_rank: Super Contributor
timestamp: July 14, 2018, 11:06:16 pm
content: Yes, it's not until you start playing with boost/buck magnetics that you fully comprehend how sensitive they can be to component variations.As I'm sure you'll find with your 2232 jsut an out of spec cap can force them into an unhappy mode of operation.Some of the e-cap changes can be quite subtle or just the additional current load of slightly leaky remote bulk caps somewhere else in an instrument.I used to think just reasonable accuracy capacitance measurements were enough to find the culprits and generally it is, but not 100%. Sometimes cap leakage is voltage dependent and there's been great discussion in the forum lately stemming from a LV cap tester from Mr Carlsons lab which of course might be OK for the bulk of testing we do but by no means all scenarios. Joe Smith also did some good testing of HV cap leakage by sweeping cap voltages to listed max and measuring leakage right through the working range. Pretty simple really and then compare against datasheet spec.However, a competent 'repairman/technician' shouldn't by default be taking a shotgun approach and have some sort of ESR testing means to properly understand cap failure and know just by looking whether caps should be low ESR or not.Many years back knowing what place SMD would play in our futures I splashed out on the best pair of SMD Smart Tweezers I could afford (and other purchases were put on hold) and they've rewarded me with reliable ESR measurements that have allowed me to identify many dud caps that don't show any signs of degradation.The $$ hurt at the time but now knowing just how capable they are I would replace them in an instant !

author: Vince
author_rank: Super Contributor
timestamp: July 15, 2018, 12:02:36 pm
content: Hi Tautech,Yes, ESR meter and HV leakage testers are on my list ! ESR short term, HV leakage mid-term... especially as I would like to design/build my own as it seems quite simple, so would be a good excuse to design something, and small enough a project that it would probably actually get completed, ahem...ESR wise, my budget is limited so I was thinking of this 100 bucks DER 5000 hand-held LCR meter. For the price, I think its by far the best bang for the buck I can get, feature and engineering quality wise, and of course it would do much more than just ESR. With its 4 wire design/construction, it will be able to measure tiny pF range caps much more accurately than DMM's, as well as accurate low ohms measurements which I also need/want to be able to do. Still, 100 bucks is still a little steep right now, and so to get me going very quickly I am now on the verge of buying one of these popular 10/20 bucks little kit ATmega based "do it all" component testers, as they also do ESR and do a decent job at it apparently. Will also help me sort the gazillion of components I have recently salvaged, after "processing" 5 large boxes of boards.Been meaning to buy this little tester for some time now...but somehow always finding good excuses not to... but I think I need to get my priorities straight, or else I will never get it : In the past few weeks I have felt weak and eventually spent some money for yet some more old instruments which in all honesty I did not really need... like this 2215 to start with, which cost me 60 Euros shipped. So if I don't get my priorities right, I will just pile up old gear yet not even have the basic test instruments I need. I need to balance things ! I can't justify spending money on old gear yet pretend I don't even have just 20 bucks for that little component tester.... isn't it.Would need to make sure it can test ESR in-circuit though, or else it won't be much use. Still, I would still get one I think, to help me test/sort all my components. As far as I understand, an ESR meter basically is just an AC ohm-meter with a signal amplitude of a hundred mV or so, low enough to make sure it won't turn on/be "contaminated" by PN junctions, even old low drop 0.25V germanium diodes. Then it's up to you to implement / design it the way you like...HV leakage tester wise... yes I definitely intend on getting one, especially as I am getting more and more fond of these old glowing Tek scopes, and even other tube based test gear ! Recently in the local ads I fell in love with an old Metrix 620 "LCR meter" / impedance bridge ! With its magic eye tube, and big black Bakelite knobs and lovely, thick engraved stainless steel dials that just ooze style and quality... I just couldn't resist, at only 35 Euros (and a seller willing to ship, for a change !), when this instrument usually sells for 150 Euros or more... I had to have it !I know... when I bought my Tek 317 scope I promised myself it would be my first and last piece of tube equipment... and that therefore, for example, I would not invest in a tube tester. That was a year ago.... a year later, I am so in love with that old Tek scope, such a joy to look at and operate, both inside and out... I feel an addiction growing fast ! I now can't help but look at every glowing Tek ad I spot in the "local"/French ads ! " Luckily " so far, they have all been way too far away from me (usually at the other end of the country...) to make it worth the trip, both from a financial point of view (gas is horribly expensive over here, any trip over 50kms starts getting costly...), as well as from a practical point of view (my right leg hurts badly after only 45 minutes of driving, and I must stop).But.... the other day I found a 535A scope for only 50 Euros and for once, it was not too far... though not really next door either : 200kms. So I e-mailed the guy to see if he might have the opportunity to drive part of the way for some personal or business trip he may have planned in the near future... but no answer as of now. Been a couple weeks.... So looks like even this one, will escape me ! LOLNo really it's a pain. The old 500 Tek scopes do pop up regularly over here, maybe one every couple of weeks of so, country-wide, but they are never close enough to me, and of course the sellers refuse to ship them ! Mostly because well... even if they bothered packing it, the resulting parcel would exceed the weight limit and overall dimensions that the mainstream/affordable transporters allow : 30kg max, and only 150cm for the sum of the 3 dimensions. So a 50cm cube for example... now try fitting a 500 scope, and all required packing material, into such a tiny footprint....At least the Metrix 620 was small and light enough that shipping could be reasonably considered....Anyway, digressing again sorry.. you know me !So yes, a HV leakage tester is definitely on my list. It's not as urgent as an ESR meter though, and I am not aware of new/off the shelf testers (though I didn't really search that hard to be honest ...). I would love one of these period/vintage testers, but hard to come by, too expensive, and very bulky...Given that the operating principle is simple, from what I understand (just apply desired voltage and measure/display the current using whatever form of display you like... magic eye tube, galvanometer, whatever...)... I would love to design my own... Currents involved are very low anyway, so shouldn't be too difficult to design a suitable HV supply... should be fairly easy and not take too much space at all. Should be able to all fit in a more compact/"bench friendly" enclosure than the old tube based testers... I would think. So this little project quite appeals to me...As for Paul's LV leakage tester.... it kinda leaves me confused to say the least !I love this guy, been subscribed to his channel for a while now, been watching every single video in his catalog. I like the design/engineering bias of his videos, and from what I understand he is an actual design engineer, so I give him credit and enjoy all the advice and tips he gives in his videos..... however, when he presented his tester the other day, I was at a loss : HOW can you test the behavior of a component, cap or anything else, at say 600V.... unless you actually SUBJECT it to that voltage ?!From what I understand, it kinda "works" in practice, because he mostly tests 60 year old caps, so have had enough time to degrade so much that they would leak a measurable current even at only 2 or 5% of their operating voltage (especially since, AIUI, his device can measure/detect extremely low currents)... so by extrapolation, reasonable extrapolation, but extrapolation only none the less, we can safely assume that if it leaks at say 5V... you bloody can bet it will leak like mad when subjected to its multi-hundred volts operating voltage. OK, I am fine with that...But if the cap is not that old, is only at the beginning of its deteriorating process, and only starts to leak at say 90 or 95% of its operating voltage.... several hundreds volts then.... the LV tester will not register any significant current and declare the cap good, when it is not...So I think this LV meter is great as an INDICATOR, to help find very/blatantly faulty caps, and would be plenty good enough in practice, when working on really old caps/instruments, and I understand Paul did a lot of testing to confirm this.... but still, it's only an indicator, not an actual / reliable test of how the cap performs at its actual operating HV...Also... the only reason Paul designed a LV leakage tester, from what I recall, is that he thought people might get zapped when using old/vintage HV testers, by accidentally touching the test leads/jacks, or forgetting to discharge the cap before handling it after performing the test. Well... I mean, if you can't even watch your fingers and think, when you are merely testing a cap on your bench... how will you survive the process of restoring/fixing the tube piece of gear that you are trying to fix, given it has HV absolutely all over the place, if you can't even watch where you put your fingers and pay attention to your own safety ?!Hell, how can you fix ANY mains powered piece of gear, even modern stuff... given that most of them have a 240V SMPS hence with 340Vdc or so, across the main filter cap ?!I understand Paul is from the US where every video over there, starts with "do it at your own risk, I can't be held responsible for your electrocution blah blah blah", but come on... if you work on HV equipment, well... you should not do it unless you know what you are doing ! You are not some kid that needs safe guards and babying, you are an adult who knowingly chose to work on HV stuff !Of course I am not saying we should play with fire needlessly, so I am all for making HV testers as safe as they possibly can be, by minimizing exposure to HV as much as possible, through careful mechanical and electrical design, just like a good DMM does... but at the end of the day, if you want to test a cap at its HV operating voltage, well one way or another you will have to produce said HV and deal with it !What next ? An insulation tester that will test motor winding insulation at 10V instead of 1,500 Volts ?!...And what should we do about all these glowing Tek scopes ? Should there be a law that forbids selling them to "unauthorized" individuals ? I mean, ANY of these scopes have HV not just inside of course, butEXPOSED ON THE FRONT PANELas well !!!! I mean, the probe calibrator output can be adjusted at the flick of a knob to produce no less than 100V, for starters !! Then, among the few 4mm binding posts that populate the right edge of these scopes, you will find the sawtooth output from the sweep section, which ramps up to 175V or so !!! And this binding post is literally at your finger tips when you operate the sweep knob ! So people could get zapped easily just by OPERATING the scope, not even by opening it to mess inside of it !Let's be reasonable...Again, I love Paul's blog and every bit of design/engineering comments he brings to his videos.. but in the particular case of this LV tester, I really don't understand...A great little tool, a help, an indicator, good for most practical restoration purposes of old gear, I don't doubt it, he tested it extensively and has massive experience restoring Vintage gear and dealing with these old caps.... but an actual, indisputable test instrument... it's too much of a stretch in my viewHell instead of babbling here I guess I rather ought to work on the scope !

author: tautech
author_rank: Super Contributor
timestamp: July 15, 2018, 08:38:42 pm
content: Vince, you have a good understanding of what's required and enough experience to help you interpret test results.I know a couple ppl with the $20 tester and for starters it's a good tool and good value. For me, well they came out after I got SMD Smart Tweezers that measure into many K's of uF and down into pF all with ESR so I've never been temped to get one for cap testing. Active components and identification, well yes the $20 tester can do that too so some added value there. The UK Peak products interest me too and I will probably get one of their active component testers before anything else....if I need one.Member Defpom is looking at building an HV cap tester kit and I've been watching his progress on YT but he's got some way to go with it just yet. His will go to 500V so could well be interesting once he polishes it to where it's available as a kit.He's also got a DER5000 that we see him use in videos but I haven't seen it be any more useful than my SMD tweezers.Anyways, it will be a sad day when we don't all yearn for more and better toys !

author: Vince
author_rank: Super Contributor
timestamp: July 15, 2018, 09:50:22 pm
content: Thanks for the tip on Defpom's project, will check it out...SMD tweezers yeah they look cool, but I think good ones still cost a fair bit, and for practical as tehy are, they can never compete with with a decent hand-held like the DER 5000 or whatever similar, if just because of lack of real estate to fit hardware in them, as well as buttons and a decent size display on them.Ideally I would want both SMD tweezers, because quite practical as you said, and sufficient for many purposes.. but also a DER 5000. But a decent SMD tweezers would cost at least as much as the DER, if not twice as much. So I can't justify tweezersThere is hope though : from what I recall, the DER can be found either standalone, "naked", or in a little carry case with some accessories... which include tweezers you can plug into the DER !I think I will probably follow this path...

author: tautech
author_rank: Super Contributor
timestamp: July 15, 2018, 10:43:59 pm
content: Quote from: Vince on July 15, 2018, 09:50:22 pmYou'll never know (and I didn't) until you own a set !Only when the leads of a component are more that 25mm apart do you have trouble connecting to them but you can extend the leads...... SMD tweezers, well I use them more than a DMM or scope as they make finding faulty passives much much faster. On a small PCB I can whizz overallpassives in less than half the time of a DMM and without need to change ranges for all passives. Capacitance and ESR measurements on the fly and for diodes, it's much faster too and gives indication of the cathode side with a single contact......no swapping probes.I use them for everything, SMD in tiny tiny sizes and TH to as big as I can comfortably spread the legs.Mine are old ST-3 but if/when I replace them I will get the TOL set ST5S.http://www.smarttweezers.com/st5s/Yes, they cost as much as a new DSO......but I use them more than I ever thought possible when I first got them.And I forgot.... L measurements too !

author: Vince
author_rank: Super Contributor
timestamp: July 15, 2018, 11:10:25 pm
content: Sounds good but just not in my price range !And this tiny, minucule display... would need new improved bionic eyeballsBut if I could afford it yeah, why not....Might get cheap ones just to see if I can get used to handling such an instrument, and watching such a tiny display... but not any time soon that's for sure...

author: james_s
author_rank: Super Contributor
timestamp: July 18, 2018, 12:44:38 am
content: I really like those Tek scopes of that era. I remember lusting over them in catalogs when I was a kid, but they were way beyond what I could afford at the time. Instead I found a Tek 532A at a garage sale eventually, that was very exciting, and it doubled as a heater for my bedroom.

author: Vince
author_rank: Super Contributor
timestamp: July 19, 2018, 08:54:05 pm
content: Yeah they are good heaters indeed !Hopefully I will have finished putting mine back together by this winter so I can play with it while heating the lab at the same timeI found these scopes so gorgeous, such masterpieces, that I am truly amazed that one can get get them for so cheap ! It's so rare theses days to find good stuff that's cheap ! So I can't resist them... I feel weak every time I see one for sale !There is so much old ugly crappy instruments on Ebay that sell for fortunes, that I can't understand how these beautiful glowing Tek scopes have managed to escape the speculators ! This may not last for long though, who knows... so that's another reason why I try to get those which happen to be at my reach : I try to get them WHILE I CAN ! Maybe one day the market will decide suddenly that they are "fashionable" and prices will start becoming silly, and I won't be able to afford them any more.So I am glad I have managed to get at least one example, thanks to my little modest 317 model. Needless to say I will treat it well and cherish it...If I can get a couple more of these scopes, that would be cool, but I have at least one so I am "safe"... I now own a little piece of history, nobody can take it away from me.....

author: tautech
author_rank: Super Contributor
timestamp: July 19, 2018, 08:59:12 pm
content: If you lust after early Teks, check out threads by Martin.M.This was his first post:https://www.eevblog.com/forum/testgear/vintage-tek-restoration-pictures-by-martin/msg589744/#msg589744

author: Vince
author_rank: Super Contributor
timestamp: July 19, 2018, 09:12:58 pm
content: Yeah you steered me to his topic a year ago when I bought my 317 last summer, took me some time to read it all, but was worth it

author: james_s
author_rank: Super Contributor
timestamp: July 19, 2018, 10:56:47 pm
content: Quote from: Vince on July 19, 2018, 08:54:05 pmI finally gave mine away a year or two ago simply because it was so big and bulky and it was only a 10-15MHz scope. When I have a 1GHz Tek DSO on my bench and a 100MHz "portable" Tek 340 it's hard to justify keeping a gigantic antique around even though it is totally cool. My space is limited and I have test equipment primarily to use. My bench isn't a museum.

author: Pete F
author_rank: Regular Contributor
timestamp: July 20, 2018, 05:39:16 am
content: In fairness James, I feel the analogue oscilloscopes still have their place. I left the industry well before anything like the modern DSOs were available and have just been exposed to them for the first time. Obviously I appreciate some brands will be easier to use than others, but so far my experience with the DSO I have is it’s nowhere near as fast to use for fault finding and general signal tracing as my old 2215 or similar. There’s no doubting the power of the modern DSOs, even ones costing just a few hundred dollars, but it seems to me that power comes with certain trade offs.My 2215 requires a new high voltage module, and I’ll certainly be fitting one when one comes up at a realistic price. In my opinion the two seem to compliment each other. I’m not sure I would be wanting to go too much earlier than the 2213/2215 era etc though. They seem basic enough to be realistically repairable, and the general service information is excellent by modern standards. They are from an era where we repaired things rather than adding to landfill

author: Vince
author_rank: Super Contributor
timestamp: July 20, 2018, 02:56:32 pm
content: Quote from: james_sAh well yes of course, if you run a business and every single penny and cubic feet must be justified by how much money it will get you in return.. then yes a glowing Tek is not a good idea....But I am a hobbyist, the only justification I require o buy stuff is... that I like the instrument and can afford it and I have space for it. Makes things simpler indeed !Still, these old Teks still, in all objectivity, are still better than some brand new digital scopes ! Glowings Teks sell usually between "free, just come and pick it up", to 50 bucks. For 50 bucks you don't have that much of brand new DSO, not even the crappiest,most bottom of the line of the most obscure Chinese brand, say Owon or whatever. In the 50 bucks range all you can get is one of those kit DSO whic are just a tiny palm sized PCB wit ha couple push buttons and a tiny stamp size LCD, with 100kHz of B/W... you see the kind :https://www.ebay.fr/itm/DSO138-2-4-TFT-Digital-Oscilloscope-Acrylic-Case-DIY-Kit-SMD-Soldered-New-R2C0E/223067764502?hash=item33efdff716:g:LxoAAOSwaLJbTHH2Or this one, closer to 50 Euros.. you do get a crappy plastic case with this one, and even a BNC connector for the input, woohoo luxury !https://www.ebay.fr/itm/JYE-Tech-Dso-COQUE-Digital-Oscilloscope-Kit-15001-200KHz-DSO150-Flux-Atelier/123259803899?hash=item1cb2db58fb:g:8DkAAOSwWupa-q9-In all objectivity, even my 1959 Vintage Tek 317, o orders of magnitude better than these DSO... even though they are 60 year younger, literally.And my 317, even back then was hardly the best performing scope that Tek had on sale... it was just a modest field/service scope...Still, at least :- it has a proper case and use interface that's actually usable and even pleasing to use, and look at as well. Form and function, why choose when you can have bothIt's- Bandwidth, at 10MHz, is literally a couple orders of magnitude higher.- Screen/viewable area is much larger, even though it's got a tiny 3 inch tube, not even the large 5" tube of the more common glowing Teks- Proper H/W trigger- Wide input dynamic range- Proper attenuator / pre-map front-end section- probe calibrator- has a built-in power supply, just plug it to the wall.- can be operated with one hand, it's rock stable.Then if you compare it to top of the line 500 scope, the advantages just get better, with a large 5" tube, often with a delayed time base, and 100MHz B/W, and plug-ins to do this and that for specialized work.It's incredible to think that even current Tek (or other major brand) entry level scopes, 60 years later, still don't offer 100MHz B/W as standard, making them effectively less capable than some of these old glowing Teks. It's mind boggling when you think about it......Anyway, I am fortunate enough, being a hobbyist, to be able to buy old stuff just because I like it, no need to justify it. No need to choose between old or new, why not get both if that makes me happy...Most people around me, smoke. A quick calculus indicates that even a "normal"/average smoker, spends something like 5,000 Euros, that's in the order of 6,000 US dollars, to buy his cigarettes, an astronomical amount of money, scary.I don't smoke, so for 5 grand a year, each and every year (given than most smokers never quit) I could buy a tremendous number of old test gear... and spend some of the money to build a larger lab to host all these instruments.Even discarding "vintage" scopes, I would still keep both my analog scopes and DSO. They complement each other and the DSO will never be able to match an analog for ease of use and trace quality and "charm", dare I say... I don't want to choose between analog and digital, and I don't have to, so I will keep using and enjoying both...

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2018, 04:58:33 pm
content: I'm a hobbyist, but space is still at a premium. I only have so many rooms in my house and at this point all available space is pretty well used up. Getting something new means getting rid of something I already have, so I couldn't justify keeping a gigantic old scope around when I have other scopes, including a Tek 465B for times that analog is better. I'm glad some people like the old tube scopes well enough to keep them around though, the 532 is a work of art.

author: Vince
author_rank: Super Contributor
timestamp: July 20, 2018, 05:54:43 pm
content: Yeah I understand, space is everything... I only have two rooms, so the spare one is for the lab. A small 3x4meters room.That's why I fell in love with this 317 scope. Back then I only knew about the super big 500 series scopes, just like you I couldn't see myself keeping a huge instrument like this in my tiny lab. Then I came across this little 317 model in the local ads. Looked just as nice/cool/charming as any of the 500 series scopes, but was much smaller/manageable, an ideal compromise, and such a cute little thing !Couldn't resist, bought it....When the construction of my house will be completed, I will have a lot more room to devote to my hobby, so that's why I am now considering getting a couple 500 scopes as well, depending on opportunity.

author: Vince
author_rank: Super Contributor
timestamp: July 28, 2018, 12:34:33 am
content: Well.... this is the end !Tonight, felt like I had finally an ounce of motivation to work on the scope.... I tried to remove the alternate sweep board from the main board, so I could access it and redo most of the solder joints as it seems that not only the scope was rushed to market, but also the wave soldering machine Tek bought... or maybe the guy who set up the machine was not paid enough, or was drunk, I don't know....Anyway, this daughter board is no fun : vertically mounted, a single row of 27 pins, soldered directly to the main board, and all pads are double-sided.... I did my best. Wasted half the scope worth, in flux and solder wick. Underside was easy of course, but the access on the top side is not that great. Would not come off.Eventually fired up my crappy hot air station... board was out in no time, should have used it from the get go. But was too late : I guess I heated and wiggled the board too much, and for too long, when I first tried with the wick. So the board came out, but so did 9 plated vias with it ! Ohhhhh.... nooooooo...That's way beyond "economical repair", so I quit.Did fire up the scope without the board though, just to see what would happen ! I was not disappointed : Tek did things right, and without this board, the scope works just fine, everything is normal... just that nothing happens when you try to enable the delayed time base... of course !If anything, pulling this board helped in my diagnosis : one of the biggest issues was that the signal trace would disappear for any and all sweep speed below 0.5ms / DIV. Hint : the manual says that the auto-intensity feature actually kicks in ONLY for sweep speeds from 0.5ms and up ! What a coincidence ! LOLSo I figured maybe the signal trace is there, but the intensity is somehow turned all the way down by some odd mechanism/bug.... so I made the lab completely dark and yeah, I could see the trace ! And it was behaving normally, whatever the sweep speed.... just that I couldn't see it under normal lighting conditions !Well, removing the alternate sweep board somehow cured the problem ! I can now see the trace just fine at speeds below 0.5ms/DIV. It is still a bit dimmer than at higher sweep speeds, so there is still something that would need investigating... but the trace is now perfectly visible. Scope is actually usable now...So I think I will keep it any way... even without the delayed sweep, it's still a perfectly good scope. Hell there are 2200 scopes even lower spec than my disabled 2215 ! LOL I mean, there are 2200 models that don't even have a delayed time base to start with ! And some even have a lower bandwidth, 50 or even 20MHz ! So... my 2215 is still useful as a backup scope, or for when I want to make "risky" measurements, ahem...And the SMPS is completely silent now, so nice to use just because of that !!!So... that's it for this little 2215 ! Learned a lot while studying its schematics for hours, especially the delayed time base and auto-intensity circuitry.Delayed time bases are not longer this mysterious and magical thing any more ! It's actually quite simple... quite clever... it doesn't take much at all to implement this marvelous feature... every analog scope should come with that as standard !As for the rare auto-intensity feature found on this 2215, which was one of the main reasons I bought it, was curious about this feature... well I will have to join the bandwagon of those who said "never again, no more" ! LOL Yeah, it indeed just doesn't work that well, it's more of a pain than an asset ! And it just makes the intensity control circuitry twice as complicated as in any other scopes, with interactions with the focus control and sweeping... it's just a whole mess that's not worth it, in practice. So I have my answer now : YES, auto-intensity did exist on analog scopes.... but no it was not worth it and was happily and quickly dropped !So... this is the last time I attempt such a desoldering job... I will definitely invest in one of these popular Hakko desoldering guns. Hopefully this will save the life of the next such board I try to remove...I really need to stop spending money of old gear for a moment, and rather concentrate on improving my soldering gear and test equipment, so I can do a better job at fixing stuff... I feel I am just butchering stuff for now, with my cave man gear.Anyway, after getting side tracked by this 2215, I think I can now come back, at very long last, to finishing the restoration of my old 317 glowing Tek. Poor thing has been waiting for 7 months now ! Feeling ashamed....

author: tautech
author_rank: Super Contributor
timestamp: July 28, 2018, 12:50:14 am
content: It will nag you for years if you don't try to recover it !I'm sure you can given a little time to think about it and devise a cunning plan.Vias, who needs them anyway, isn't it only a 2 layer PCB ?Can you remove them from the pins and reinsert them ?Maybe replace the pins with a 90oheader set.Lots of ways to get yourself out of thislittlepickle.

author: particleman
author_rank: Regular Contributor
timestamp: July 28, 2018, 01:17:05 am
content: Mouser sells eyelets for plated through hole repair.https://www.mouser.com/Search/Refine.aspx?Keyword=keystone+eyelets

author: Vince
author_rank: Super Contributor
timestamp: July 28, 2018, 01:18:52 am
content: Hi Tautech,Well... I guess I have nothing to loose and could use this 2215 to practice PCB repairs ! LOL Why not... this scope was meant as a test bed to begin with any way, so let's extract as much "eduction" out of it as possible, eh ?!OK I might attempt to repair the PCB... Yes I can removed the 9 vias from the pins, and try to solder them back on.I have already (straight) headers ready to go on the main board. If I can't manage to stick the vias back into their holes, I could just discard them and just use a simple pad. The pins on the board would be enough to connect top and bottom sides anyway. Hell worse case, if I can't put pads back onto the PCB, I could just run a short piece of thin wire from the header pins, to the remains of the nearby tracks.Main problem though, would be physical access to the main board in order to do all this !I remove (again) the (main) sweep & amplifier board, that would improve things a lot I think.OK I might look into this...

author: Vince
author_rank: Super Contributor
timestamp: August 17, 2018, 09:12:58 pm
content: Alright.... Tautech, thanks for pushing me into repairing the broken pads/PCB... because once I had stopped crying, got some sleep, went to have another, calm look at the "situation" and well... it's not at all as bas as it seemed, plenty repairable !Out of 9 pads that got ripped/sticked to the daughter board connector pins... 6 were actually connected to nothing on the main PCB ! These were just lonely pads that served no purpose, other than helping with mechanical rigidity I mean, I guess. But there is already a plastic clip atop the board, that holds it to the SMPS shield anyway. So not too bothered by these pads, nothing to repair in fact.So 9 minus 6, that leaves us with 3 pads to repair on the main PCB... so let's look at those in detail... see picture : good news again !I don't even need to repair these pads (not equipped for that and access is not that great anyway, with the board mounted in the chassis), because the tracks coming off of these 3 pads, don't go very far until they reach a via ! So, all I need to do it solder a small one inch or so mod wire, into these via, then solder the other end straight to the header connector pins, once it's soldered to the main board... and it should work I would think !Before soldering the header connector to the main board, I had a good look at all the solder joints on the daughter board, and indeed most joints don't inspire a lot of confidence. Dull looking and with so little solder in them that I wonder if Tek was trying to save money on solder to make this bottom of the range scope even more profitable for them... maybe they ran a contest in the PCB workshop : the Tech that manages to set up his wave soldering machine to use as little solder as possible, gets a 10% salary increase ! LOLOne of the joints had so little solder that it hardly filled the hole in the PCB...Said joint was on some component that I had never seen before but that I assume must be a resistor of sorts, given its looks : a hollow mandrel with coloured dots, the size of a 1/4 W resistor, that looked like it belonged to a much older vintage, looked out of place in an '80's scope.. But.... according to the silk screen and the schematic, this thing (see pic) is actually a capacitor ?! Well, I learned something new todayI don't how they manage to make a capacitor out of a hollow mandrel ?! Do they wrap just a couple turns of thin film around it, so that the overall thickness is still "slim".. if so, I guess the values they can achieve with so little film wrapped no the mandrel can't go very far... 1nF tops ? A few hundred pF ?!Anyway, I went to start fixing the 3 broken pads, then tried to fit the header connector I had ordered the other day.... STOOOOP ! Header doesn't fit !Eh ?! Grrr ! Stupid me ! This old through hole scope, I just assumed the pin pitch on the board was the usual 0.1" , so ordered the usual 0.1" header to go with it. That will teach me ! Looks like the pitch on the board is exactly 50% large than the 0.1" connector. So I need to find something suitable... hoping it is still available.Grrr.... I was so persuaded that I would have the scope going again this evening... not !Getting closer anyway...See you in a bit, once/if I can source a suitable connector...

author: particleman
author_rank: Regular Contributor
timestamp: August 17, 2018, 09:24:42 pm
content: looked out of place in an '80's scope.. But.... according to the silk screen and the schematic, this thing (see pic) is actually a capacitor ?! Well, I learned something new todayThey are temperature compensating ceramic caps. Otherwise known as dogbones.

author: tautech
author_rank: Super Contributor
timestamp: August 17, 2018, 09:28:44 pm
content: Glad you were able to step back and take another look Vince.0.150" pitch for the header ? That used to be a common one.

author: Vince
author_rank: Super Contributor
timestamp: August 17, 2018, 09:42:37 pm
content: Quote from: particleman on August 17, 2018, 09:24:42 pmThanks !Will read up on that...I guess this explains their form factor then. Being skinny and hollow makes the body "track" ambient temperature more easily. Good airflow and low thermal mass.

author: james_s
author_rank: Super Contributor
timestamp: August 17, 2018, 09:59:54 pm
content: I wish I had an easier time staying skinny and hollow

author: Vince
author_rank: Super Contributor
timestamp: August 17, 2018, 10:06:10 pm
content: Quote from: tautech on August 17, 2018, 09:28:44 pmSadly for me it looks like is not so common anymore ?!I just looked at my two main/local suppliers here, TME and Farnell... none of them have anything suitable ! They do have a FEW 0.15" / 3.81mm pitch board to board connectors, but they are very bulky and weird looking, nothing to do with our thin low profile usual connectors.Had a look at mouser in the US, just out of curiosity (since I can't buy from them anyway, other than importing), and same as Farnell, all they have is this funky connector model :https://fr.farnell.com/hirose-hrs/fx30b-4p-3-81ds/connector-header-4pos-1row-3-81mm/dp/2451006I can't quite believe I am defeated by a bloody connector ?!I mean if I solder the board back to the main board, without connector, I won't be able to remove it at will to trouble shoot itr and work on it... because once it soldered to the scope, access is horrible and I won't be able to probe anything, never mind replace any component. The board and PCB traces almost survived being separated ONCE... they won't survive it twice or more, that's for sure. Not to mention the work/hassle it is to remove it, brrr... 27 pins in a single row, double sided, not fun...So... that's bad news. Now all I can do is solder it back and cross fingers that it still works and that the "dim" trace problem when the delayed time base is enabled, is not located on that little board...Decidedly, this 2215 is driving me nuts each step of the way ! :-/I can't believe I am in trouble just because of a bloody connector ! A silly little, humble connector !Come to think of it, I had the exact same problem when I repaired my 2232 last summer, if you remember ?! No of course you don't remember, just kidding !I had a bad connector, a wire to board connector, that connects the main board to the big digital board. Was impossible to find a replacement ! I posted on the forum with this specific request, and nobody could find one either ! Luckily I could get a way with it , by soldering the wires of the cable, directly to the digital board. The cable had a (removable) connector at te other end, on the main board, so the digital board could still be unplugged, phew.So, I guess that's now x2 22XX Tek scopes endangered by obsolete large pitch connectors ?! Starting to make me feel uneasy about these scopes... being at t eh mercy of such a futile little component, how frustrating !

author: tautech
author_rank: Super Contributor
timestamp: August 17, 2018, 10:11:31 pm
content: As most of the pins are for physical support could that be provided with a bracket/s allowing you to use only the pins that provide an electrical connection ?Frankenscope ?

author: james_s
author_rank: Super Contributor
timestamp: August 17, 2018, 10:13:50 pm
content: Maybe you could replace it with a more commonly available connector and solder that in with a little adapter board or separate wires? I always prefer to find the correct part but sometimes it just isn't readily available and a hack like that becomes excusable. This isn't a priceless collectible that has to stay original inside and out.

author: Vince
author_rank: Super Contributor
timestamp: August 17, 2018, 10:32:24 pm
content: thanks for the suggestions... sadly I don' think it would be worth the effort and experience. I mean doing an adapter board would cost money (I can't make PCB in house), and I would still have to find appropriately pitched connectors to solder on that adapter... at least on the mother board side. Yeah on the daughter board side of things, I could make do with individual wires, though I would still have 26 out of 27 of them to wire up ! Just looked at the schematic... there is only one single pin that's unused :-/Also, all this wiring would add a fair bit of stray capacitance and inductance, can't be a good thing. That why I liked the low profile header : very short, so very little perturbation introduced.I guess I will have to give up my connector idea, and just solder it back to the board directly, as it was original, after allLuckily it was working fine before, it's only this dim trace problem that bugged me, though was not a shot stopper. I looked at the schematics and I think I do stand a chance that the problem actually comes from the main board rather than the daughter board... we shall see... well assuming I can figure out where the problem lies of course, no guarantee, I am no magician !And then there is still the collet problem, without this tiny little thing, the scope will be missing the time base knob altogether !Yeah, this scope is definitely a test bed... hardly stellar specs, never going to be my main scope, but boy it has so many problems that I learn a lot from it ! At least from this point of view, it's a success !

author: tautech
author_rank: Super Contributor
timestamp: August 17, 2018, 10:42:00 pm
content: Forgot to ask Dubbie when he was here last weekend how the collet project for you was going but he'll see these replies and chime in if he's not to busy with his little'uns.

author: Vince
author_rank: Super Contributor
timestamp: August 17, 2018, 11:01:24 pm
content: Yeah... don't "pressure" him....This collet is yet another example of a small part that I thought could be bought off the shelf but is instead ruining a repair attempt.I enjoy the troubleshooting part, but being stuck because of some stupid little mechanical part, connector or collet or what have you.. it just drives me completely nuts, I have to admit....

author: Per Hansson
author_rank: Unknown
timestamp: August 23, 2018, 09:49:08 am
content: Hi Vince, spent a couple days reading this magnificent writeup of yours, it's really a nice story!As for the pinstrip why don't you just cut it into individual pins? You could then just solder them one by one.Or put them on the delayed time base board (one by one) and link them together with some super glue.Could even make a small "jig" so that you will get the correct dimension, looking like new that wayAs for the collet, do you have exact dimensions of it? If so please PM me and I'll see what I can findIt's my thank to you for this excellent writeup, I have a 2215 too that I will now mod the transformer in.According to the PDF you posted about further back:SUP3010M50226

author: Vince
author_rank: Super Contributor
timestamp: August 23, 2018, 11:27:53 am
content: Hi Per,Thanks for the kind words, and glad my topic is helping you a little bit with your own 2215 !QuoteYeah, I did think of that, as a last resort... but sadly the pins are way too big to fit into 0.1" contacts, it's like giving the Yeti shoes from a 5 year old... it's never gonna do it !...I guess I could also replace the pins on the board one by one, by matching 0.1" pins, right angle... talk about a job ! Also, they would have to be extra-long pins, otherwise they won't clear the edge of the board.. not sure this kind of header is readily available, would have to check.QuoteDo you have some collets in stock ? Problem is they seems to all have different shapes and sizes, they are custom for every Tek scope or pretty muchStill, doesn't hurt to have a look at your stock. I created a thread about this collet, a couple months back, you can read all about it there :https://www.eevblog.com/forum/repair/searching-for-a-18-collet-to-repair-a-tek-sweep-knob/I put a drawing of the collet with pictures.Dubbie and Tautech are kindly teaming up to try to make one, at the other end of the world in New Zealand. Let's see how it turns out (no pun intended)... will it be doable... will it be a nightmare of a job and we must give up... I don't know just yet...

author: Per Hansson
author_rank: Unknown
timestamp: August 23, 2018, 02:35:25 pm
content: No collets in stock but I work for a company that sells & services lathes and millsBut it seems you have come quite far already, I read the thread you linkedAs for the pins some can be bought without the strip too, but need some measurements then.I.e. something like this:https://www.elfa.se/en/dil-socket-tec-pin-003-95/p/14817813

author: Per Hansson
author_rank: Unknown
timestamp: August 24, 2018, 06:26:26 pm
content: I'm curious about the Rifa death caps though Vince, did you not replace yours? I have ordered them too, same partno was still available at Elfa LOL

author: Vince
author_rank: Super Contributor
timestamp: August 24, 2018, 07:52:35 pm
content: Quote from: Per Hansson on August 24, 2018, 06:26:26 pmWell... have to say I don't know what you mean by "Rifa" cap, never heard that term before.OK let me Google it... Oh OK, I see... that's the name of the manufacturer for these squarish semi-transparent yellowish mains rated caps I see in many products.... didn't know they had a nick name !No I didn't replace them since they clearly were not the issue, and didn't show any visible sign of damage.Also, I thought these mains caps were precisely super ultra reliable, precisely because there meant to be used on the mains, so I assumed I should never have to worry about these type of caps.Well that was what I used to think up until very recently... but I watch lots of repair videos from various people, and it appears these caps can indeed go bad in old device, to my surprise ! And actually, no later than later last night/early this morning, I was watching a repair video from a channel I am subscribed to : "Artifact Electronics". The guy was repairing an old TRS-80 8 bit computer, and during this very repair, a "Rifa" cap in the SMPS released the magic smoke !!!https://youtu.be/gVtp0YuLP94?t=731So yeah, at least now I know this type of cap can fail...

author: tautech
author_rank: Super Contributor
timestamp: August 24, 2018, 08:14:03 pm
content: Rifa's are used in the incoming mains filter X-Y network, they are an old brand name and the other common one to fail is Schaffner filters. Either create a bit of smoke, stink and sometimes a blown fuse and if you're unlucky some localized damage. For a bit, equipment is perfectly capable of running without mains input filters although their usage also manages SMPS noise being emitted onto the mains.

author: Vince
author_rank: Super Contributor
timestamp: August 24, 2018, 08:47:26 pm
content: Shaffner ! Ah yes, this one rings a bell, I learned about it just a few days ago ! Someone on Tekscope ISTR, having problem with a 2215 SMPS again, IIRC !I need to do some reading on X Y caps... am gathering bits of info here and there on YT as I watch more and more repair videos.Well simply knowing they are called X and Y caps is already something !Then if I am not mistaken, the letter X or Y refers to how they are wired on the mains. "X" means the cap is straight across the live and neutral wires, so if this one goes bad it can of course short the mains ! Scary...Then the ' Y ' caps always come a pair : a common point tied to the earth wire, then one cap goes to neutral and the other to live.So there are two use cases, I guess each with its own set of design criteria, so the physical presentation of X and Y caps is different.So this Rifa, squarish caps for ' X ' use, or other squarish looking molded film cap.As for ' Y ' usage, from what I gather, they are usually disc ceramic caps. Either the old fashioned "brown" disc caps, in very old equipment, or on more recent gear, a thick, blue coloured disc.That's about all I know for now. What I need to figure out among other stuff, is I see sometimes a digit appended to the letter : X1, X2, Y1, Y2.. something like that. I need to figure out what that means...

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 25, 2018, 09:48:48 am
content: I own this scope and it's my 1st analog scope. Sometimes I think it has issues, but I don't really know for sure, I need more experience.How complicated to work on, is this era of scopes compared to ones full of processors in the 80s ? I love the older stuff, it's so much more "hands on" so to speak

author: james_s
author_rank: Super Contributor
timestamp: August 25, 2018, 03:33:51 pm
content: I just worked on a 2215A the other day, they're incredibly simple compared to most scopes I've been inside. I was actually surprised at just how little is in it.

author: particleman
author_rank: Regular Contributor
timestamp: August 25, 2018, 04:13:59 pm
content: The 2215 is essentially one big board compared to a 4 series scope which are a cube of boards around more boards. On the 2215 just slide out the CRT and remove the attenuator/sweep board and you have full access to everything.

author: james_s
author_rank: Super Contributor
timestamp: August 25, 2018, 06:21:22 pm
content: One warning I can give about the 2215A, don't wash the V/div knobs in an ultrasonic cleaner! I did that because they were totally gross and indeed they came out squeaky clean. So clean that there's no trace of the printing that was on the transparent portion! So if anyone has a pair of those knobs for a modest price let me know. Alternately a good scan I could print on transparent waterslide would probably work. The scope is far from pristine and has some other issues so it's not worth investing a lot but it's a Tek so I can't bring myself to junk it.

author: Vince
author_rank: Super Contributor
timestamp: August 25, 2018, 06:44:14 pm
content: Quote from: james_s on August 25, 2018, 06:21:22 pm"Luckily" I don't have the luxury of an US cleaner, so just good old detergent and brush for me, works fine. Thanks for the warning though, as I sure intend at some point, to get an US cleaner...QuoteI feel for you. I need to buy some broken knobs for my 2232. Looked at Sphere and Qservice, the main suppliers.... lessons learned : knobs on these scopes cost a fortune, assuming they are even available at all. IIRC the Volts/dic knobs were available on Sphere, for an insane amount of money, the you double it to import it to Europe in my case. If you are in the US at least you get cheap shipping so it's not so bad.As for scope smiplicity, this 2215 is simple but somehow I find the more modern CRO TDS scopes, much simpler and easier to work on. My TDS 544A was a joy to work on, with two large board where everything is there accessible, for you to probe at will, while the scope is running.The award goes to my TDS 310 (or any TDS 300, all the same) : there is just one tiny main board the size of your palm, which contains everything, and then just the front panel board which can be popped out easily and again, be probed at will while the scope is running. A joy. Only problem with the SMPS which is quite complex and third party so no schematics available, never mind a service manual. I have to repair one and it's not fun.. still not diagnosed. Might come back to it one day...QuoteYeah same here.. mine is in good nick overall, but not worth investing money in it... but as you said it's a Tek, not some no-name crappy hobbyist level scope that flooded the market in the 80's an '90's... so I do what I reasonably can to sort it out...

author: Vince
author_rank: Super Contributor
timestamp: August 25, 2018, 06:56:46 pm
content: Quote from: lordvader88 on August 25, 2018, 09:48:48 amJust start a topic of your own so we can help you out more efficiently... otherwise this thread will become confusing and unmanageable.Post a link here to your thread once you have created it, will see you there...QuoteWell actually the 22XX scopes ARE from the '80's... so not sure what you mean ;-)The ones with processors are for example the 2232 because it's both analog and digital at the same time. There is a processor board that handles the digital/storage stuff, but it's a standalone board. The scope is otherwise a "normal" analog scope like this 2215 scope or friends. So you don't have to actually worry about the "processor stuff"... you can just treat them as a regular 22XX scope. Once the analog part of the scope is working, you can work on the processor board if need be, but only if need be. A dead processor will not keep the scope from working as a regular analog scope. It's a very modular/fail safe design, I like that...If you have in mind the more complex analog scopes of the day, the 2445/2465/2467 etc, then yeah they are much more complex and are designed from the ground up around a processor. So if anything is wrong with the digital part of the scope, you are in trouble. They definitely are not the best choice to hone your repair skills. The old 22XX scopes are indeed a much better choice. All discrete components, readily available for the most part, great service manual, low component density/easy to probe... it's definitely a good place to start, I think ! It will give you a good understanding of how a scope works, and train your brain for trouble-shooting. Then you can move up to more complex scopes, with surface mounts stuff, higher density and more digital stuff, if you wish.QuoteYeah

author: Per Hansson
author_rank: Unknown
timestamp: September 14, 2018, 09:33:25 pm
content: Quote from: Vince on July 03, 2018, 09:27:35 pmHave you looked at the gate waveform after this change? (Tektronix measure point 25 in the schematic)Here are three different examples I tried on my A18 board with a 1A load, as you can see there is a quite nasty dip in the miller plateau.I suspect it is because the newer MOSFETs have much higher capacitance, so C921 needs to be scaled up.Either that or add some resistor on the gate, so it does not pull down the PWM output so much.

author: Vince
author_rank: Super Contributor
timestamp: September 14, 2018, 11:06:13 pm
content: Quote from: Per Hansson on September 14, 2018, 09:33:25 pmNope. Looked at it briefly as I was trouble-shooting the SMPS initially, but haven't looked at it again once I had replaced the FET with something else.It just worked and did not overheat so I moved on to the other problems that need to be addressed.... which are much more complex than the SMPS.This auto-brightness feature in the 2215 is just driving me completely nuts, I am pulling my hair out, losing appetite, losing faith in the ancient Greek God " Elektron ". Spent whole day last Saturday, working/probing the scope... so I made some progress, but still far from a diagnosis... maybe because this scope is acting so erratically that I am still in the process of figuring out WHAT exactly are the true symptoms.... trying to make sense of its weird behavior, trying to see the "signal" in all that "noise" of symptoms.... is not yet fully achieved I am afraid.I am not giving up just yet, but I think I will not spend too much time on it (other stuff on my plate), because I had a look at the service manual for the 2215A scope, the revised/improved version of this 2215 scope... and came to realize that the only thing they changed on it, spec/feature wise.... the only user visible change they made... was to DROP this auto-intensity "wizardry" altogether ! They didn't even try to fix it, they just gave up completely on it, to the trash !So I think if Tek themselves gave up on it.. it must be really, really hopeless, and I am basically wasting my time trying to get to work, something that most likely never worked properly even when new back in the day !So I will not be losing sleep over this 2215...I am not out of leads/ideas just yet, and I hate being defeated, so I am still working it for now... but I also know that it will probably never "just work", so I won't try to make it perfect. Just trying to get rid of the most blatant/inexcusable problems with it, as I am hoping that at least these bits I have a decently reasonable chance of fixing. But I will not spend 10 years trying to iron out every tiny little quirk, because they probably existed even when it was brand spanking new !QuoteThanks for sharing your experiments.QuoteDon't know what is meant by "Miller Plateau", will need to read up on that.I do see however the dip, in the middle of the leading edge, getting deeper and deeper as we compare the successive graphs...is that really of concern ?

author: tautech
author_rank: Super Contributor
timestamp: September 14, 2018, 11:31:37 pm
content: Yes, it is !It can possibly lead to the MOSFET gate drive dipping below levels needed to maintain an ON condition.See the screenshots and the leading edge dip.

author: Per Hansson
author_rank: Unknown
timestamp: September 15, 2018, 09:38:43 am
content: Yes it is a big concern Vince, as tautech said if the dip is too big the MOSFET will turn off! EEVblog video #1119 describes this really well!The graphs in my previous post are comparing different MOSFET's, the type of the MOSFET is the filename of the picture.So the first one is IRF820PBF, that is like the original MOSFET (I have replaced it with a new one though) and even that has a dip down to around 7.5v.That's not great but the point it will turn off is from the datasheet: VGS(th) min: 2.0v max: 4.0v, so we are "ok"The second graph's MOSFET is a IRFBC30, this is actually quite close to what Tektronix changed to in 050-2242-03 asflobydust wrote here.The dip for this goes right down into the VGS(th) range, so it's not good.What's interesting is that there is a change for the 2235 in one of it's later service manuals.At the last pages they add component R909, a 39Ω resistor at the gate of the MOSFET.Of course that will reduce the inrush into the gate and thus the dip will be much smaller.Maybe even gone if the problem is with capacitance as I suspect.The last graph is of the really low RDS(on) part STP15NK50ZFP that I bought, which was a fully insulated part.It also has some nice features like built in zener diode protection from too high voltages between gate and source.However it's capacitance is much higher than the original part, and it's gate dip is really pronounced all the way down to 2v!C921 which I mentioned before sits on the TL494's PWM output, it's an AVX SA205E104MAA general purpose Z5A ceramic capacitor.It has pretty horrible specifications, significantly dropping in capacitance with increased heat or lower DC bias, or AC component.That said it's parallel with the 100µF electrolytic cap C913 so it might not be an issue at all.The one installed on my scope is original, and it measures exactly 0.1µF (103nF) so it's still ok after 35 years.I noticed it's not even present in the 2215's big brother 2235 schematic, so I took it out: there was a bit more ripple, but the dip was exactly the same.So it has no effect at all, I even put another small electrolytic cap parallel above it but it did not make any discernible difference either.Finally I tested to add the 39Ω gate resistor R909 right now, it improved the situation with the original MOSFET IRF820PBF quite dramatically.I have attached a scope shot of that here, and also a picture showing where I installed the resistor.As I understand it the 2235 also has a ferrite bead on the MOSFET, so I'll go see if I can find any pictures of that.The eagle eyed might also notice I've replaced resistor R911 & zener VR917, mine read 161k & 6.0v respectively, so it felt best to replace them since they are 5% components.

author: Vince
author_rank: Super Contributor
timestamp: September 15, 2018, 11:49:46 am
content: Thanks for sharing your experiment son the FET Per, much appreciated because I don't have time nor the inclination to do all that right now... need to move on to the other stuff, can't afford to work on the SMPS for weeks or month on end at the moment...Call me stupid but I don't understand why it is so bad for the FET to turn off during the rising edge, then turn on back on again to eventually become turned on for good. I understand (from your best/worse graph comparison) that it about doubles the turn-on time, so twice as much energy/power to dissipate, hence much more losses/heating up issues... but in the 1191 EEVBlog video they just focus on the very fact of turning-off being bad... but don't say why it's bad. This imply that if, say, the dip was big but the FET didn't turn-off, then they would not care as much about it (other than the increased losses of course).Does this quick on/off cycle "stress" the FET and reduces its life expectancy ? Its whole purpose is to turn off and on all of its life in the first place...Or is it that it would "upset" the "balance" of the control loop/operation of the SMPS. It would also I guess generate more "crap"/noise at the output, but the slew rate of the "second" rising edge, following the dip, is exactly the same as the first one, no faster, so the harmonic content would be the same, hence the existing filtering downstream, would be just as efficient at getting rid of it. Not saying that as an "excuse", but just saying it would probably be not "deadly"...I want to understand betterThe video though gave an interesting bit of info as to why this dip even exists : the Miller capacitance that suddenly comes into play at some point as the gate voltage increases past some threshold, and causes extra capacitance to be "seen" from the gate, hence suddenly putting extra load on the gate driver circuitry, understandably resulting in a voltage drop at the gate.Anyhow. You got me curious Per (and slightly anxious as well ;-) so I will have a quick look at the gate on my 2215, out of curiosity... and also just in case I see a horrible dip. If so , will try adding that 39 ohm resistor in series with the gate. Your experiment about this sounds very promising indeed ! I notice that in my 2232, this 39 ohms resistor comes as standard.In my service manual for the 2215, I see that the waveform they give for the gate (without the 39ohms resistor then), displays no dip whatsoever, bit strange then...Will go have a quick probe for that and report in a bit...

author: Vince
author_rank: Super Contributor
timestamp: September 15, 2018, 08:47:50 pm
content: Here are the results !See pics below. Sorry for them being blurry... was not in the most comfortable of positions : holding the probe in one hand, it hovering scarily close to the 400V cap terminals (had the board upside down, in its normal position, properly secured), and holding the camera in the other hand, trying to press the shutter while making a desperate attempt at remaining steady...Anyway. When you look at the general/complete gate waveform, it looks very much like what's pictured in the service manual, i.e. with a good bit of overshoot and less of an undershoot. Even from this "distance" though, one can "guess"/suspect there is something going on inside the leading edge, as its upper half looks fatter than its bottom half.... begging to zoom on it. And there you go, a big dip like Per showed.The dip is about 50% of the pulse height. It dives down to about 7V, which is twice the typical gate turn-on voltage specified in the datasheet (attached) : I am using a IPP60R280P7 , turn on is given for 3,5V typical, and max is 4,0V. 3.0V Min. So looks like I am well in the comfort zone from this regard.Still, was quite a big dip, so I tried adding the 39 ohms resistor, hoping it would improve things a lot, like it did with Per.... but as you can see it was very counter productive to say the least ! It made things worse, not better. And much worse at that : the dip now gets down to about 3Voilts, 3,5V at best. So, pretty much half the gate voltage I had before, hardly an improvement. And of course, it's now bang on on the turn-on voltage....Concurrently (consequently ? ), the SMPS starting to emit the dreaded whine, argh !!!Removed the resistor, whine was gone and the dip back up to 7Volts, phew !So that was an interesting experiment indeed, you can never make too many experiments eh ?!So this gate resistor definitely makes a difference, good or bad apparently depends on what particular FET it is associated with...... and a possible link to the famous whine as well... so that's yet another lead for when I get round to diving again in the SMPS of my whining 2232 : look at that gate voltage, check if removing removing its gate resistor (mounted as standard on the 2232) helps or not, both with the dip and the whine...Anyway, that was a cool Saturday evening experiment

author: tautech
author_rank: Super Contributor
timestamp: September 15, 2018, 10:48:58 pm
content: It's all about managing the gate drive current draw so to not exhaust the available gate drive with a fast gate rise time. 39 ohms might be too high resistance so down closer to 10 ohms might be a better choice.Experimentation would be required.My mentor recommends 2-5 ohms for gate resistors.

author: Vince
author_rank: Super Contributor
timestamp: September 15, 2018, 11:33:42 pm
content: Yeah would be nice to experiment with different values of gate resistance to see what that does. I do need to build myself a little decade box, indeed.... yet another project ! ...Will try and do that when I get my head again into my 2232 SMPS for its due recapping.But for now I have a new more pressing " project " : yesterday I was tasked with saving the life of an old dishwasher !But it's a professional bit of kit so the electronics inside is interesting, decent quality. It looks like its most definitely an electronics related issue, so they thought of me for having a look at it... hell maybe I could open a new topic for that !Was built in 2005, they bought it used 10 years later for 2,000 Euros (2500 USD), worked for a year just fine, then one day out of the blue, it just decided not to turn on anymore. Front panel is totally unresponsive and all it does is light solid, all the decimal points from the two 3 digit LED 7 segment displays.They got the manufacturer (" HOBART ", American), service Tech to come have a look... said it was the main board... which cost 1500 Euros (1800 USD or so) to replace ! They declined the offer ...That was nearly 2 years ago and has been sitting there unused ever since...Front panel only carries buttons and LED displays and indicators, and has its own 8 bit micro (a PIC 16FXXX something). A 10 wire cable connects it to the main board that's in the underside of the dishwasher... half through hole, half SMD. Good 'ol through hole EPROM for the Firmware, micro don't know what it is haven't looked yet. A dozen relays and provision on the PCB for 8 more ! That's one hell of a dishwasher ! LOLBrought the two boards and interconnecting cable home so I can study them at ease in the lab. I am hoping/thinking it could just be the (much more simple) front panel board that's toast. I mean, even if the main board was dead, say, the front panel being (somewhat at least) autonomous thanks to having its own micro, should at least have SOME life left in it, no matter what the condition of the main board ! Even if it failed to communicate with the main board, I would still expect it to have a "rational" behavior, and still have a degree of responsiveness.So I need to work on this thing right now, unlike my personal projects, I can't afford to let this one rot on my bench for a year, scattered all over the benchWill try contacting the mother ship in the US to ask for a service manual or at least schematics. Not holding my breath though ! Usually these expensive professional gear require you to pay the manufacturer a lot of dosh to get access to their service information. My only hope is that the bugger being not so new, from 2005, 13 year old already, they may be more a little more relaxed about it... will see....Will get back to my scopes ASAP...

author: tautech
author_rank: Super Contributor
timestamp: September 16, 2018, 09:00:48 am
content: Quote from: Vince on September 14, 2018, 11:06:13 pmDunno if this is related Vince, but from another thread:Quote from: drussell on September 14, 2018, 11:15:12 pmFollow the quote to the SUP3010 link.

author: Per Hansson
author_rank: Unknown
timestamp: September 16, 2018, 10:17:44 am
content: Quote from: Vince on September 15, 2018, 08:47:50 pmYour post made me redo my tests, the 2235 manual change that adds the gate resistor does it in a point ahead of the point they use to measure the gate voltage.I looked in the 2215A manual, also attached a screenshot of it and it's the same: gate voltage measure point is before the resistor.Now if I measure after the resistor, right on the gate as I assume you did Vince I see the same thing as you!So what where Tektronix trying to convey here, can someone please explain? (Surely the measure point should be on the gate?)Quote from: tautech on September 15, 2018, 10:48:58 pmQuote from: Vince on September 15, 2018, 11:33:42 pmI did this the easy way: with a multi turn 50ohm potStill using the same IRF820PBF the short version is that the best gate response (measured on the gate) is seen with the lowest resistanceQuote from: tautech on September 16, 2018, 09:00:48 amThis is "only" to make sure the CRT does not burn out from too high filament voltage, it does not affect the auto brightness function.

author: Vince
author_rank: Super Contributor
timestamp: September 16, 2018, 07:58:55 pm
content: Thanks for the extra info.Yes I measured right at the gate pin, because it's the only thing that makes sense to me, and because that's where the 2215 service manual measures it...If they measure it at the resistor end in the 2215 manual, then I am at a loss just like you are... and just to add to the confusion : just looked in my 2232 manual, where the 39 ohm resistor is fitted as standard... they don't even look at the fate anymore, they only give a waveform probe straight at the open collector output of the PWM chip.My only hypothesis is this : they don't care about the dip.. this is their engineering problem to deal with, it should not be a matter to be addressed by a service tech. Plus, the waveform they give, doesn't show the dip, it's not zoomed in enough for that. Also, they hardly mention it in the "Theory of Operation " pages.So, what I think it that their only intention with this waveform, is to show us thee PWM output in general, and show us that some overshoot is acceptable/normal.So, it does not really matter where exactly they probe for the PWM signal.. it will always look the same : still the same voltage levels, still the same square signal, still the same duty cycle, still the same overshoot.The fact that the probe it a different points, depending on the scope model, maybe simply because mostly likely, the measurements / manuals where made by different people. Their only intention was to document the PWM waveform "in general", so different people probed at different locations, depending on their mood or personal view on where was the best place to probe.I don't think there is much more to it than this...Now about the dip, the manual clearly did not mean to address the issue at all... it's only US who decided to look for this thing...so nobody but us can decide where its best to probe for it. Obviously probing right at the gate pin on the FET package, is the only way that seems relevant.. since the FET reacts based on whatever it sees on its gate.. it doesn't care about what the signal looks like elsewhere...My view on all this any way !

author: tautech
author_rank: Super Contributor
timestamp: September 16, 2018, 08:03:04 pm
content: Quote from: Per Hansson on September 16, 2018, 10:17:44 amTek would've not wanted the added confusion of observing the miller dip on the gate, they only needed to show an 'expected' gate drive waveform.As this recent discussion displays, choice of a low gate capacitance MOSFET is important if the gate drive available is not strong.Another comment offered by my mentor; hammer gates with sufficient drive !It's very plain to see why he made this statement.Could Tek have added a dedicated gate driver, yes but at increased cost.Careful choice of components is the alternative.

author: Vince
author_rank: Super Contributor
timestamp: September 16, 2018, 08:40:15 pm
content: Quote from: tautech on September 16, 2018, 08:03:04 pmThat's two of us thinking that then.. Per are you joining the band and call it a day ?!QuoteYeah sounds good, though IIRC from the Art of Electronics (?), one also needs to be careful with that, it's not impossible to make the FET/ gate oscillate, and one reason why putting a small resistor in series with the gate is always a good idea, to dampen things and keeps them from going completely haywire.Now I read that book 21 years ago so my memory might be corrupted by now.. will have to dig out the book and read it again...You keep referring to your mentor, this is all very mysterious, I am getting intrigued... who exactly was your mentor ?....QuoteHardly an expert, but the scope is from 1981 or something, so designed in the late '70's, power FETs were in their infancy or almost, I assume.. so chances are there did not even exist dedicated gate driver chips back in that day, to begin with ?! .... or maybe too experimental and/or expensive, so Tek preferred logically to roll their own driver with this discrete transistor...

author: tautech
author_rank: Super Contributor
timestamp: September 16, 2018, 09:11:09 pm
content: Quote from: Vince on September 16, 2018, 08:40:15 pmCareful selection of components available at the time is the key to understanding what and why they were used.Tek engineers did the very best with what they had to work with.....at the time.Yes today, it would be done differently.My mentor.....a good friend and Dr of EE and wizard at maths.......I am not !

author: Per Hansson
author_rank: Unknown
timestamp: September 17, 2018, 06:00:48 am
content: Quote from: Vince on September 16, 2018, 07:58:55 pmThat's not what my 2215 service manual says, see attached screenshot.It measures the gate signal on the pin of CR931, one theory I have is that they made it like that to reduce the risk of a probe shorting gate to source, with resulting critical damage.Quote from: Vince on September 16, 2018, 08:40:15 pmWell, as I mentioned I have replaced my IRF820 with a newly produced part, I'm not sure it's exactly the same as what was there originally, this is what I used: Elfa artno171-15-223, a IRF820PBF MOSFET.Basically I'm trying to make sure I'm not changing the circuit too much, the lower RDS(on) part I bought: STP15NK50ZFP, that I feel deviates too much from my tests on the previous page. (Likewise for the scavenged IRFBC30).I also have a theory about the added 39Ω gate resistor R909: that it acts as protection if the MOSFET fails, when my original IRF820 failed it did not take out any other components.Interestingly it has 42Ω resistance between gate and drain and 13Ω between gate and source now that it's failed...

author: Vince
author_rank: Super Contributor
timestamp: September 17, 2018, 11:33:27 am
content: Quote from: Per Hansson on September 17, 2018, 06:00:48 amThe MOSFET failed in my 2232 and boy that 39ohms resistor sure didn't do much for protection : mains voltage got in there, blew the gate driver and the entire PWM circuitry behind it, PWM chip literally exploded, was not a pretty sight in there...

author: Per Hansson
author_rank: Unknown
timestamp: September 17, 2018, 07:43:08 pm
content: That's a good point of reference VinceI just readTK5Q65W_application_note_en_20180726.pdf, it made my head hurt a bitI understand the purpose of the gate resistor a bit better after reading that.Still from the tests we have shown we just get a worse response for the turn-on.I mentioned some tests I did with C921 earlier, and found no big difference.But should the issue not lie there, i.e. C921 is unable to provide the necessary gate drive?

author: Per Hansson
author_rank: Unknown
timestamp: September 28, 2018, 09:48:08 pm
content: Did some more tests today.Used the final MOSFET I had bought for this project, a IRF840LCPBFOut of the low RDS(on) MOSFET's this had the best gate drive characteristics.I then scavenged a 35v 10µF Epcos tantalum capacitor and added it in parallel with C921: no real difference.But before calling this project quits I want to ask one question:Pin 13 on TL494 is tied to ground so both outputs are running in parallel, I have verified this with my scope.But only pin 10 (the secondary output) is connected to the MOSFET.Pin 9 (the primary output) is not connected to anything.If I wired them together would I not get twice the gate drive capability?If the answer is yes then why did Tek decide to not do it?I want to ask before I try and blow up my power supply...

author: Vince
author_rank: Super Contributor
timestamp: September 28, 2018, 10:24:37 pm
content: Yeah good question !If I understand the datasheet correctly, there is there two selectable mode of operation with regards tot he tow output transistors :- " Single-ended " where they turn on and off at the same, time, and can therefore be paralleled for extra current.- " Push-pull " where the two transistors are driven in a mutually exclusive way. When one is conducting, the other one is open.I guess that since Tek rolled their own gate driver, that there was no need to parallel the two outputs from the PWM chip, as one was already more than enough to drive the external gate driver. If they wanted more current they would have probably modified their own driver rather than paralleling the two outputs ?!Also, the specs of the output trannies were maybe deemed not fit enough of to achieve the gate driver specs they wanted, other wise they would have not rolled their own driver in the first place, I guess ?Point is... Tek engineers aren't there to tell us, so let's not torture ourselves with questions that just can't be answered (just guessed at, at best)...

author: Per Hansson
author_rank: Unknown
timestamp: September 29, 2018, 07:33:27 am
content: Quote from: Vince on September 28, 2018, 10:24:37 pmThere is no external gate drive Vince, the TL494 drives the MOSFET directly.The only purpose of Q931 that sits on the gate is to discharge the gate quicker than what R931 the 3K resistor would do on it's own.The TL494 can supply 200mA on each of it's transistor outputs.Curiosity killed the cat and I had to try it: I wired the two outputs together (shorting pin 9 & 10 together).The result in attached screenshot, it's almost as good now as with the original MOSFET so I'm very happy with that!

author: Vince
author_rank: Super Contributor
timestamp: September 29, 2018, 08:10:55 am
content: Quote from: Per Hansson on September 29, 2018, 07:33:27 amFirst time anyone points this out in this long discussion, so I am bit surprise !But yes... just looked at the schematics again, and the theory of operation pages... I somehow missed this important point since the beginning !Scary...Still, you would then have to wonder why they rolled their own "gate discharger" (not gate "driver" then, OK ;-), since the 494 as we just said, CAN be configured as a push-pull output precisely to drive the FET AS WELL as discharging it.So back to square one...QuoteYou now are the official 2200 SMPS experimenter !

author: floobydust
author_rank: Super Contributor
timestamp: September 29, 2018, 04:21:55 pm
content: TheTL494/594 output stage is for driving BJT's, so it's always a hassle to drive mosfets with it. I have never used single-ended mode with pin 13 grounded.We'd have to estimate the gate-drive requirement to see if that mode would work or if adding an NPN driver+resistor to the TL494 output is needed for high capacitance mosfets.I tried an LT SPice sim with 2235a circuit but not sure of the transformer winding inductances. With measured in-circuit values, no Miller plateau as large as what is reported, even with 240VAC line, so the sim needs some work. It's not a vanilla flyback converter with C907 at 1uF; I could not find decent mosfet Spice models. IRF840 has a leisurely 0.16Apk gate drive.I measured:T906 1,2 3.50mH 2.05 ohms Primary WindingT906 4,5 3.75mH 1.57 ohms Reset WindingT906 9,10 4.50uH 0.22 ohms Tank WindingT906 6,7 452uH 2.00 ohms Aux WindingFairchild (On-semi) SemiconductorSuperFET Model Librariesare encrypted and did not work for me.ST gives six Spice models per mosfet,User Manuals UM1575: Spice model tutorial for Power MOSFETsBut I could not find Spice models on theirwebsite

author: Per Hansson
author_rank: Unknown
timestamp: September 30, 2018, 06:03:28 pm
content: Well, it's quite difficult to calculate it, at least that was my conclusion after reading up on it.Thus I just tried it instead, gets more useful data that way anywayIn my previous posts I mentioned I used a 1A load, actually it was two 100Ω resistors so totaling 50Ω and a load of 0.86A if my math is correct.If I remember right my load meter showed 43w, which would mean the PSU is 86% efficient at 240VAC.The picture attached to this post is with the reading taken with the scope as load instead of the dummy 1A load...The dip is a bit smaller: the reason is that the scope presents a bit smaller load: meter shows 35w to 36w when I have a trace on the screen...

author: wermundo
author_rank: Newbie
timestamp: December 30, 2018, 06:42:11 pm
content: Hi,i'm not sure if i'm right here, but i currently try to fix my Tek 2215 and so i just found this post.I managed to find that the Q933 and Q931 is defect, for the Q933 it's no problem to find replacement but for the Q931 i can't find anything. The label says TI114 i guess. If i understand it right, it is a Tektronix "own" component? Do you have any suggestions for replacement part? Or is it not even necessary to replace because the TL494 can operate in push-pull mode like i read here (shorting pin 9 and 10 together)?

author: Per Hansson
author_rank: Unknown
timestamp: December 30, 2018, 08:47:17 pm
content: Did you read reply #114 to #116 above?You can't operate the PSU without it, it's purpose is to discharge the gate current.The TL494 is not setup in push/pull operation mode but in parallel operation mode.So you either need a new Q931 or if you want to get fancy you could change the TL494 into push/pull operation mode and use it to discharge the gate current.But since Tektronix did not do this to begin with I would assume they had their reasons for it...The post here talks about a possible replacement for Q931:https://www.edaboard.com/showthread.php?180408-Tektronix-2213-preregulator-fail

author: Chris56000
author_rank: Frequent Contributor
timestamp: February 02, 2020, 03:12:14 pm
content: Hi!Just a courtesy–note for Member Vince to say how much I enjoyed his Tek 2213 writeups – these writeups written clearly and with plenty of pics and circuit diagrams are exactly what less experienced Members need to help with difficult problems!As to Vince's English – as a native UK English speaker myself I cannot fault it – it's as good as any British person who posts on here!Please keep your repair tales up Vince, I enjoyed reading them, so much so I'd like a blown up 2213 myself to try, but they've nearly always been only in the USA, and US sellers' sale prices and postage charges are just getting ridiculous!Chris Williams

author: Vince
author_rank: Super Contributor
timestamp: February 03, 2020, 06:04:39 pm
content: Hi Chris, thanks for the kind words, you have me all red faced now !Sorry for my long absence, I was moving home and it didn't go well at all ! The house builder turned out to be very crooked indeed ! He was supposed to give me the keys in November 2018 but refused to because he didn't want me to notify in writing all the crap work he did here and there....a couple lawyers and over a year later...I finally got the keys no later than last Wednesday ! So your message is incredibly timely !I have started today doing the final work inside the house that's required to be completed before I can move in : sand down all dry wall all around the house, including the ceiling (a pain in the butt to do !), then I will be able to paint the house, and move in at long last !I have never done this kind of work before so I expect it to take some time, as I learn as I go...But I am hoping it could be done in couple weeks, then some time to put the lab all back together again....and hopefully in a month max from now, I should be back in business fixing my old Tek scopes, and therefore posting here again about it !While I was off-line, I had the opportunity of buying quite a few nice old "classic"/ tube Tek scopes...I just love these things, can't help but buy all those that are within reach fuel cost wise ! :-)So stay tuned !

author: BiasedAmpere
author_rank: Newbie
timestamp: February 06, 2020, 05:37:35 am
content: >using TapatalkWhat other forums do you use also?

author: Vince
author_rank: Super Contributor
timestamp: February 06, 2020, 11:29:32 am
content: I use the "Tekscope" forum for Tek scopes specific stuff, since I have many of them, but that's about it.The EEVBlog forum is my main playground for electronic stuff.