Dead Tektronix 2235 - Page 1
Forum section: electronics / repair

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: September 25, 2020, 08:46:33 pm
content: Hey guys, first post here... I left my Tek 2235 powered up overnight accidentally a few days ago only to find it dead the next day. No power LED, no smoke, no funny smells, no sounds, no nothing. Luckily it didn't decide to catch fire or something and burn the house down! I know the PSU is the likely culprit here as most of these have been gone through already but mine looks to be 100% factory stock. I just made the digi-key parts order under NFM's (excellent) video on the popular video channel. Hopefully a full recap as well as the 050-2242-03 service bulletin upgrades will bring it back to life. Stay tuned...

author: bd139
author_rank: Super Contributor
timestamp: September 25, 2020, 08:49:16 pm
content: Some notes here which may be of assistance. Good luckhttps://www.eevblog.com/forum/testgear/tektronix-2235-repair-thread/

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: September 27, 2020, 05:24:39 am
content: Thanks bd139, yeah, I saw your thread earlier while doing some poking around in here... it looks helpful for sure.I just pulled all of the 840uF mains caps and C906- the big 75uF can - as well as C940 which I think was replaced at some point. It was a 50V 1000uF nippon chemi-con. Don't want to pull too much out as I generally like to replace as I go and parts aren't here yet.I do think I got the fan area sorted out though - the pad areas on mine are way over right next to the side of the chassis, and comparing to the skit that NFM has up it looks the same. Not too worried about the fan yet though since it won't even power up yet! Ha!

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 01, 2020, 06:01:42 am
content: So far I replaced all of the PSU caps (I think). My attempt at taking NFM's digi-key parts list and cross referencing it to corresponding schematic parts as well as what I've done so far below:1) 120uF 450V radial - C906 - replaced1) 33uF 200V radial - C954 - replaced2) 2.2uF 50V radial tantalum - not replaced yet but I'm pretty sure these go on the attenuator board2) 1.0uF 50 axial - ?3) 2200pF 1kV radial - C902, C903, C904 - replaced3) 2.2 uF 100V axial - C90, C91, ?1) 0.15uF 1kV radial film, C900 - replaced2) 10uF 160V radial - C942, C943 - replaced4) 3.3uF 50V axial - ?1) 1uF 100V radial - C944? I see it on the skit and the screenprint on the back of the board but it doesn't seem to exist on the front of the board? It should be on pg 162 of the service manual and I don't see it there either?7) 1000uF 50V radial - C960-963, C968, C970, C940 - replaced1) 100uF 50V radial - C925, replaced (this one sucked ass! - damn chassis in the way!)1) 270uF 63V radial - C956, replaced10) 22uF 50V radial - ? (I see lots of little ones that I haven't gotten to yet)I figured I'd plug it in and see what's up. Nothing but "tick tick....... tick tick..... tick tick....." I don't think I even got that before but maybe I did, I dunno. I didn't have the case off like I do now.I haven't done the service bulletin mods yet. That's next. Gotta get the power supply going again before I screw with anything else!edit 5 minutes later - I see C944 now! Tiny little bastard! I also see three other tiny little axial bastards on the main board... back at it soon...

author: bd139
author_rank: Super Contributor
timestamp: October 01, 2020, 08:08:24 am
content: Good luck. Power supply start up is the usual pain in these. The supply is in two sections, a preregulator and a secondary SMPS. The secondary SMPS will come up on 43V DC at two test points on the board. Always worth checking with that first. The preregulator is the trouble on these as it likes to explode in your face I find. If I ever get my hands on another one I'm bypassing the entire thing and sticking a 48V MeanWell unit in there instead!

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 02, 2020, 04:47:52 am
content: Thanks bd, I replaced C944 tonight and C200 and C201 while I was at it (two other tiny axial bastards - these are a bitch! I kinda butchered two pads - dammit! - but everything checks out as far as I can tell). Didn't have a whole lot of time. I was really hoping C944 was the culprit as it looks to be critical judging by the schematic. Plugged it in and got the same "click click.... click click...." and no power LED... so NOPE!Next time I work on it I'll dig around in the service manual and look for those test points like you said. If those look ok I'll give the service bulletin PSU upgrades a go...I know what you mean about bypassing - I have a basement recording studio with a Soundcraft Delta 16 channel board from the 80's I think? Great board but the factory PSU is a total joke. I built a little birch 13-ply box housing two Power One units - one for the board and one for 48V mic power. The factory PSU now sits on a shelf where it belongs! But that is an outboard standalone supply, unlike this damn thing...edit - re-reading your thread now for knowledge/inspiration... the back and forth between you and David Hess is so far over my head it's not even funny. I have an engineering degree and own and maintain 1800+ watts worth of vintage tube amps (which is the reason I bought this damn scope!), but fixing this thing might be WAAAAAAAY beyond my dumb ass... I won't give up yet tho! Not yet!

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 02, 2020, 05:16:34 am
content: Sorry to be negative here but why? It’s a simple question. Why?The scope is dead. And you just start replacing caps? Why?Have you measured the power rails? Check the ripple voltage? Anything? It’s all in the service manual. The voltages are easy to measure.I simply don’t understand why people just start ripping what are perfectly fine caps off a board in mass. Get it working first. Check the ripple voltages. That’s when you replace the caps that need replacing, if any. Sure, if there are signs of leakage, they go. If the labels are cracked from heat, they go. But as the first step in a repair process to start ripping parts off a board? That most times creates more problems than it solves.I wish you success but what if it turns out to be a bad hv transformer? Then what do you do with all those new caps?

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 02, 2020, 05:18:15 am
content: Why? 1985. That's why.

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 02, 2020, 06:00:43 am
content: Sorry Watts, not trying to be negative either, but at last count I've got a...:Marantz 2245Marantz 2270Sansui 8080DBDynaco ST-70/PAS-3Scott LK-48BFisher 400B&K 747B tube testerHeathkit IG-18Heathkit cap tester - can't remember the model - the one with the "magic eye"Not to mention all my bass amps (anyone else own three 70's Ampeg SVT's? Hiwatt 200?) and guitar amps that I've fixed which have all done just fine with my method - the shotgun one. If I find an electrolytic older than 20 years, it goes. No questions. I've done well so far.edit - I know I'm new here. Don't want to step on any toes but I think I "kinda" know what I'm doing...

author: bd139
author_rank: Super Contributor
timestamp: October 02, 2020, 06:17:34 am
content: Yep. I’m not normally a cap swapper myself but the 2235 has some really hooky ones in it. You build up a list of “potential targets” in gear after a while and it pays off.As for duff ones I received an HP power supply yesterday with a really top end Sprague 32D compulytic which was open circuit. Dated 1989. This does happenTesting isn’t even conclusive. I’ve had ones that report good on my ESR meter and my LCR meter and piss out their electrolyte almost immediately.

author: floobydust
author_rank: Super Contributor
timestamp: October 02, 2020, 06:22:50 am
content: I use this 2235/2235A PSU electrolytic capacitor list, and replace them without troubleshooting down to the component level. That is a waste of time when you know the old Spragues have dried up and Sangamo's cracked and pissed. So far, I always find low value or leaky or open caps in 2235's.Some were upsized for the 2235A so I do that in 2235's - the 840uF to 1,000uF.

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 02, 2020, 06:34:14 am
content: Oooooh - flooby - I see your list - thanks! I will save it.bd I've had ones that test good as well on my Heathkit dude and do not pass the mustard in-circuit. So maybe I'm not nuts to shotgun... Let's see if we can get this damn thing working! Back in a day or so...

author: BravoV
author_rank: Super Contributor
timestamp: October 02, 2020, 06:53:04 am
content: Quote from: floobydust on October 02, 2020, 06:22:50 amWow thank you, sorry abit off topic, especially to bd139, as with my recent acquisition of "dead" 2215, this list should be handy right ?

author: beanhauler
author_rank: Contributor
timestamp: October 11, 2020, 01:42:37 am
content: For anyone trying to fault find this scope i think the procedure listed for the military version is probably the best plan.Lift up the resistor on the emitter of the two push pull transistors R949 listed a 1 ohm.put the scope on a variac if you have one and slowly wind the ac up to about 80v monitoring the voltage between 950 and 940.If it comes up to 43V then the pre reg is fine, If no 43V then the pre reg is the issue.if you have 43V now start looking around the power transformer.In its click click overcurrent state there is no point checking around the pre reg as the voltages are constantly being set and reset by the overcurrent sense around the 0.2 ohm resistor which resets the pre reg chip.Check all the diodes on the o/ps and measure the resistance as follows:-8.6 TP500 114 OHMS+8.6 95 OHMS AT W975+5 330 OHMS AT W 985+30 905 OHMS AT W965+100 12.5K OHMS AT W966IF YOU FIND ANY REALLY LOW THEN CHECK THE CAPS BY LIFTING ONE LEG.STILL LOW THEN INVESTIGATE FURTHER BY LIFTING THE LINK OR LINKS IN THE CIRCUIT CONCERNED.If that fails you may have a shorted turn in the transformer or a cracked ferrite former.Only way out may then be to look for another transformer.The former on these has 22 pins and a very imperial inch layout so any attempt at a wind with a different former would be difficult at best.The HV wind is 1025 T #39 for a voltage of -2050V and i know someone has attempted it and succeeded but its probably difficult.+30 is 16T #23+100 37T #31+5 3T #24+8.6 and -8.6v 5T #24filament 6.3v 3.5 T #24The main core is also encapsulated with resin so if you just have shorted turns then it would be very difficult to rewind without rewinding it completely i guess and re-encapsulating in a pressure chamber. Otherwise you would probably have corona issues and flashover at 2K plus.I am waiting for another transformer to try as i have a broken ferrite core and have exhausted all the above.I will post the result after i fit it....who knows if it will. I am not sure when i will give up.Actually if it does not fix it then the problem could be the inverter itself or the feedback self oscillating transformer although its very low current and unlikely to break. watch this space.Like the idea of seeing if it will run on a 43v independent supply but you would need to monitor the supply current.It may be that it will run on the 43 with more current if the no of turns has reduced in the primary 20T+20T #25 but the core may then start to saturate due to the reduced number of turns and overheat as the resistance is now moving towards the resistance of the wire itself .20T of #25 looks like 0.2 ohms at a path of 94mm ish which is an instant short .Continuing my quest on the 2235 scope and while waiting for another transformer i decided to tear down the old one.Waded my way through the first two winds on the first layer which has plus and minus 8.6 with 5 turns and wound next to it plus 5v with 3 turns all Bifilar and hit the first layer of heavy duty tape...what is that stuff? about 3 mm thick and ran in to the HV wind. This HV wind actually straddles the pins on the former from pin 8 which is grounded to an exit point at the top of the transformer where the #39 wire is soldered to a HV wire before exiting.On looking at the connection between the very fine wire and the lead out i noticed that around the solder connection it was very black and sooty...is this likely my problem i wonder. If it is i wonder if the multiplier has been affected.....time will tell

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 11, 2020, 12:29:04 pm
content: Quote from: Rickenbackerman on October 02, 2020, 05:18:15 amI totally agree with WattsThat.Some people have developed a real paranoia about electrolytic capacitors, and in the majority of cases this is not justified.Systematically changing all the electrolytic capacitors is a strategic error in the diagnosis and in the troubleshooting, for several reasons:1) there is a risk of introducing new failures: damaged printed circuit tracks, assembly or value errors, new capacitor defective or needing to be reformed, ....2) small variations in ESR or capacitance generally have no influence on most analog circuits3) The life of an electrolytic capacitor is not measured simply in years but in time and temperature of operation.It also depends on how well it is built.To conclude that an electrolytic capacitor needs to be replaced just because it is "old" is a fundamental mistake.I have for example a Marantz 2285B receiver from 1974, all its electrolytic capacitors are the original ones except one and it still has all the original performance.Only those electrolytic capacitors which are visually defective (swollen case, liquid leakage), which are measured as being short circuited or which are known to be generally defective such as certain brands and years, or those which are nearby from a heat source should be systematically replaced.Apart from these exceptions, it is necessary, before any component replacement, to make a precise diagnosis of the failure.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 11, 2020, 12:50:34 pm
content: Quote from: beanhauler on October 11, 2020, 01:42:37 amVery good diagnostic strategy but I prefer to leave the pre-regulator test for later, not to supply the oscilloscope by the mains, but rather to supply C940 directly at 43Vdc with current limitation at 1.5A by an external dc power supply.It is much safer, from all points of view, because we do not work under dangerous mains related voltage.

author: bd139
author_rank: Super Contributor
timestamp: October 11, 2020, 12:53:59 pm
content: Also good for the nerves because the preregulator is a bit explodey

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 11, 2020, 01:20:47 pm
content: Regarding the pre-regulator, I would like to add a point that few know about.I read in another topic that some consider that the 2235 is not running hot because it consumes little.This is indeed the impression we have because the case does not heat up much.However, the problem is that the airflow in the oscilloscope is very poor.On the contrary, some components, especially of the pre-regulator, operate at a high temperature, too high in my opinion.This is particularly the case with the T906 inductor and the Q9070 mosfet.This undoubtedly has a very negative influence on the reliability of the pre-regulator.That is why I strongly recommend installing a fan in your 2235.Everything is planned for this, see the 2236 service manual for the information needed to install a fan.

author: bd139
author_rank: Super Contributor
timestamp: October 11, 2020, 01:23:30 pm
content: I think the main issue with the preregulator is the MOSFET they specified was fairly tight on the SOA. If you swap it for a newer onewith a larger SOA window in this use case (I think I used an IRF820) it's less likely to explode.Oh also in the early ones the MOSFET is attached with a crappy molex connector. That's not going to help.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 11, 2020, 01:41:39 pm
content: Yes, but this is not a major concern because it is easy to repair and we have now MOSFET far better than in the past.Those Molex conectors are mostly almost cooked and it is obvious that the wires must be soldered.But the most severe failure is when inductor T906 is cooked for working at a too high temperature for a long time : you will never find a spare part to replace it.

author: bd139
author_rank: Super Contributor
timestamp: October 11, 2020, 01:47:21 pm
content: Yes indeed. On your last point, the only answer is to buy more than one scope

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 11, 2020, 02:28:15 pm
content: Quote from: bd139 on October 11, 2020, 01:47:21 pmOr to install a fan before this happen !!!!NB: I have installed a fan on my own 2235.

author: floobydust
author_rank: Super Contributor
timestamp: October 11, 2020, 08:03:26 pm
content: No need for a fan at all, even Tektronix concluded that with the 2235's.I like that they are quiet and not sucking in dust through the switches and the PSU has less load - with no fan. My preference.

author: jdragoset
author_rank: Frequent Contributor
timestamp: October 11, 2020, 09:49:36 pm
content: This guy has numerous 2235 "parts mules" that many of power up with EHT.alltest_surplus

author: beanhauler
author_rank: Contributor
timestamp: October 11, 2020, 11:19:07 pm
content: This alltest place is amazing. Shame its in the US as the shipping is so expensive to the UK

author: james_s
author_rank: Super Contributor
timestamp: October 12, 2020, 12:32:13 am
content: Quote from: akimpowerscr on October 11, 2020, 12:29:04 pmAgreed, sometimes there is a good reason to replace the capacitors, but I have seen an increasing amount of equipment that started out with some minor problem before somebody made it far worse by a ham-fisted attempt at replacing all of the capacitors. If it's a 1937 radio full of wax paper capacitors I replace them, although even then I usually replace the any obviously bad stuff, test what I can and then carefully ramp up the voltage to evaluate the state of things, then replace the remaining caps one at a time, testing it again after each one.

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 12, 2020, 05:43:41 am
content: I agree with you guys on the "ham fisted" cap replacement approach, sticking random shit in (sometimes backwards), ruining traces and slinging solder all over the damn place. Seen it and have a serious distaste for it. I assure that my approach is not that way. One at a time, careful cap selection, checking and double checking everything as I go, surgical soldering with nice tools and a magnifying glass and a GOOD light (that is key as you get older, heh).Took a little break from it but just started on the service bulletin upgrades. Haven't seen any obviously fried stuff yet. Once I finish I reckon I'll just hit the switch and pray. I figure either I'll:1) blow something up2) PSU won't power up (as was the case when I started), or3) I'll get a trace and all will be right with the world

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 12, 2020, 08:52:55 am
content: Quote from: floobydust on October 11, 2020, 08:03:26 pmIt's not that simple: the 2236 has a consumption on 43V rail barely higher than the 2235 and Tektronix decided to install a fan on all the 2236.The 2235 is "on the edge".In fact, anything that gets too hot has a quite finite life.Tektronix probably did not predict that 2235 would be used for more than 40 years !!!!Measure the temperature of T906 in operation, cabinet closed and you will understand.

author: m k
author_rank: Super Contributor
timestamp: October 12, 2020, 02:11:59 pm
content: I think the cap swap thingy is a result of few mishaps, or so.One is that the person who was originally doing it right was giving a wrong message.Like a newbie watching a repair man doing high power amp stuff from heavy duty early days.Then later not so newbie anymore sucseeding with that method with something a bit away from ones own area.Pretty much quaranteed one cap swapping agitator more.For newer and small caps you propably need that China cap experiment.It's quite difficult to learn away from it if you've done it for living and long enough.For the point,I have a ticking 2215A, think it includes one of the early versions of that power supply.Ticking here is an own fault, mains into the machine from wrong spot.Possibly thru measuring tip shield, can't remember, is't a very long ago.Anyway, found the machine from the store after quite some time and thought I'll give it a try.It was a late night and I just plugged it in.Snap, silence, darkness.Heh,so far far away was it earlier.Couldn't remember it had a shorted primary, own fault that also.Finally quite easy to put those rectifier diodes to the wrong side of the board, must move them one day, no exceptions.One other thing I've forgotten.The problem of the power supply is also already solved, if memory serves.Before, when I had no papers, I really couldn't figure the thing out.After a tip from somewhere that you can drive it with external power the situation became much clearer.So it is proved I have a working scope with a faulty internal power supply, I think I've also read somewhere that there is a kit for totally bypassing the original.Now, when starting over I couldn't remember that eighter.Luckily DMM has that 'analog' thingy below numbers, should be a law.Anyway,all secondary voltages were pulsing.Clearly primary something problem and closer look revealed that many things were resoldered.Then more new recollections, I've once disassembed the machine quite a bit.Clearly also that letting time pass too much is not very good behaviour thingy.So the faulty one, C106B.The bugger crowbar was the problem.And then what, it's behind the frame.Now I remember why the machine was put aside.Oh BTW, just remembered that scope's piggy bag has a small plastic bag.Inside there are more smaller Tek plastic bags and there some small black things.After adding some visual aids I can conclude that I've found few measurement tip shield caps.

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 13, 2020, 03:54:24 am
content: Just finished the service bulletin upgrades with the resistor replacement, the jumper and the resistor/diode network jumper - so the PSU is now fully recapped with a few new transistors to boot (including the pre-reg which I thought was the problem at this point). Plugged it in, hit the button - no magic smoke!But - tick tick..... tick tick..... tick tick.....So now I guess I have a freshly recapped scope that's still dead. Time to FINALLY bust out the DVM and see what's up. Another day though, I'm tired!

author: mzacharias
author_rank: Frequent Contributor
timestamp: October 13, 2020, 12:55:51 pm
content: Okay, getting in late on this one, and not an expert on Teks' but after replacing the caps, and getting a "tick-tick"my suggestion is to look for shorts on the secondary side.I have often seen zener diodes for example placed across a power supply output, 5V, 18V, whatever. The zener is rated somewhat higher butwill short out as a crowbar if regulation is bad (bad caps) to protect downstream components; so after the caps are replaced one must then replace the shorted zener(in this scenario). The short could be farther down the line, a bad tantalum cap for example but this is where I would start.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 13, 2020, 06:13:17 pm
content: With an external 43V dc power supply, does it work or not ?

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 13, 2020, 07:07:29 pm
content: I don't have a supply big enough to test it. I have a Power One HC-48-1-AG which does 48VDC at only 1A.I'll look around for another supply. If it'll power up that way I might just bypass the entire factory PSU and run it on external power.

author: bd139
author_rank: Super Contributor
timestamp: October 13, 2020, 07:15:22 pm
content: 1A is probably enough. Think mine came up stable about 750mA at 43 volts. Theyre not particularly hungry scopes.Good idea bypassing it. I’ve considered that myself before. Meanwell unit also less likely to blow up in your face.

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 13, 2020, 08:36:57 pm
content: Only "problem" with the power one unit is it's currently housed in a nice plywood box along with another power one unit. The main one powers my Soundcraft Delta board and the 48V dude is all wired up to provide 48V phantom mic power. So I'd have to disassemble and disconnect... and I'd rather not.I'll look around for one of those meanwell units. They look small enough that they might fit inside the case.

author: bd139
author_rank: Super Contributor
timestamp: October 13, 2020, 08:52:29 pm
content: Should do. You may need to adjust the voltage divider resistors to get 43V out however. The 48V modules will go that low.

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 14, 2020, 04:51:29 am
content: Did a little more screwing around tonight and reading through the service manual - looked at a few things I either didn't replace or didn't get around to checking yet on the primary side.Zeners VR925/VR935 both test fine. C919/C907 (bd I know yours blew that one - the fat film one at the back) both test fine. CR907 also tests fine. I don't have an ESR meter but I have a generic capacitance meter and I didn't see any signs of leakage or meltdown on any of the caps I didn't replace.I also inspected the crap out of everything and noticed that CR851 is a diode/resistor network in series sticking up off the board that doesn't look factory, but might be. It's on the secondary side. I noticed it when I first opened the case, then forgot about it, then just saw it again. Duh.Finally, for grins, I unplugged all the jumpers feeding power and hit the switch and still tick tick... I wish it were possible to TOTALLY unplug the PSU from the rest of the bits to troubleshoot it all by itself.I think I'm in over my head on this thing.But if I feed it externally, to be clear - I hit it with +43VDC across TP940/950?

author: bd139
author_rank: Super Contributor
timestamp: October 14, 2020, 06:25:22 am
content: Re last point, yep that’s all you need to do is stick 43 volts across the two test points. Make sure they are the correct way round otherwise you’ll have even more problems.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 14, 2020, 07:13:07 am
content: the first question you should answer is : what is faulty ? the pre-regulator, the inverter or the crowbar protection circuit ?Try also to listen from what part is coming the clickThis is why whe asked you to feed the inverter with 43 Volts from an external power supply.

author: bd139
author_rank: Super Contributor
timestamp: October 14, 2020, 07:34:59 am
content: If it’s ticking it’ll be the preregulator. The secondary supply doesn’t tick.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 14, 2020, 08:43:25 am
content: Quote from: bd139 on October 14, 2020, 07:34:59 amWhen you make a diagnosis, you have to be 100% certain of what you say, otherwise, you risk heading down a dead end.It could also be an arc or hv leak for exampleThe only way to be sure is to supply the inverter with 43V, this is the way I have always used and which works perfectly.Now if you want to reinvent the wheel, it's your right.

author: m k
author_rank: Super Contributor
timestamp: October 14, 2020, 11:16:17 am
content: Are there still those HV side peak eaters that will blink with the ticking?

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: October 14, 2020, 06:29:55 pm
content: There are. I haven't noticed any blinking but I also had all the lights on.I think the ticking is coming from the U930 oscillator chip itself although I can't be 100% sure.Meanwell LRS-75-48 is a good candidate?https://www.mouser.com/ProductDetail/MEAN-WELL/LRS-75-48?qs=vDxCgdWo2h9ylXT4u%2FWpUA%3D%3D&gclid=CjwKCAjww5r8BRB6EiwArcckC9-xj6C-CKObqE_wUIighAHshsREIYlmy5S7IswAiqFA3mEaEqiZKRoCrUIQAvD_BwE

author: beanhauler
author_rank: Contributor
timestamp: October 24, 2020, 06:21:26 pm
content: Hi GuysI thought i would follow this up with some good news.As we know the original transformer in these is a 120-1594-00.In the manual it specifies changing to 120-1348-01 and an ebay member SHOCKCORE had one in the states although an 03 which is probably a revision code.Anyway fitted the new transformer and still no go, familiar click click. I was beginning to worry about the through holes in the vias that i had managed to rip out when i removed the transformer. It was a stubborn son of a....and i had to drill some aux holes and route some solid wire through it. Used a power suction pump as well.Looked up the spec of the transformer and the voltages were identical etc.Then i remembered the suggestion about using two back to back 30v power supplies on tp 940 and 950 the ground.This worked a treat , you can leave everything connected and just try and run the inverter. Came up no trouble but was arcing across the focus resistors. All sorts of weird corona discharges. Anyway on closer inspection i had used some copper pipe flux to soften the solder when checking the focus resistors and had not cleaned it up properly. 10 mins with a brush on a spray flux remover and all nice and clean and polished off with some pcb cleaner and an air pipe.Phew no more arcing. Let that be a lesson to me clean up after you. Both traces now up and running and all looking good.Anyway with the 43V and all connected all the power supplies out of the transformer were good to go ...did not check the HV but focus control in the middle and pin sharp so possibly ok. Check on current consumption on the 43V 670 mA which felt about ok @around 29W.Time for the big one. Variac and the mains...bingo! runs a treat.So as far as the strategy is concerned for the fault find for power click click. Before doing anything attach the 43V and check the volts out of the trans.No volts then check all the secondary diodes and caps. lift all the links one at a time see if it comes up. Dont forget to disconnect the flying lead to the multiplier. Still no go then change the transformer.If it does come up on the 43V but fails on the mains then disconnect the emitter resistor R949 and see if you get the 43V with mains connected.If not then follow the steps for the pre reg fault find as its likely Q9070 has died with some peripheral components.Hope it helps someone as this scope is just the nuts. Basic but the nuts.I am not sure how much longer these transformers are going to be available.I am seriously considering building a winding machine out of my steppers for the 3d printer ...good project i reckon but the tubes may have all died before i complete it. Todo list.Beanhaulernb spoke too soon. Got the tripping problem again but traced to the resistor R894 and 892. They are connected and the trace connects from lower board to upper board by VIA. Via was bad and causing bad contact and arcing which tripped the supply. May have been what caused the demise of the transformer.I think i will change these 510K resistors for the hell of it but it seems very stable now after a clean up and re-solder. On test now.Left all evening and ran fine but this morning familiar tick tick although the 5v led comes up briefly.Also the neons are flashing up.This is a strange one because if i run it up on the 43v it runs fine . Disconnect the 43v and attach th emains all good but let it go cold and no start.I am thinking this is an issue with the 510K focus resistors and the chain connected to the blanking.Think i will change all resistors and see what happens then.Will report back.Situation still continues with the scope not starting when cold.measured R860 which looked as if it had gone high at 8.6Meg so Changed and back to 6.2M. Still the same , Cold no go , give it 43V externally and warm it up and its fine as it will then rune off the mains. leave it for a bit to go cold and it wont start again. Familiar tick tick.I think i need to start using the freezer around some components to see if i can home in where the issue is .When its running on the mains its a little bit glitchy on the display even if the inputs are grounded. The dc on TP 940 and 950 sits at 42.4 rock solid though.This points to a problem on the HV side perhaps although have replaced all the 510k resistors and the two 5.1 k on the o/p of the multiplier.The crusade continues.The crusade is finally over.After application of some freezer around some of the components in its faulty condition i finally found it.Now it really all does make sense.I originally systematically removed each of the loads from the power transformer one at a time and still it failed to come up .I removed the HV supply and still no go. I missed something obvious and a crucial failure on my part....the intensity circuit or z axis is connected to two critical supplies via q845 and q840 and then is decoupled but referenced to the hv supply via C854 and some other caps but c854 takes the brunt of the voltage jump.It was arcing internally and externally underneath the cap when the HT was applied[see pictures.]I replaced the two 3KV capacitors and bobs your uncle. Runs from cold with the focus pot at half mast and nice sharp line.Note that i replaced C893 the other 1 nano cap decoupling the focus pot for good measure.Interestingly the caps were not short and on the cap meter read at 1.7n each. Goes to show that you need to check at full voltage and lv is meaningless.I have highlighted them on the diagram along with the resistor string.hope this helps anyone else who has the familiar click click.Incidentally i did replace a load of electrolytics when i started all this but it probably did no harm to change them all.Bottom picture shows the repaired 2235 running alongside the repaired 2211.The three white knobs on the 2211 are my 3D prints. Not as solid as the originals but do the job and clip in. Might try a cast resin to see if that is better.

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: November 06, 2020, 05:38:50 am
content: Finally got around to testing this out with an outboard Meanwell 48V PSU set to 43VDC and punched into the test points. I get a Tick, Tick, Tick... thought it sounded different than when trying to use the stock (but recapped and upgraded) PSU so I tested that again too as it's been awhile. That gives me a much fainter and more rapid tick tick...... tick tick.... tick tick....Where to go next...

author: m k
author_rank: Super Contributor
timestamp: November 06, 2020, 09:42:25 am
content: Even if you disconnect the original source you still have original all others, including that overvoltage protector.What is ticking?Put some more wires and eject the Meanwell.My prediction is that it's the powering transformer.Use peak-hold and check the voltage.Maybe that growbar is kicking in too early.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 06, 2020, 10:27:47 am
content: Quote from: Rickenbackerman on November 06, 2020, 05:38:50 amThe speed of the tick..tick depends on the supply voltage, so nothing can be deduced from it.This tick ..tick means that the inverter (T948) is trying to start but it is overloaded.Unsolder the HV U975 multiplier and check whether the tick tick continues or not.If it continues, check for dead short circuit all the secondary diodes (CR954, CR955, CR956, CR957, CR960, CR961, CR962, CR963, CR967, CR970 and check if there is no short circuit on C954, C956, C960, C961, C968. (NB: NOT dessolder those capacitors !!!!)

author: m k
author_rank: Super Contributor
timestamp: November 06, 2020, 08:55:19 pm
content: Quote from: akimpowerscr on November 06, 2020, 10:27:47 amCan fainter and more rapid mean less overloaded?

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 06, 2020, 10:22:01 pm
content: No, moreover, in most cases, the cause is a short circuit in one of the circuits connected to the secondary of the transformer.

author: m k
author_rank: Super Contributor
timestamp: November 07, 2020, 09:21:49 am
content: Do I understand the situation correctly.#43With Meanwell, ok.Without Meanwell, ok until cold.#44With Meanwell, bad and ticking differently.Without Meanwell, bad and fainter and more rapid ticking.So Meanwell can't handle it anymore and own power is also ticking differently than before?

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: November 20, 2020, 05:23:48 am
content: Quote from: m k on November 07, 2020, 09:21:49 amI can't comment on post #43, not sure why beanhauler posted in my thread (which is totally okay! we're all here to fix stuff!), but for post # 44, yes, with the Meanwell I get a slow, somewhat louder tick.... tick.... tick.... and with the 2235 PSU I get a faint and VERY rapid tick tick.... tick tick.... tick tick...Quote from: akimpowerscr on November 06, 2020, 10:27:47 amOnly had a few minutes tonight to do some more testing. I tested all 10 diodes, they all seem fine. I didn't check any of the caps as they have all been replaced already during my recapping procedure. I didn't unsolder the HV U975 multiplier and retest as I didn't have time and was hoping I'd find a bad diode, which I didn't. So, the hunt continues...

author: beanhauler
author_rank: Contributor
timestamp: November 20, 2020, 08:21:55 pm
content: Apologies for that ....still trying to get to grips with this forum!If you cant get the 43v external power supply to run it then you need to lift up each of the links in turn on the 100/30/8.6/-8.6/ and 5v links that are on the board. Watch the sneaky 5 v pre link off to the other boards.Do the last 5v link last as the led is powred from it and there is no indication that the power trans is working unless you monitor the other rails.If that fails then disconnect the hv tap from the power trans to the mult and then also lift C854.Check then and see if the led lights up. If it does look for short C854 or the focus resistor paths.This of course is all dependent on the smoothing c's and diodes around each of the o/ps being ok as Rickenbackerman says!If they are then it may be a spent transformer

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: November 21, 2020, 05:08:50 am
content: beanhauler, no worries on posting here! And thanks for your help!So when you say "lift up the links" - are you are referring to W954(100V), W956(30V), W960(+8.6V) and W968(5V) on page 15 of the service manual attachment you posted? If so, this is where things get dicey. I don't see the -8.6V link on that page AND my PCB doesn't even match what's on that page either. Some of the links are in different places, but at least they're all labeled on the board. I posted a pic of that area of my board below, first time posting a picture, hope I didn't hose things up...To be clear, am I just lifting links one at a time and trying to get rid of the tick tick and get the power LED to come on? Need to take my time here as I suspect I'm in over my head.Oh I checked the four 510K focus resistors tonight since I knew it would take 30 seconds, they all test fine, 510 to 520K. If I can get this damn thing running I'll replace them anyway since I have new ones already sitting here. Tested C854 for a short while I was at it, didn't test for capacitance but it's definitely not shorted.

author: m k
author_rank: Super Contributor
timestamp: November 21, 2020, 10:59:33 am
content: How you disconnected the original power when Meanwell was in use?If your multimeter has ranges you can check where and what range goes over with ticking.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 21, 2020, 12:37:01 pm
content: Quote from: m k on November 21, 2020, 10:59:33 amNo need to disconnect the pre-regulator.

author: m k
author_rank: Super Contributor
timestamp: November 21, 2020, 07:42:51 pm
content: Yes, ground is pretty far from anything.Vivid recollection was probably something precautious.Yet I'm still wondering can the original crowbar make all of those tickings.

author: beanhauler
author_rank: Contributor
timestamp: November 27, 2020, 01:01:27 am
content: Step back a bit.remove external supply and lift R949. measure it should be close to 1 ohm. leave it openHook up a dvm across the two test points and p[lug in the mainsCheck you have close to 43v and no ticking.Unplug the mains if good.resolder R 949 IF ALL GOOD.Hook up your 43v supply to the two test points and watch the polarity as per the diagram.Make sure all the links are in place and monitor current and voltage on test supply [i use two dvms]as you slowly wind up the voltage.If it makes a move towards an amp then back it off.Lift your w links one at a time and do the same procedure each time.Do teh 5v rail last as you are using the led to see if teh 5v rail is coming up.see where it gets you. Document results of each lift.

author: Rickenbackerman
author_rank: Regular Contributor
timestamp: November 28, 2020, 04:51:49 am
content: beanhauler - these links you speak of - I asked in my last post but maybe you didn't see the question -"when you say "lift up the links" - are you are referring to W954(100V), W956(30V), W960(+8.6V) and W968(5V) on page 15 of the service manual attachment you posted?"The meanwell PSU I bought is a switcher so no bringing it up slowly, although I do have a variac if I want to try using the stock PSU to come up slowly...

author: m k
author_rank: Super Contributor
timestamp: November 28, 2020, 12:31:55 pm
content: In case you're missing peak-hold consider Dave's #490.Orhttps://sound-au.com/appnotes/an014.htmIf you can't get the ticking go away you need to know what it actually is.Like over or under voltage or something in between.Voltage over the current sense is not a bad thing to know eighter.

author: beanhauler
author_rank: Contributor
timestamp: November 28, 2020, 03:23:37 pm
content: Variac on the front of a switcher wont work as they usually wont start until it gets to 80 V or so.Dont try it on the other side it should be dc:-)Reading your mail again i see you are talking about winding the mains incoming up and downNot at this stage. Dont bother. get the 43V rail humming first. If that works and drives the scope then you need the variac.If you put the variac on the front the pre reg waits for a sufficient voltage and then tick tick.....yes the links are the w links .dont forget the -8.6 v rail as well...very important rail.Go to page 14 of the pdf i sent you.The little diamonds on the sheet show you where the connections come from...so sheet 7 or sheet 8 etcyou will find all the connections on this sheetMAKE SURE R949 HAS ONE LEG UP IN THE AIR. SET YOUR SWITCHER O/P TO 43V OR A LITTLE LESS.If its a switcher and you cant bring it up slowly dont worry.Connect between the two test points by inserting a 60w incandescent bulb in the way to limit current. and flick on and measuer current draw and voltage. TP 950 AND 940. 940 IS THE PLUS CONNECTION. check current is low...i mean low. well under 100mA.IF OK then proceed. SWITCH OFF REMOVE THE LAMP.RECONNECT WITHOUT.DONT WORRY ABOUT THE W LINKS AT THIS STAGE AS LONG AS R949 IS OPEN CIRCUIT#MEASURE THE VOLTAGE ......AND MAKE SURE ITS 43 V WITH LITTLE CURRENT DRAW. IF ITS NOT 43V THEN ADVISE ON THIS THREAD.SWITCH OFF and wait a couple of mins and put R949 BACK IN CIRCUIT.Start lifting your w links one at a time the 5v rail the last to lift. Actually do the flying lead to teh multiplier first and see if the 5v rail comes up by watching the led on the front. Same procedure lift w954/955 100v rail etc. Watch your pinkies 2KV is in action here and it hurts/kills.did not come up? Check all resistors in CRT circuit including those in the Z circuit and especially the diodes.Went through the lot and still no go?Check the transistors Q946 Q947 as a last ditch and if they look OK...assuming you know how to test base emitter/base collector else replace them.Make sure that your PS is good for 1 amp at 43V and always monitor the volts/current at the primARY tp940 tp 950.If it dips or current increases beyond 800mA switch off and investigate.It could be that the inverter is refusing to run in which case it may be shorted primary...really unlikely but possible...shorted HV 2K Internal. This is a real possibility and my experience so far is that if you measure the secondary pin 23.....the flying lead..to the ground....pin 10 it should be below 500 ohms or so ..actually my original transformer measured just about a zillion ohms as the connection internally wheer its soldered to the insulated wire where it exits had got hot and melted the solder. Also shorted internallyActually i'm going to calculate from the number of turns and wire size what it should be...back in a min.The HV wind is 1025 T #39 for a voltage of -2050Vcheck my math someone:-)#39 awg= 2.73 ohms per metredia on this transformer i estimate as 30mm therfore 1 turn approx 94 mm= 1025*94=96350mm/1000 or 96.350 metersmult this by 2.73= approx 263 ohmsWHICH IS INTERESTING AS THE SPEC FOR THE TRANSFORMER LISTS IT AS 50---->>>>800 OHMSBIT WIDE FOR MY LIKING BUT EITHER WAY IF ITS ABOVE A K THEN YOU HAVE TROUBLES.Attached a pdf of some details about the transformer...enjoy.

author: robbie1949
author_rank: Newbie
timestamp: August 26, 2022, 07:52:09 pm
content: I guess it's because these people don't know anything about logical fault finding, only replace capacitors if testing reveals it is leaky or has high ESR.I am fault finding a 2235 power supply at the moment. To start with the preregulator would start only to shut down and kept cycling like this. I have disabled the inverter and now the preregulator stays up. The fault is in the inverter or high current drawn on the output secondaries of the inverter transformer T948, or indeed T948 itself breaking down internally causing the inverter to draw excessive current. I will update when I have found the problem.

author: floobydust
author_rank: Super Contributor
timestamp: August 26, 2022, 08:49:54 pm
content: Quote from: robbie1949 on August 26, 2022, 07:52:09 pmI say "no" - outright replace antique electrolytic capacitors in 2235 PSU, they are almost 40 years old. Some people like to spend hours and troubleshoot down to the exact part, only to have to replace another cap a year later. Many are cracked and leaking yet can fool a person for ESR and capacitance. For your time and hassle, spend the $20. The Sangamo's don't last.https://www.eevblog.com/forum/repair/tektronix-an-usm-4882235-high-8-6-v-ripple/msg2539461/#msg2539461has 2235/2235B replacement capacitor list.

author: David Hess
author_rank: Super Contributor
timestamp: August 27, 2022, 07:54:16 pm
content: I agree; when they are that old, replace all of the aluminum electrolytic capacitors whether they test bad or not.