Thoughts on buying "non-working" or "for-parts" Oscilloscopes? - Page 1
Forum section: electronics / general

author: FenderBender
author_rank: Super Contributor
timestamp: November 22, 2011, 02:03:47 am
content: I've only been doing this electronics thing for about 2 years now, but I've come to understand how electronics are rarely everbrokeneven when they are "broken". You can usually fix stuff. Likely candidates being a bad power supply capacitor or some dead silicon. Only under some pretty rare circumstances is it ever catastrophic enough to not bother with...or if you were looking for an excuse to get rid of it anyway...So I was looking at some older scopes: Tek 2465, 2225, 465 etc on eBay. I could get a freshly calibrated 2465 for like $800, while I could get a "for-parts" scope for $250.Are there ever problems with these types of scopes were repair is impractical or impossible? Some things I'm aware of with older Tek scopes are bad "wet-type" tantalums, overheating chips, dead power supply capacitors, bad switches, attenuators, encoders etc.Aside from the unit-specific parts like the switches and stuff, replacing a cap here or there shouldn't be that expensive.My question is: Do you think it would be worth it to take a risk and buy a scope that the seller says doesn't work, and then try to fix it yourself?

author: Psi
author_rank: Super Contributor
timestamp: November 22, 2011, 02:21:29 am
content: It's the unit specific ICs you have to watch.Sometimes they just don't exist any more and are not available anywhere.You can hack up a replacement switch with maybe a few relays to create custom contacts but is much harder to make a new circuit to replace a dead IC that's not available.Of course not all scopes use customs chips, my old analog scope is all generic opamps and 4000 series logic.If you plan on buying a scope to repair you should find a copy of the service manual/schematics first. If one isn't available i wouldn't bother getting the scope.You can also use it to check what kind of custom IC's the scope has, (if any), before you buy.

author: joelby
author_rank: Frequent Contributor
timestamp: November 22, 2011, 02:23:55 am
content: It depends if your aim is to get a cheap oscilloscope, or if you just enjoy fixing broken oscilloscopes. Some parts may be proprietary, obsolete and impossible to get, so you might need to combine several broken units to get one working one. Service manuals might be difficult to obtain.

author: FenderBender
author_rank: Super Contributor
timestamp: November 22, 2011, 03:01:43 am
content: Oh yes..I forgot about those crazy 40-Pin DIPs with exotic part numbers. Hmmm...well I'm actually leaning towards a $175 working Tek 2225 that I found on eBay. 2 Channels @ 50Mhz is nothing special, but it's about 1/2 the price of a Chinese DSO with similar specs. Not bad.

author: amspire
author_rank: Super Contributor
timestamp: November 22, 2011, 04:03:16 am
content: "For Parts" can often mean parts are missing. Someone may have already taken out some of the best parts, and they are now selling what is left."For Parts" usually means the seller doesn't think it is suitable for repair, so you have to be careful.Richard

author: JonnyBoats
author_rank: Regular Contributor
timestamp: November 22, 2011, 04:14:18 am
content: If you are considering an older Tektronx unit you should definitely checkouthttp://tech.groups.yahoo.com/group/TekScopes/This is where all the experts on older Tektronix equipment hang out and they will be more than happy to answer your questions and are the best source for esoteric information.Some items are much easier to fix than others, and unavailability of custom ICs and other parts can be a real issue.

author: scopeman
author_rank: Frequent Contributor
timestamp: November 22, 2011, 04:18:23 am
content: Hello FenderBender et al,Well I hope I don't get too long winded with this but my passion for scopes gets the best of me sometimes. The discussion below is aimed at analog scopes. Every bench needs at least one really good analog scope.As far as buying broken scopes that all depends on what you really want to get out of it. I have been collecting, repairing and modifying scopes since I was 10 years old. At 9 I had the only oscilloscope on the block, a Hickok vintage 1947 model. I though that I had died and gone to heaven that Christmas morning when I woke up and my Mom and Dad gave me that scope. The tag said Santa but I was already wise to Santa's ways! To me it was better than Ralphie's Red Rider BB gun (which never existed before the movie, but that is another story!).Since then I have owned just about any scope you can name at one time or another. Nearly all of them needed some sort of repair or recalibration or whatever.To me these great machines are much more than tools, they became my "eyes" enabling me to watch the world of moving electrons, in hopes that I might learn how to control a few!I read the manuals and schematics by flashlight after "lights out". I think that my parents did not mind so much as I always had a supply of batteries!I learned much from reading these manuals from cover to cover. Sometime around 8th grade my Dad ran into a guy who dealt in government surplus and he had a bunch of Tek 547A's. Some worked, some did not. This fellow was a dealer but he did not know much of anything about scopes. My Dad suggested to him that I could help him fix his scopes and that maybe he would be interested in working a deal on a scope if I could fix his broken ones.Well at the beginning I did not know very much about those hybrid scopes, much less what a tunnel diode was but when I was done I had fixed 35 out of the 50 or so he had and calibrated the 15 good ones over one summer.I ended up with two good 547A's (I still have one of them). The scope deal was great but the education from fixing them was the best return on a summer vacation that I ever had. I can without a doubt say that that experience was the pivotal point in my life that led me to become an electrical engineer.All that aside If you are looking for a great analog scope that is easy to repair I would recommend a Tek 453/453A/454/454A. 50MHz, 60MHz, 150MHz? and 150MHz.The A models are all solid state (some of the non A models are all solid state as well but if I remember correctly the serial number must be above 20,000). The top and bottom covers on the hybrid models (contains nuvistors) have more ventilation holes. I would not totally discount owning the nuvistor ones (I still have a couple) as they are very hard to damage the front end. They take about an hour to totally stablize but they are still great scopes.If you have a choice go for the A models.I recommend this series to a beginner (especially if you are buying a broken one) since they contain no special IC's. They are totally built from discrete transistors and diodes. True they have tunnel diode triggering but failures of these diodes are rare and you can still obtain them if you know where to look. In addition the manuals are excellent, some of the best technical manuals ever published. Even if you never buy one the manual for the Tek 454A is a great read.These scopes can be had at hamfests and flea markets for as little as 50.00. I once bought a Tek 422A at my local flea market for $15.00 and it still works. It is my loaner scope. King Kong could not kill it.Try and find one that will at a minimum display a beam or better yet a trace. Good CRT's are a little tough to find.One really great thing about this series is the CRT "spot size" a good CRT should have a very sharp defined trace. Perfect ones show little "blooming" at high intensity levels. Due to the age of these scopes I would expect a little blooming.If you want to move up the ladder for a higher bandwidth go for a Tek 465/465A/475/475A 100MHz/100MHz/200MHz/250MHz. The caveat here is make sure that you understand that this series contains specialized IC's that are a little hard to find. Also I have seen a few that have had issues with CRT damage if they have been dropped so inspect them very carefully. Even if one has been dropped it is still good for parts. These scopes were produced in huge quantities so parts are plentiful. I have even seen new CRT's on ebay.These scopes can be had cheaply on ebay. Often the shipping may cost you as much as the bid price.But a Tek scope of this vintage is worth much more than any other import analog scope.I would not recommend HP scopes from this era as they typically did not have CRT's that were equal to the Tek models. They made some great scopes (1740A, 180/182) but they never were the equals of the analog Tek's.Stay away from all analog storage scopes as they were a problem in themselves.I do not recommend the Tek 7000 series to beginners but that being said there are some great bargains out there if you want and need the flexibility the 7K series gives.I would recommend the 7704A 200 to 200MHz and the 7904A 500MHz. As for plug-ins you will have to do your own research on that. You can find tons of info on the net. There are even some digitizer plug-ins that will work with this series.For service you will need a set of plug in extenders or a spare set of plug ins.You can probably pick up a complete 7000 series scope with plugins for under 200.00 maybe a lot less.In closing you might ask "If I have a digital scope, why would I need an analog scope?". The answer is a little complex but let me list a few bullet points. I am not talking about a comparison to multi-kilobuck digital scopes only the low cost ones you see.1. An analog scope will show you (within the limits of the instrument + probe bandwidth) exactly what the signallooks like as there is no computer interpreting the signal as in a digital scope.2. The signal fidelity is very faithful to the actual signal on an analog scope.3. Generally an analog scope has a lower noise floor and it is easier to discern when the signal comes out of the noise floor,4. To get a digital scope that has the same useful bandwidth as a 100MHz scope requires a scope with at least a 1G/sample/second digitizer and at that rate on a 100MHz signal (in single shot mode) you only will get 10 samples per period of the 100MHz signal. Digital scopes are much better for repetitive signals as they can overlay the data using other than single shot sampling.5. The dead time between sweeps is very low with an analog scope yielding a very high update rate. Signals like live video look like live video.6. The vertical dynamic range is very high with a good analog scope. You can drive the signal way off of the screen to look at details that are hard to see otherwise. Many of the Tek scopes can be driven 5 or more total screen heights without driving the vertical amplifier into clipping and even then you can still look at the edges or sides of the waveform. I don't believe that any current digital scope is equal to this task. That is one of the reasons that the late Jim Williams appreciated the design of the Tek 547A so much. It's hybrid design yielded a net dynamic range higher than any other analog scope (depending on the plug-in used).7. Good used analog Tek scopes are so cheap these days every bench should have at least one, even if you own a great LeCroy digital scope! :-))I am sure that I could think of at least a dozen more reasons, but I have to sleep sometime!All the best and I wish you great scope hunting!Sam

author: SgtRock
author_rank: Unknown
timestamp: November 22, 2011, 04:58:23 am
content: Dear Sam (Scopeman):--Thanks for the entertaining, interesting and informative post.--I was able to get my neighbor's Fluke 77 DMM back into operation by replacing the DAC chip. I then cleaned it calibrated it, replaced the missing screws and polished the windshield. He ended up giving me a Tek 545 and a manual for a 545A. The scope supposedly only needs a couple of tubes. I just wanted to ask you what the difference between the 545 and the 545A is; and ask for any thoughts you may have on reconditioning a 545.--Thanks again for the excellent post, and don't put your eye out."In the heat of battle, my father wove a tapestry of obscenity that as far as we know, is still hanging in space over Lake Michigan."Ralphie ParkerBest RegardsClear Ether

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: November 22, 2011, 07:00:48 am
content: Quote from: amspire on November 22, 2011, 04:03:16 amI learned this the hard way from local auctions.

author: david77
author_rank: Frequent Contributor
timestamp: November 22, 2011, 07:20:42 am
content: I would not buy a scope that does absolutely nothing, it should at least show a trace or a bright dot on the CRT, that way you can be pretty certain the tube and the HT are still working. If the scope shows no signs of life and is free/very cheap it is worth the risk, you can always bin it if a repair isn't possible.So far I've only worked on European scopes, some older Hamegs and a Philips. These were rather low end scopes around the 20-50MHz mark and they had no special parts in them. Apart from the switches and HT transformers all standard components that have been around for decades.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 22, 2011, 09:39:48 am
content: Something to consider is that test gear is unlike other electronics in that most users will be engineers and will already have attempted to repair it, so items sold as faulty are more likely to have serious/fatal issues than, say a camcorder or other consumer electronics.I'd also suggest that anything described as 'for parts' as opposed to 'faulty', 'broken, 'damaged' will typically mean beyond repair and/or parts missing.If it's cheap enough that you can afford to write off the money, by all means go for it.

author: saturation
author_rank: Super Contributor
timestamp: November 22, 2011, 10:47:21 am
content: Great post, scopeman, your name is well deserved. This post should be standard reading for anyone looking for an analog scope.I haven't heard 'solid state' used in decades, so I'm guessing you must have grown up during the transition from tubes to discrete seminconductors. Those were the days when most small batteries began to be referred to as 'transistor batteries', small being the common 'D' cell size!Quote from: scopeman on November 22, 2011, 04:18:23 am

author: EEVblog
author_rank: Unknown
timestamp: November 22, 2011, 11:15:29 am
content: Quote from: scopeman on November 22, 2011, 04:18:23 amAwesome post Sam, thanks for sharing.I almost hate to ask how many scopes you have?, I'm sensing one big-arse collection!If so, any photos to share?Dave.

author: saturation
author_rank: Super Contributor
timestamp: November 22, 2011, 12:22:22 pm
content: Yes, that would be very interesting, a tek version of excavortee's fluke collection:Quote from: EEVblog on November 22, 2011, 11:15:29 am

author: don.r
author_rank: Frequent Contributor
timestamp: November 23, 2011, 03:45:07 am
content: Just a note to the OP to be patient and use a sniping service like gixen.com to get the best deal. I snagged a beautiful Tek 2225 for less than $200 on eBay a while back and just got myself a mint 2245A for just a hair more recently (with a probe!). Be patient, look around (local sales and whatnot), and you will eventually find that gem. I, personally, would not want a parts scope for my first scope as you would probably need a working on to fix it.

author: joedevola
author_rank: Contributor
timestamp: November 23, 2011, 07:11:34 am
content: G'Day scopeman,Seeing you are the resident guru, I thought I might ask a quick question if I may...My 16 year old son is showing an interest in electronics, so I bought him a second hand scope, a Tek TAS 455 (found very cheap on ebay). Worked when I picked it up and when I got it home, but when I presented to son (for his birthday), it would not trigger. As I am pretty new to electronics myself, I am a little stumped as to where to start to attack this problem. I tried on the yahoo groups thing, but my computer skills led me to frustration with the format of that forum. It is not as easy to navigate and use as this and DIYAudio etc... I downloaded the service manual, but the manual I found pretty much stated a trouble shooting procedure to work out which board to replace, rather than repair.Any assistance or hints very much appreciated!Cheers,Chris

author: scopeman
author_rank: Frequent Contributor
timestamp: November 23, 2011, 04:14:33 pm
content: Hi Chris,I have a TAS485 I picked up a while back but I did not have to do too much to fix it so I don't have a lot of stick time on these.The nice thing about the TAS485 is it is the only 4 channel portable analog scope that has 4 channels that has full attenuators with a 2mV lower scale. Great for analog work.I don't think your TAS should be too hard to fix. I hope that it is not one of the special IC's. Be on the lookout for leaking surface mount electrolytic capacitors (these were a plague in the 24X5B A5 Board - the only place Tek used them in this scope).The manuals are a bit hard to find but check out the link below for a TAS465 manual which I believe is the same except for bandwidth. I probably have more operators manuals on this unit as well. Contact me off list and I will see what I can do.I would check to see if the scope will trigger on any channel or on external trigger. Make sure that you have the LF/HF reject turned off as that may be an issue depending on the signal you are using.Also check out the TekScopes group on Yahoo. I think that Stan Griffiths (a long term Tek Employee) still hang out there and I remember reading that he had repaired a bunch of these scopes under contract to Tek at one time.http://manoman.sqhill.com/pdf/tek-tas465.pdfSamScopeman

author: scopeman
author_rank: Frequent Contributor
timestamp: November 23, 2011, 05:15:39 pm
content: Quote from: EEVblog on November 22, 2011, 11:15:29 amHi Dave,Now I will have to sit down and compile a list. I would guess probably close to a hundred if you include dead ones that I could not pass up that I have not gotten around to fixing. I don't currently have any pictures. I guess I have to stack them up someday. Off the top of my head the working ones are:Tek214335422A(2)453453A454A465465A465B475A DM44TAS485547A with a bunch of plugins (currently it has a bad HV xfmr)2465 (2)THS710TDS220 w/MMTDS224 w/MM7603 (3 units 1 new in box)R76037704A (2)7904A bunch of 7K plug-ins7D20 digitizer (3)7L14 SAHP Analog1200A1220A1740A (mint - left to me by a long gone friend who bought it new from HP) I don't loan this one!853A with a dead 8559I had a HP54501A but I sold it a while back.HP54503A (has issues)LeCroy DSO94009410ALS1409314AL9354AL (one of my favorites)LC574AL (like a color 9384C)WaveRunner 1 200MHz 4 ChannelWaveRunner 2 1GHz 4 ChannelWaveJet 324LeCroy Analog LA314 (actually an Iwatsu SS-7840) 400MHz Quad Channel. A really nice scope and they go cheap on ebay.Nicolet204204A3091? rack mount that is branded Instron.Hantek 1060Owon PDS5022 with a chinese faceplate. The SDS6062 scope is light years ahead of this entry level scope in all respects.I have started to pair down my inventory a bit. Some of the ones on the list are out on loan or at my company being dedicated to projects.So Dave did you get the LeCroy 9384C working and did you get the off list email I sent you on it?Happy Scopeing!!!Sam

author: don.r
author_rank: Frequent Contributor
timestamp: November 23, 2011, 06:13:12 pm
content: Holy crap!And I was agonizing over buying asecondscope!

author: saturation
author_rank: Super Contributor
timestamp: November 23, 2011, 08:05:09 pm
content: Amazing, scopeman is to scopes as excavortee is to fluke dmms. Some pics would be nice.Quote from: scopeman on November 23, 2011, 05:15:39 pm

author: joedevola
author_rank: Contributor
timestamp: November 25, 2011, 02:06:20 am
content: Thanks for the help Sam,In the middle of exams at the moment, so will get the scope on the bench again next week and report back.Cheers,Chris

author: scopeman
author_rank: Frequent Contributor
timestamp: November 25, 2011, 06:20:38 am
content: Hi Chris,I have a PCB file to get out tomorrow. Once I get that done I'll dig the TAS465 manual out and see ifI can come up with any more tips.Sam

author: FenderBender
author_rank: Super Contributor
timestamp: December 19, 2011, 12:22:39 am
content: Well it's almost Christmas so better treat myself to something nice. I'm looking at a 465B or 465M. I can get the M for a little cheaper. I know the 465M is essentially a rebadged 455, but for "military use". Whether that means it's more reliable, only Tektronix knows. If I could score one of these for under $100, working, that would be sweet. I'm a noob to oscopes but these are "simple" enough to try to fix if I needed to...(simple is relative).So let's see!

author: FenderBender
author_rank: Super Contributor
timestamp: December 19, 2011, 04:23:25 am
content: God damn...

author: don.r
author_rank: Frequent Contributor
timestamp: December 19, 2011, 05:27:09 am
content: Quote from: FenderBender on December 19, 2011, 04:23:25 amYep. Nice and straightforward.... not much in there that you can fix yourself.

author: tekfan
author_rank: Frequent Contributor
timestamp: December 19, 2011, 12:45:12 pm
content: Quote from: don.r on December 19, 2011, 05:27:09 amWell at least the power supply is a linear and not switchmode type like in some of the 2200 and 2400 series.The vertical output amplifier is also very straightforward and without the usual custom Tek ICs.

author: don.r
author_rank: Frequent Contributor
timestamp: December 19, 2011, 04:02:17 pm
content: Quote from: tekfan on December 19, 2011, 12:45:12 pmMy mistake. I meant to type "can'tfix yourself." One of the best reasons to buy scopes of this era. Few customs and lots of big through-hole discretes.

author: FenderBender
author_rank: Super Contributor
timestamp: December 19, 2011, 09:06:30 pm
content: I'm looking at one on eBay. Pictures show two traces on the screen so I'm assuming that nothing is really wrong with it. See if I can score it! Maybe a power supply filter cap or two needs to be replaced. Or some other discretes...Tek cathode tubes are good...so I hope I wont have to replace that...

author: don.r
author_rank: Frequent Contributor
timestamp: December 19, 2011, 09:13:15 pm
content: Two traces show that at least the horizontal amps work. If the trace is fairly sharp and bright and there is no burn-in, the tube should be good for a while. It may need to be calibrated but you can do that yourself to a good degree if you have a function generator or other waveform source (even a PC sound card will do). Good luck and don't overspend!

author: FenderBender
author_rank: Super Contributor
timestamp: December 19, 2011, 10:01:15 pm
content: Auction ends soon. Hopefully I can get it for under $100. Pretty sure I can win it. First scope! Fingers crossed!

author: FenderBender
author_rank: Super Contributor
timestamp: December 19, 2011, 10:21:21 pm
content: Speaking of function generators...any suggestions on some good function generators maybe the same vintage as this scope?

author: don.r
author_rank: Frequent Contributor
timestamp: December 19, 2011, 11:30:30 pm
content: Quote from: FenderBender on December 19, 2011, 10:21:21 pmI'm partial to anything made by Wavetek. Lots of documentation online including schematics and trouble-shooting flow charts, very well labelled boards.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: December 19, 2011, 11:33:07 pm
content: For Euroland the best name for easy repair about the oldies is Hameg.You can find lots of parts for them, and repair manuals.

author: FenderBender
author_rank: Super Contributor
timestamp: December 20, 2011, 01:24:15 am
content: Woot woot! Won the auction! Looks like I'm getting a working 465M for $79.99 shipped!

author: ivan747
author_rank: Super Contributor
timestamp: December 20, 2011, 02:20:25 am
content: Cool, too bad I would have to pay THAT price for shipping the scope here.Interestingly enough, the other day I found out that shipping to China from the US was cheaper then shipping to the Dominican Republic. The DR is just two hours away, whereas China is 10+ hours away.

author: FenderBender
author_rank: Super Contributor
timestamp: December 20, 2011, 02:28:55 am
content: Yeah that's unfortunate. My guess is that since there is much more import/export between China and the US than between DR and the US that prices are lower.I paid $40 for shipping. $40 for the scope. It's actually coming from Canada.

author: BravoV
author_rank: Super Contributor
timestamp: December 20, 2011, 02:40:20 am
content: Congrats, nice catch.Now you owe us all a full tear down and expecting lotsa pics.

author: FenderBender
author_rank: Super Contributor
timestamp: December 20, 2011, 02:48:31 am
content: Totally. I'll probably be opening this bad boy to check for some cleaning and to check if anything needs replacing/rejuvenating.Only thing I'm worried about are those crazy range switches that I'm pretty sure are proprietary. Hopefully they aren't dead.No probes are coming with it...And I've never had an o-scope before...Maybe I'm being ignorant, but $150 for some Tek probes seems silly when I'm paying $80 for the scope itself. Maybe someone could point me to a buying guide.

author: IanB
author_rank: Super Contributor
timestamp: December 20, 2011, 03:04:27 am
content: Quote from: FenderBender on December 20, 2011, 02:48:31 amHere's one on clearance for 20 cents:http://www.frys.com/product/2379089If you are near a Fry's you could check and see if they have any left...

author: BravoV
author_rank: Super Contributor
timestamp: December 20, 2011, 03:14:45 am
content: Quote from: FenderBender on December 20, 2011, 02:48:31 amJust becareful when working at those old plastics, some of them might be aged enough that is very brittle.Quote from: FenderBender on December 20, 2011, 02:48:31 amSince this is your 1st, suggesting not to invest on expensive probe now and do it later, just buy those cheap but new 100Mhz, and play with it 1st until you really need to go into full scope's bandwidth capable probes.Unfortunately a really good probe is still quite expensive even used, but once you've seen crap probe and hook up good probe at the same signal, especially on a good ole analog scope, it will be an eyes opener, they're like night and day.Instead of investing heavily on expensive probes for beginner, I highly recommend you to look and hunt for a good priced isolation transformer, trust me, this thing will be your scope's sidekick that you can't live without it.Hunting or even stalking a good probe is quite time consuming if you're looking for a good one but cheap, for example like mine here ->https://www.eevblog.com/forum/index.php?topic=5756.msg75090#msg75090, it took me almost 3 months and luck of course, to score them at ebay for about the same price as your scope.

author: The_Penguin
author_rank: Regular Contributor
timestamp: December 20, 2011, 03:22:33 am
content: Quote from: FenderBender on December 20, 2011, 02:28:55 amSweet, congrats! Wonder how I missed that one, I've been watching scopes and generators on Ebay for a week or so.I don't recall seeing a Canadian one, don't see it in completed listings either...Not that I'd have nabbed it, my next scope is likely a Rigol.

author: PStevenson
author_rank: Regular Contributor
timestamp: December 20, 2011, 01:32:34 pm
content: I quite often buy the broken scopes - I remember reading an article written by this old engineer (I forget who now) but he said when he started working in this lab they would give him a budget for anything apart from repairs because they said the engineer would learn faster if he had to trouble shoot any broken equipment rather than just repair it. obviously in this day and age it's not always possible with custom ICs and so on (mentioned earlier in this post) but with the older analogue scopes there's always a pretty good chance of repair if you stick at it.someone raised one good point that most of the time this type of equipment comes from experienced technicians/engineers who tried to repair it already but couldn't so it's probably dead for good however 2 things were overlooked here 1. the more experienced engineers tend to be less motivated to fix these things (I've often heard the words "I can't be arsed") sometimes they can be arsed until they open it up and see those big rotary switches locked in place by a million wires and then their motivation shifts to "I can't be arsed" another more common thing (2) is that the scope was stuck in someones dads shed for 30 years and once the dad died they stuck these things on eBay knowing nothing of what they do, often turning it on with the position knobs all the way up so there's no trace, seeing it do nothing and assuming it's broken. I've bought quite a few "for parts" scopes from eBay most I have fixed, one I keep going back to - opening it up and then thinking "I can't be arsed" and another one I haven't gotten around to yet. oddly enough the 2 most recent that I fixed were both philips and both had exploded electrolytic suppression capacitors.so my view is that if you are comfortable enough try to fix the broken ones cause it's always a good addition to the knowledge you have already gained.as for the digital ones, I might check voltages and peruse it a bit but I'm way out of my depth with digital stuff really

author: tekfan
author_rank: Frequent Contributor
timestamp: December 20, 2011, 02:10:26 pm
content: Quote from: PStevenson on December 20, 2011, 01:32:34 pmThere's always the chip swapping technique if everything else fails. You don't really learn why the thing failed but most of the time you get it fixed.Quote from: PStevenson on December 20, 2011, 01:32:34 pmMay I ask which scope would that be?

author: PStevenson
author_rank: Regular Contributor
timestamp: December 20, 2011, 04:42:37 pm
content: Quote from: tekfan on December 20, 2011, 02:10:26 pmsure, it's the telequipment D67.I've never had much luck with shotgunning stuff but I can see standing a better chance of fixing something I don't understand with that method

author: don.r
author_rank: Frequent Contributor
timestamp: December 20, 2011, 04:45:20 pm
content: Quote from: PStevenson on December 20, 2011, 04:42:37 pmIt can become too expensive if you need to replace several custom ICs (assuming you can find them). If you are lucky enough to find a parts unit, a board swap often does the trick... assuming the parts unit has a working board for the swap.

author: Unknown
author_rank: Unknown
timestamp: December 20, 2011, 05:02:46 pm
content: If you're going to spend time and effort reparing an old piece of equipment, in my opinion it's much more satisfying to work on top quality equipment like HP and Tek, I wouldn't spend the same amount of time on a Telequipment scope, which was always produced cheap, inferior scopes compared to Tek (which owned them at some point). It's not like a used Tek scope is that more expensive than a used Telequipment scope these days. Tek and HP manuals tend to be excellent and easily available. Support (by hobbyists) is usually quite good in the TekScopes and hp_agilent Yahoo! groups.

author: don.r
author_rank: Frequent Contributor
timestamp: December 20, 2011, 05:08:38 pm
content: Yep. More value in rebuilding or repairing a Rolls Royce than a Chevette.

author: PStevenson
author_rank: Regular Contributor
timestamp: December 20, 2011, 06:05:08 pm
content: Quote from: alm on December 20, 2011, 05:02:46 pmI know what you mean and I would have scrapped it for parts but at some point this scope made it personal.at first it was totally dead but now there's the trace and so on but it's like the focus is drastically out so it's about half an inch thick.it's not like I spend hours slaving over it I just sometimes crack it out when it's raining and I'm bored.I've also got another scope that works perfectly except for the trace's drift upwards - it's a fully transistorized scope - there's not one IC to be seen !

author: FenderBender
author_rank: Super Contributor
timestamp: December 20, 2011, 10:55:17 pm
content: The 465M has one hybrid chip. In the picture, the scope was showing two traces...so I'd assume the hybrid is still working. If it's dead, it costs around $35...Which is a lot for a little chip, but still: The scope would only cost me a grand total of around $110, which is still considerably cheap. Other repairs would most likely be much less expensive. And you get a GOOD scope, not some piece of crap. I believe the 465M started at around $4,000 USD back in the day.

author: FenderBender
author_rank: Super Contributor
timestamp: December 21, 2011, 12:45:44 am
content: I think I might just buy the hybrid IC for the hell of it, because if it dies say in 5-10 years, there's a good chance I won't be able to find it..$40 here might save me a headache and some money down the line.What's the chance that mine is dead? The auction is ending in a day for the hybrid on eBay...Do they die frequently? I know it's used for the vertical preamp, which I can't discern whether the vertical works by looking at the picture which only had horizontal lines.

author: Unknown
author_rank: Unknown
timestamp: December 21, 2011, 01:42:45 am
content: In my opinion it doesn't make sense to spend $$$ on spare parts you don't currently need. I don't think the hybrid is known to have a high failure rate (check TekScopes to be sure), so who knows if that's the first to fail? Maybe some other part will die first, or maybe you'll replace/sell it before it dies. In the mean time, you've saved $40 that you can spend on something more useful.You bought this scope and immediately found a spare hybrid for sale, so it's not likely a rare item. Might as well buy it when you actually need it.

author: FenderBender
author_rank: Super Contributor
timestamp: December 21, 2011, 01:58:00 am
content: After considering it myself, it does seem silly to buy the chip. Solid state stuff usually doesn't die too often, but who knows since this was a unique Tek chip. I made a post on TekScopes. Hopefully the guys can help me.I have my fingers crossed that it works. If not, I'm going to be quite sad...

author: djsb
author_rank: Super Contributor
timestamp: December 24, 2011, 04:46:17 pm
content: I'm looking for a Tektronix digital scope to supplement my 2225. I've read on the yahoo group that the 2440 is the last model that is really repairable down to component level. This is because (according to the posts on there) the schematics on models after this one are no longer available in the service manuals. It is expected that if faulty the relevant PCB is replaced, impossible if they are no longer available.The 2440 has a 300MHz bandwidth and is usable up to 500Mhz. I'd like a digital scope so I can see non-repetitive signals and also observe RS232 comms etc.I'd love an Agilent MSO model but I can't stretch to £7K.Any thoughts.David.

author: don.r
author_rank: Frequent Contributor
timestamp: December 24, 2011, 04:52:52 pm
content: Quote from: djsb on December 24, 2011, 04:46:17 pmDo you need the bandwidth? Anything above 100MHz is not too useful for most situations but a storage scope is really handy many times. Why not plump for the Rigol 100MHz which is probably £300 now. With a new scope with warranty you don't have to worry too much about repairability (and for £300, no worries after warranty either).

author: Unknown
author_rank: Unknown
timestamp: December 24, 2011, 06:42:48 pm
content: Quote from: djsb on December 24, 2011, 04:46:17 pmSingle shot bandwidth will be much less than 300 MHz. In my opinion buying old analog scopes makes less sense than buying old digital scopes. The best analog scopes are no longer made and essentially the only analog scopes built today are cheaply made and much less powerful than eg. the Tek 2465 or 7000 series. Today's digital scopes are better than the old digital scopes in all aspects except may build quality. I would only buy an old digital scopes if I really needed one of the features (eg. a brand new DSO with 300 MHz will be fairly expensive) and could live with the limitiations (low sample rate/memory depth, sometimes slower, some of the early models had complex controls). Models from late 1990s or early 2000s have less limitations compared to the first few generations.

author: tom66
author_rank: Super Contributor
timestamp: December 29, 2011, 11:42:11 am
content: Quote from: PStevenson on December 20, 2011, 06:05:08 pmCheck this:http://www.cromwell-intl.com/radio/tek2445a.htmlFailed resistor in focus supply.

author: Gridstop
author_rank: Contributor
timestamp: December 31, 2011, 03:20:36 am
content: I was just gifted a Tek 7401 (1Ghz) with two 1Ghz vertical modules and 1Ghz timebase & 500Mhz timebase units. Pretty exciting! It's in really good shape, no broken knobs/etc, and everything seems to work great, with no burnout on the screen or anything. Unfortunately the 1Ghz inputs are 50 ohm, and no probes were included.So my plan is...Build one or two of the DIY 1Ghz resistive probes for probing CMOS/digital stuff with the 1Ghz vertical amps:http://koti.mbnet.fi/jahonen/Electronics/DIY%201k%20probe/Pick up one of the dual 200Mhz (7A26), 120Mhz (7A12), or 75Mhz (7A18) vertical modules on ebay. ($20-40) (1M 20~24pF input on most of them)Pick up two cheaper replacement probes from Rigol/Instek/Velleman/TPI ($25-50 ea, depending) Not sure what would be best.And then figure out how to calibrate the thing at least reasonably close. Vertical amplitude I can do because my DMM gives extremely accurate AC measurements and the internal calibrator looks spot on voltage-wise, but timebase I don't see how I can verify.One day I'd like to explore using a HD webcam or camcorder streaming to a PC to blow up the tiny ~4" screen and allow freeze frame, accumulation, and hopefully capture single-shot images.Of course, a good working 7401 with Ghz modules could fetch a few hundred on ebay, and buy me something like the GW-Instek 1072-AU... but I'm hesitant to give up this kind of speed and the ability to really image square waves in the 20-100Mhz range, which most affordable digital scopes ($<500) can't come close to doing.

author: tekfan
author_rank: Frequent Contributor
timestamp: December 31, 2011, 03:49:33 am
content: Quote from: Gridstop on December 31, 2011, 03:20:36 amNow that's a nice scope! Be careful with the beam intensity. You can easily burn the phosphor on the screen.There are two trimpots on the calibrator board. One for the frequency (R375) and one for amplitude. If you've got a frequency counter you can first try to tweak the frequency trimpot to bring the calibrator as close to 1kHz as possible. Then feed the signal to one of the channels and adjust the SWP CAL control on the time base (set at 0.1ms/div) to get exactly one cycle across the screen. The other ranges on the time base should still be pretty close to within calibration.

author: Gridstop
author_rank: Contributor
timestamp: December 31, 2011, 04:13:45 am
content: Yes, I did the trick with the intensity turned way down, move a flat trace below the screen, and then in a dark room turn the intensity up so you can see reflected 'glow'. The image is very smooth, with only some slight burn-in where the readouts are. When we first powered it up, I had no idea what a microchannel CRT was, and I kept trying to turn the intensity up, and it kept switching off on me, so I thought something was wrong with it and almost left it to be recycled! At least I know the limiter works properly. My understanding is that in addition to the CRT burning in due to the incredible electron output, the microchannel detector itself wears out cumulatively over time? I can't imagine using it more than a couple hours a week, and often not for months at a time, I'm just a hobbyist, so I don't think I'll have any problems.My main long-term concern is do I want to invest into this scope very much, and then have one of those irreplaceable hybrid IC things die on me... Not that $100 for a 2-ch vertical amp and some probes is a big 'investment'.As for the timing, the Hz counter on my DMM is accurate to 0.03% + 1 LSD so I should be able to dial it in to 1khz exactly. (or plenty close). But calibrating at 1khz really is close enough for say, 10Mhz, 100Mhz, or even 1Ghz? I figured I'd need some insane oscillator & long-period frequency counter to dial in those ranges...

author: tekfan
author_rank: Frequent Contributor
timestamp: December 31, 2011, 03:12:19 pm
content: I don't think the hybrids are much of a problem in these scopes. The Tek 2400 series seem to be the ones with the problematic hybrids. If you're in the US then you're lucky. You can get plugins and probes for next to nothing. It's not like this in Europe. People seem to realise the power of older well built instruments. A Tek 7104 goes for about 500 euros here.The time bases have air variable capacitors for the fastest ranges and trimpots for the slower ranges. If nobody touched them since the thing was last calibrated the sweep speeds should be fine.All that's really needed to adjust all the sweep speeds is a time mark generator:https://www.eevblog.com/forum/index.php?topic=5574.0

author: FenderBender
author_rank: Super Contributor
timestamp: January 01, 2012, 02:22:38 am
content: Hey I saw that Time Mark Gen a while ago. Cool piece of kit.My scope should be here either Monday or Tuesday. I have a little digital function generator. Can I do the calibration solely with a Function Generator?

author: tekfan
author_rank: Frequent Contributor
timestamp: January 01, 2012, 03:17:08 am
content: As long as you know the frequency, you can easily calibrate the slower ranges. If for example you have a 10MHz function generator, then the fastest sweep speed you can calibrate is 10ns/div. Since you need to see the whole cycle to accurately calibrate the sweep speed.Most oscilloscopes have several sweep speeds grouped to a single trimpot. You are relying on the accuracy of the resistors in the time base for the other time/div settings.

author: FenderBender
author_rank: Super Contributor
timestamp: January 01, 2012, 03:27:49 am
content: You would use Square wave I presume?My function generator can only do 5Mhz. Pretty pointless?

author: tekfan
author_rank: Frequent Contributor
timestamp: January 01, 2012, 04:15:38 am
content: You can use any waveshape but the square wave has the most defined edges making it easy to align it to the graticule markings.It's pretty pointless to try to calibrate a scope with a 5MHz function gen. Although you can still try and see if the various lower sweep speeds are still relatively accurate.Remember, a scope isn't made for precise frequency measurments. That's more the realm of frequency counters.I'm assuming you've got the Tek 465M. First check if there even is the need to calibrate it. If there isn't then just leave it alone.Dave made a nice video on how he calibrated his Tek 2225. That's really all you need to do for general use. Again using square waves for both frequency and amplitude adjustments is much easier than using sine waves.

author: FenderBender
author_rank: Super Contributor
timestamp: January 01, 2012, 05:40:12 am
content: Right right. I guess a scope is better for seeing how a waveform is affected by different factors. I did watch that video but I can't say I remember anything. To youtube...And this is my beloved function generator:http://www.ebay.com/itm/5MHz-DDS-Digital-Signal-Generator-Module-Sweep-Function-CPLD-STM32F103-/150725450410?pt=LH_DefaultDomain_0&hash=item2317efdaaa=/I didn't even realize at the time I bought it that I couldn't adjust the amplitude with this function generator...WTF is that? Grrr

author: Unknown
author_rank: Unknown
timestamp: January 01, 2012, 04:13:26 pm
content: Note that square waves don't necessarily have a duty cycle of 50%, so using anything less than a full period (eg. half a period) may introduce an error.

author: FenderBender
author_rank: Super Contributor
timestamp: January 01, 2012, 05:33:24 pm
content: I don't quite understand what you mean..