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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: May Tue 26, 2015 8:06 am 
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Joined: May Tue 26, 2015 5:47 am
Posts: 4
Hi,

I have been fixing TDS-420 (no suffix letter) scopes for myself and a few fellow die hard Tektronix scope people for a few years now. Not an easy task without even the most basic schematics as reference. So what I have been tinkering with on and off is making my own schematics of critical areas in the 672-1476-04/xx board. I kept hitting walls though when I got near the several large ASIC chips where I basically have to make guesses.

I spent quite a bit of time asking Tektronix for schematics relating to this model scope and they told me they have purged everything they had on these scopes and the documentation no longer exists, but they have given me tacit permission to ask around and see what I can find. Basically what they told me is they could care less about these scopes and do no care what I do with them.

It is my intention to continue with my reverse engineering of the scope to create enough of a schematic to be useful to people like me who own and use these on a daily basis.

So what I would like to find out is if anyone has ANYTHING on these scopes including partial schematics, calibration software, or identification/datasheets on the large chips in these machines. FYI: The schematics I am creating are being captured in ORCAD.


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: May Tue 26, 2015 9:18 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2090
Location: Weimar, Texas
Service Manual (not as detailed as I had hoped) but it's all over the web. No schematic though... makes me wonder if there ever was one

https://www.i3detroit.org/wi/images/0/0 ... Manual.pdf

ElectroTanya

http://elektrotanya.com/tektronix_tds41 ... nload.html

KO4BB's manuals including the programmers manual

http://www.ko4bb.com/manuals/index.php? ... _-_TDS-420

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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: May Wed 27, 2015 2:01 am 
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Joined: May Tue 26, 2015 5:47 am
Posts: 4
Hi,

The only TDS service manual that actually had a real schematic is the "B" model. In my talks with a high honcho at Tektronix, I was told that the B model schematic was created for one specific customer who required it to make a large purchase (anyone besides me care to bet that the mysterious unnamed power-buyer was some branch of the United States Department of Defense? :)

I was told that "B" service manual with an honest-to-God component level schematic was never intended for public distribution, and reading between the lines I gather Tek was none too happy it escaped to freedom. The "B" version is close enough to the no-suffix and "A" suffix models to ONLY show the design methodology of the general TDS product line architecture, but the "B" schematics are nearly useless to buzz no-suffix or "A" units to the component level for repair.

I have been specifically told, and I do believe it to be true, that there was never a release of the component level schematics of the other model units. And also, I was specifically told that all old service data was deliberately scrubbed from the archives as useless. Since every company I have ever worked for kept design records forever, this is something I am less than ready to accept at face value.

Being a design engineer myself I would bet a years salary that some of the engineers who developed the TDS line kept personal copies of the schematics and notes, but without being able to identify, locate, and talk to some of these engineers I would not know where to start the hunt. I was told by a former Tektronix employee that the chief engineer on the TDS project was deceased, but I was never given his name, or the name of anyone else who was on the project. Since the model scope is only 25 years old you know that most of the individuals involved are still around somewhere (and might be still at Tektronix), but without an insider contact it is a dead end. I know I would love to get in contact with any who are around if I could!!!!!!

Back to the basic subject. What I am in the process of doing, is attempting to create a component level schematic of the 420 (no suffix) model (at least the analog board portion to start with) based on the reference half dozen or so units I have in stock in various states of repair. I know that what I am attempting will be somewhat limited in scope (pun intended), but with something this complex, I have a godawful time chasing down bugs in the dark.

I have several revision boards which to my naked eye are identical, so I am hoping that a component level schematic, in conjunction with the officially released service documentation, will make fixing these things more productive and less like torture. It helps that I own a surface mount rework station and can remove and replace all surface mount parts repeatedly without damaging components or lifting traces off the boards.

There is relatively little electronics in the no-suffix scopes that can not be bought off the self from Digikey or Mouser so with some real documentation we could keep these useful machines around for a long long time.

Stephen


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: May Wed 27, 2015 3:30 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1063
Location: Tucson AZ
Stephen,

I don't know what to think about why the TDS 4xx series scopes and the "secrecy" of the schematics and service info.

Seems quite ridiculous to me, but if my 460 takes a hard dive, it'll most likely end up seeing some lead poisoning from an 8mm.


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: May Wed 27, 2015 4:24 am 
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Joined: May Tue 26, 2015 5:47 am
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As to the secrecy involved it appears to be an integral part of the Tektronix culture in the modern era. They do not WANT anyone to know how they do things. It is probably an attempt to protect their (rightful) intellectual property, which is silly of course.

I can guarantee that from a cold standing start, an AVERAGE team of Chinese/Korean/Japanese/Russian/American/you-name-the-country engineers could disassemble a TDS-420 scope and have full component level schematics and flow charts in less than one week. In two weeks after that they could have fully reverse engineered the firmware and rewritten and improved upon it.

Part of this may just be simple economics. They are in business and want you to buy new scopes as much as possible. And as it is intuitively obvious that there are a lot of us out here with very tight budgets who need to use what we have as long as possible and this does not make them money.

We must as our only option, repair/service stuff ourselves. So you break the cal sticker. Re-calibrating an old scope is quick and cheap, repairing it is slow and expensive.

It is one of the many reasons HP/Agilent dominates the scope market - and for the most part owns it now. HP would always give you component level documentation if you ask for it along with full component specs and factory part numbers. In new stuff with super high level integrated circuitry it may not be much help but they will give it (or sell it) to you. I have DVD's with hundreds of HP service manuals with full schematics, at least a couple of them old enough that they were hand drawn.

Tektronix stopped doing that before the TDS series scopes were birthed.

Do not get me wrong. Tektronix makes some killer equipment, but If I am in charge of buying test gear for a small to medium size company today, I am more likely to purchase equipment upon which I can perform minor repairs in an emergency. The idea of being down for weeks twiddling my thumbs does not thrill me.

Stephen


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: May Wed 27, 2015 4:30 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1063
Location: Tucson AZ
TekJunkie wrote:

Do not get me wrong. Tektronix makes some killer equipment, but If I am in charge of buying test gear for a small to medium size company today, I am more likely to purchase equipment upon which I can perform minor repairs in an emergency. The idea of being down for weeks twiddling my thumbs does not thrill me.

Stephen


Absolutely agree.

We've got an old HP network analyzer at work that has gone done. It's the only one they have...... :roll:

They don't know if they can get it fixed, but at one time, there were spares until management thought spares weren't needed.

In any case, that network analyzer was discontinued in '76.

Still repairable though, unlike the new PNA's running Windows XP that are floating around that are less than 10 years old and literally have no support for them.


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: May Wed 27, 2015 5:05 am 
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Joined: May Tue 26, 2015 5:47 am
Posts: 4
I have multiple Spectrum analyzers (HP), a Network analyzer (HP), a frequency standard, and more signal generators and ARBS than you can shake a stick at, along with programmable power supplies (HP, Tek, & off brands), 4 freq counters (HP), 3 living and 6 dead (in repair mode) Tek scopes. Maybe a hundred Tek probes of one kind or another (some quite exotic).

I have detailed service info on almost everything except the Tektronix scopes.

Truthfully, I would probably be better off just dropping them on my foot, rather than attempting repair of either of the Harry Potter magical boat anchors bearing the enchanted names HP Network Analyzer and HP Spectrum analyzer, but honestly I still get the warm fuzzies just knowing I have schematics in hand should the need arise.

Stephen


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jun Wed 24, 2015 6:56 pm 
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Joined: Jun Wed 24, 2015 6:22 pm
Posts: 1
Hello @all,

many thanks for this thread!
I own a TDS420 also and I have to fix all the capacitors, but there are some damaged electronic parts, I can't identify them any more. Can anybody help me to identify this parts, please? I'll try to add a foto here (I have to wait 24h because of new member).
Many thanks!

Greetings Ren :D


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jun Wed 24, 2015 9:41 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2219
Location: Seattle, WA, USA
Sure. I can try. Contact me through my site at www.dasarodesigns.com.

-Matthew

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If it ain't broken, you’re not trying hard enough...


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jun Thu 25, 2015 9:50 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2219
Location: Seattle, WA, USA
For the benefit of others here is a link to a picture showing the damaged components with their correct replacements noted.

http://www.dasarodesigns.com/~medasaro/TDS420%20Front%20Panel.jpg

-Matthew

_________________
If it ain't broken, you’re not trying hard enough...


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Apr Fri 28, 2017 7:33 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 374
I've just been working on a TDS460, and I found this thread when I was looking for information on the errors. It's working now, after repairing numerous open traces.

I ended up doing a continuity check on every connection in the areas with visible corrosion. I found the most trouble was where a trace connected to a PCB pad under a cap or resistor.

I also found that the leakage problem isn't limited to SMD caps. Almost all of the through hole caps in the power supply were leaking badly. The leakage was hidden under the caps, and almost impossible to see without removing them.


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jun Mon 19, 2017 7:35 pm 
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Joined: Jun Mon 19, 2017 7:26 pm
Posts: 8
I bought a 420 on Ebay from a guy In Thetford Mines, Canada (Old Asbestos Mining town). It showed a startup fail, can't remember now which one, but found this thread, ordered all the caps, replaced all the caps (and one fried small 100nf one). There were no burned traces, so I just put it back together this morning, and success! It works perfectly. Thank you, Mathew, for the info on how to get it working again.


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jun Mon 26, 2017 5:55 am 
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Joined: Jun Mon 19, 2017 7:26 pm
Posts: 8
Well, it was working 100%, now these errors.


Attachments:
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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jun Mon 26, 2017 4:32 pm 
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Joined: Jul Wed 08, 2009 12:17 am
Posts: 928
Location: Wyoming, Michigan
I could use some advice on one too.
viewtopic.php?f=8&t=323442


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jun Wed 28, 2017 11:40 pm 
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Joined: Jun Mon 19, 2017 7:26 pm
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found two more SMD caps hidden under a ribbon connector on the attenuation board, but still have errors...


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jul Sat 01, 2017 2:21 am 
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Joined: Jun Mon 19, 2017 7:26 pm
Posts: 8
Reflowed some dark/questionable contact pads on a couple ICs and some other components, removed a couple possible solder bridges, checked the continuity on all my replaceed SMD caps, and seem to have fixed the errors, Though I'm not 100% sure my trigger is working correctly.
Progress, anyway.


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jul Sat 01, 2017 2:11 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 8198
Location: Sunbury, Ohio 43074
imho, and based on a long career in test instruments and broadcast equipment, I believe that Tektronix and MANY others don't want their schematics and service literature out there for three reasons. (1) They don't believe anyone other than "the factory" are qualified to service them (likely true, since they keep everything secret LOL ) ... (2) They want instruments and equipment to go "obsolete" so at some point you have to buy a new one and (3) They are protecting their own income stream in servicing their own instruments. All of these are, of course, legitimate "business" concepts, but it is very frustrating to people that live in the real world and cannot buy a new instrument every few years. I had a TEK 520A vectorscope, in which the crystal oven went out. Therefore, no more precision internal frequency reference. Tek told me the parts were "no longer available, just buy a new instrument". Ok, no problem, $10,000. I fixed it myself at the time ... had to wind a new heater coil out of parts found around the home.

Tektronix and HP seemingly pioneered the use of "factory only components" that were not available from generec replacement parts distributors. I remember back in the day having to order "house number" transistors for something as simple as a 528 waveform monitor. It was only much later that myself and others like me figured out generic replacements for some of these components, just in time for such knowledge to be rendered useless by the next model of instrument :) .. it's a kind of vicious circle.

Just my 2c .. the scope of this topic is immense :-D (yea, I know lol)

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https://www.bbtvtestequipment.com


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jul Mon 03, 2017 5:53 am 
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Joined: Jun Mon 19, 2017 7:26 pm
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So I did another Signal Path Compensation, and am back to 100% serviceable. I think that when I did a SPC while the caps, etc were not good, It drove the SPC to the limits, and wouldn't trigger at all, but now it is all in working order!


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jul Thu 13, 2017 9:52 am 
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Joined: Nov Tue 15, 2016 10:42 pm
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Hello

Is it possible to use tantalum capacitors instead of electrolytic ones. Pro and cons?

Thank you


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 Post subject: Re: Some hints on Fixing Tektronix TDS-420 Oscilloscopes
PostPosted: Jul Fri 14, 2017 12:50 am 
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Joined: Nov Wed 30, 2016 7:35 pm
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Location: Sunbury, Ohio 43074
My "non engineering" opinion on this ... because a dissertation would be very wordy ....I generally don't think twice using a tantalum if I don't have the proper electrolytic on hand, especially in small signal and lower voltage circuits. Also in low voltage power supply filtering in some cases. But you also have to keep an eye on the specs of the replacement you want to use vs the one you are replacing. Tantalums are generally superior to electrolytics, but at a higher cost. Tantalums do not like high heat either and fail in circuits that may cause them to heat. Also, in higher voltage applications, you are likely to get into very expensive tantalums. In those cases you are probably better off with an electrolytic. New ones are significantly smaller than the days of old, for the same or better performance.

So, basically, "it depends" but for small signal and low power, if cost is no object, I'd go with a tantalum. Then again, I've known a lot more tantalums to short dead, than electrolytics .. but hell, we're not going to outlive the equipment we are re-capping are we :)

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Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


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