Comments on: Tektronix 2440 Oscilloscope Repaired- Part 4

By: Kurt Moser

Kurt Moser — Wed, 26 Apr 2023 07:52:32 +0000

Hey Albert,
According to Your 4-part series where You show the repairing of a Tek 2440, it seems
that You are a specialist of this scope. My 2440 shows a very strange effect.
It is to mention, that no of the built-in tests fails; everything seems to be ok !
But the scope beahves like it had only a sample rate of 250 MS/s.

The picture which I uploaded here to the Dropbox
https://www.dropbox.com/s/ud9l484lbxabmkp/20230417_132059.jpg?dl=0
was taken with the following settings:
Acquisition: Envelope Trig Mode: Singe seq. Trig. Pos: 1/2
The input signal was a 20 MHz sinusoidal waveform with 1.2 Vpp amplitude.
One can cleary see, that the A/D-converters change its output after 4ns but
at the same time.
My question is: Do you have an idea of what is going on here ?
What would you suggest to do ?

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By: Albert van Bemmelen

Albert van Bemmelen — Fri, 17 Dec 2021 12:28:48 +0000

And in case your 2440 or 2430 scope doesn't startup, behaves erratic, or simply freezes in the middle of a measurement, it also may be caused by bad capacitors. Which means its time to replace the old capacitors on those board(s). In that case checking following link may be useful: https://www.eevblog.com/forum/repair/tektronix-2432a-repair/

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By: Albert van Bemmelen

Albert van Bemmelen — Tue, 12 Oct 2021 07:09:25 +0000

Update 12-november-2021: Yesterday I now also fully calibrated my Tektronix 2440 scope externally!

And I also first upgraded my oscilloscope by replacing both old battery backupped 32k SRAMs U664 and U350 by FerroMagnetic FM1808 DIP 28pin chips. Because without the calibration data in these chips the scope won't work, no working screen, no nothing, so I also used the uploaded firmware bin files from this great guy - see following link - to keep my 2440 alive after replacing both SRAMs. And pre-programmed my FM1808 with them so my scope would still work to be able to calibrated it again afterwards! Those bin files (from an almost identical 2430 oscilloscope) can be found here: https://www.diyaudio.com/forums/equipment-and-tools/312894-tektronix-2430a-lost-cal-data-repair.html . And if you have a dead 2440 most likely these SRAMs lost there original firmware and need to be restored first! PS: I used my even almost as old SYSTRON 100A Pulse Generator to finish the last external CTE calibration check. And I now have a fully Internally (Selftest) and externally calibrated Tektronix 2440 oscilloscope. Also the above given link provides the easy Calibration steps you can follow. And in Part7 of this Youtube video you can see how to setup the signal for the final CTE calibration step: https://www.youtube.com/watch?v=lvCRK7JbcYs

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By: Albert van Bemmelen

Albert van Bemmelen — Mon, 10 Dec 2018 11:47:37 +0000

Oops: I noticed you mentioned 2 scopes of which only the 2440 needed fixing and not the 2430A that was still fully working. In this case my advice still would be to start with checking the flow diagrams in the servicemanual. The manual for our 2440 is downloadable here (much smaller in size than the 2430 manual which is a large 153MB!): https://www.tek.com/manual/2440-service-manual
I hope you also still are able to find any replacement parts like I did with the A/D converters I needed for my 2440 repair. My warm regards from the Netherlands. - Albert (;).

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By: Albert van Bemmelen

Albert van Bemmelen — Mon, 10 Dec 2018 11:33:43 +0000

Hi Thomas. Sorry for my late reply. I do not check upon my older articles to see if someone had posted any new questions. And I do not think that many of us do.
But to answer your question, I think that most likely at least one of your Tektronix complex mainboard chips must be failing. In my 2440 repair it was a A/D converter chip that caused the internal main power supply to blow. And it shorted out the AC 230V input voltage and blew a fuse and the diode bridge rectifier to kingdom come. In my 2440 Tek like in yours there are quite a lot of those complex dedicated chips placed on the mainboard(s) and I was lucky to easily find those complete service manuals for my scopes. And if you need yours for your 2430 scope you'll find it here: https://www.tek.com/manual/2430-service-manual. I think the best thing you can do is to follow the structured flowcoded service diagrams in your manual and start with the easy to check tests. Without it servicing such a complex device is a bad idea. I never opened a 2430A before so I can't point out anything that would be of any help. But in case you have the money and the time, sometimes you may be able to find a complete working second hand used board or an identical scope not working with spare parts on eBay you could use. Good luck with fixing your 2430A scope!

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By: Thomas Niedermeyer

Thomas Niedermeyer — Fri, 24 Mar 2017 18:46:34 +0000

Interesting and instructive article, Albert. I recently acquired a fully functional 2430A with very few hours on it and a non-functioning 2440 that was thrown in with the deal. The LV power supply in it is working and putting out the correct voltages, but the scope never fully comes to life. There is no trace, although I'm pretty sure the HV supply works because there are some light flashes on the screen when I turn the unit off. The power-up comes to a halt with all 3 GPIB lights on and the second and third of the five trigger lights lit. I have full documentation for both units. Any ideas or recommendations would be appreciated. Warm regards from Austria. - Thomas

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By: Paris Azis

Paris Azis — Wed, 14 Oct 2015 12:59:03 +0000

In reply to Albert van Bemmelen.

This is what most people call “learning by doing” Albert.
And interpreting it sequentially backwards up, “you did it, you learned it and you have written it”. Plus, you did it good!

Greetings

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By: Albert van Bemmelen

Albert van Bemmelen — Wed, 14 Oct 2015 06:50:34 +0000

In reply to Paris Azis.

Thank you dear Paris. I appreciate your kind comments very much. But I probably wouldn't search as far as the Magical World you're painting. It is after all only a bit of Science without the Fiction. Maybe in the not so distant future it also will be possible to shave without having to shave yourself. Because that is a thing I do not want to waste time on since it just keeps on growing whatever I do. About this Tektronix repair I just didn't knew I was able to do an article on these quite expensive and above all Magical designed Tektronix devices until my friend brought this 2440 Oscilloscope to me for repair.

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By: Paris Azis

Paris Azis — Tue, 13 Oct 2015 07:10:37 +0000

Hey Albert

I fully understand now, upon completion of reading this last article of yours, the reason that you forgot to shave yourself and your beard appears as noticeably grown…What an amazing “digital thirst” is the one you have man!
Well, keep on coding, decoding, multiplexing and demultiplexing, searching for glitches in your digital signals, but remember! All of it exists only in order to represent in the highest possible accuracy the really magic world we live in. The world of the analog signals which the entire Mother Nature provides and works with…

Thanks again for your effort.

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By: Albert van Bemmelen

Albert van Bemmelen — Sun, 11 Oct 2015 09:58:33 +0000

In reply to Anthony.

Thanks Anthony! I'm very pleased with the perfect results too!

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