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TDS540 startup vs diagnostic tests

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StefanS
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Joined: September 29th, 2021, 5:26 pm
Country: United States

TDS540 startup vs diagnostic tests

Post by StefanS » September 29th, 2021, 5:40 pm

Hi Everyone,

I’ve just finished recapping a TDS540 and continue to see errors at startup:

FAIL ++ Acq/Proc Interface
FAIL ++ Acquisition

However, if I immediately run diagnostics from the utilities, the unit passes all tests, including SPC. The log shows two previous sram errors at addresses 0x7300000 and 0x7320000 that appear to have cleared since I cleaned around U101 on the acquisition board.

Any thoughts or solutions?

Thanks,
Stefan

strick
Posts: 305
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by strick » September 30th, 2021, 7:06 am

StefanS,
the error log should show a longer message about the ACQ fails. If it happens on startup, but not when you run the later full tests, then I would suspect you are getting a TI-1 or TI-2 fail.

I have at least two scopes that do that... It's really hard to troubleshoot because it "just goes away" after start. Since these are test scopes, I don't worry about it.

If you have a serial debug port, you can see the failure happen on real time on bootup. If you don't have the serial port, you should probably build one, if you have an option 13 card.

If you don't have the card, I can probably send you one.

Strick

StefanS
Posts: 8
Joined: September 29th, 2021, 5:26 pm
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by StefanS » September 30th, 2021, 8:40 am

Hi Strick,

Thanks for the reply. I just got a GPID to USB interface and was able to clear the log. Restarted the unit 5x and got no errors on startup. Sixth time, the errors reappeared and the log showed the SRAM errors again. U101 definitely has corrosion on one side from a leaky cap. Could that be the cause of the startup errors? Can’t figure why it’s intermittent, though.

Is there a listing of GPID commands so I can run the diagnostics from my PC?

Best,
Stefan

strick
Posts: 305
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by strick » September 30th, 2021, 11:46 am

The Tek programmer manual lists the commands you can send. Just search for it on the net or it the Tek website.

you can use IBIC (found in the GPIB directory) to start a manual session, or you can address the scope with the gpib addressing utility in windows.

I've never seen memory faults that clear themselves, but then again, I'm sure it's possible.

Strick

StefanS
Posts: 8
Joined: September 29th, 2021, 5:26 pm
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by StefanS » September 30th, 2021, 12:23 pm

Hi Strick,

Let me be as precise as possible about what I am seeing:

I can turn on the scope multiple times, sometimes passing sometimes failing with:
FAIL ++ Acq/Proc Interface
FAIL ++ Acquisition

In the log, I get the following:
ERROR: diagnostic test failure
acqMemAddr. ** addr = 0x7300000 exp data = 0x101 actua...
ERROR: diagnostic test failure
acqmemAddr. ** addr = 0x7320000 exp data = 0x5555 actu...

If I clear the log and successfully run the diagnostics, no messages appear in the log. However, if on a restart the fails occur, the two messages in the log reappear.

strick
Posts: 305
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by strick » September 30th, 2021, 2:13 pm

StefanS,
that's normal. The log only get's written with errors and occasionally when connecting to a GPIB source.

Your error indicates that you have a memory fault in channel 1, in the first two memory chips (by chip number, e.g. 401 and 402). Now, you could also have memory errors after that, but they will never show until you get past those two chips.

Now, only one chip could be bad, but the error is specified in a word-sized package, so you can't tell which chip it is. Occasionally, I have had ACQ memory faults after replacing the surface mounted capacitors with regular low ESR caps. I recommend you remove the four caps associated with channel 1 and remove all solder from the pads and around the pads and see if the error goes away.

If it does not, you are in to memory chip replacement. These can be REAL hard to find, especially if they are not SOP type chips.

Strick

StefanS
Posts: 8
Joined: September 29th, 2021, 5:26 pm
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by StefanS » September 30th, 2021, 5:32 pm

So you are suggesting I remove the 4 caps and test the scope without them? Just want to be sure. Are they just filter caps?

-S

strick
Posts: 305
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by strick » October 1st, 2021, 8:38 am

Yes,
When I first started fixing these scopes, I used to think it mattered. It doesn't. They are just there to help prevent unwanted surges in the supply to the circuit. It will still work just fine under nominal conditions.

When I test an ACQ board, especially after leakage (and scrubbing with Simple Green with a Toothbrush, washing and drying in the Sun), I'll give a check to see if the errors have cleared before soldering new low-ESR caps.

When I did this and found the board clear of errors without caps that suddenly threw a memory error, I realized that I had caused it. I removed the caps (and solder) and tested and Voila!, no errors. Carefully soldering on the caps and the board was good. While I could never see where my soldering had problems, it just worked.

However, If removing the caps and solder does not work, then you are in the memory replace game...

Strick

StefanS
Posts: 8
Joined: September 29th, 2021, 5:26 pm
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by StefanS » October 12th, 2021, 9:16 am

Hi Strick,

Finally got around to removing the four caps on the channel one SRAM. It appears to have improved, but one in twenty boots still gave me the same errors. So, two questions: first, should I replace the caps or leave them off? Second, is it possible that NOT having the caps could result in intermittent errors, too? You sort of suggested this in your last response.

Thanks for your help!
-Stefan

strick
Posts: 305
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by strick » October 12th, 2021, 9:56 am

Sure. You might be getting more voltage spikes on the chips without them. I would just replace them with regular radial low-esr caps. Just be careful with the soldering job.

If you keep getting the rando memory failures and it doesn't affect the display, you might just ignore it.

Strick

StefanS
Posts: 8
Joined: September 29th, 2021, 5:26 pm
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by StefanS » October 17th, 2021, 12:07 pm

Hi Strick,

Just wanted to round up the thread: the caps have been reinstalled, error logs cleared, and I've had about 30 boots with no errors. Thanks so much for your advice and patience.

-S

strick
Posts: 305
Joined: March 22nd, 2016, 11:23 am
Country: United States

Re: TDS540 startup vs diagnostic tests

Post by strick » October 17th, 2021, 5:31 pm

Great! That's good news! Enjoy...

:D Strick

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