Tek TDS 420 self test says "Fail ++ Acq" what is that?

Posted in the Tektronix Forum

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1 - 13 of 13 Comments Last updated Jul 30, 2013
Tom

Chino Hills, CA

#1 May 7, 2007
Anyone know what that error is, and how to make it not appear?

This scope works great, even when the error shows on start-up, which is about half the time. I would just like to make the error go away so I can sell it better on ebay, or at least state what it means.

Anyone know? Thanks!~Tom
John

Ireland

#2 May 8, 2007
Hello Tom,
Its been a couple of years since I've used one but you could try running a Signal Compensation Test (I forget exactly what its called) It compensates for temperature drifts and mostly effects the millivolt ranges. let the scope warm up for 20 minutes before running the test and switch of any other electrical equipment nearby which might cause interference. You should find it in the self test menu.
Good luck,
John
Tom

Chino Hills, CA

#3 May 9, 2007
Excellent, thank you! I have a feeling you are correct. Will try this weekend and let you know.~Tom
Tom

Chino Hills, CA

#4 May 12, 2007
It didnt work! Same error, half the time. Here is an answer I got from a seller on ebay:

"There is about 30 electrolytic caps on the acquision board. Chances are thay they have dried out due to heat and age. Alot of times, it causes the regulators to oscillate. May not be the problem though. If you go to the Tek web site, you can get a service manual for the TDS-420. In any case, I would guess it's either on the acquisition board or the attenuator board. The 420 and the 460 are terrible about that particular failure. Hope this helps."
Volkan

Castro Valley, CA

#5 Aug 22, 2007
I've TDS 420 and I want to clear previous error log. I couldn't find any info about it. Is there any way to do it?
Thanks,
Volkan
RLevi

Marl, Germany

#6 Sep 28, 2007
I got a TDS460 with same mssage problem of faulty acq unit.
found a burned IC U138 at the bottom of the acq board (fan side). The IC mark can't be read anymore. Can someone check what is the name of this IC?
glenn

Carnegie, Australia

#7 Jun 3, 2008
Replace EVERY elctro cap on all PCB's especially the the Acq and Atten boards.(both on bottom) Then THOUROGHLY clean the pcb in particular around those caps. You will most likely see residue from the caps and even blackening of some IC leads. Make sure all that is removed also. Then, it will probably work fine. Mine did. June 2008 Glenn
RLevi wrote:
I got a TDS460 with same mssage problem of faulty acq unit.
found a burned IC U138 at the bottom of the acq board (fan side). The IC mark can't be read anymore. Can someone check what is the name of this IC?
Harry

Linkenheim-hochstetten, Germany

#8 Jul 8, 2008
Hi Glenn,
I have exactly the same problem, but each electro cap looks fine. I have a burned IC U138 on the Acq Board, but I can't read the label. It supposed to be a TL074C OP but I'm not sure. Watch these Pics:
http://forum.iwenzo.de/sonstige-reparaturtipp...
Should I change the caps anyways? At first I will solder in a TL074. Hopefully it works.....
Harry
glenn wrote:
Replace EVERY elctro cap on all PCB's especially the the Acq and Atten boards.(both on bottom) Then THOUROGHLY clean the pcb in particular around those caps. You will most likely see residue from the caps and even blackening of some IC leads. Make sure all that is removed also. Then, it will probably work fine. Mine did. June 2008 Glenn
<quoted text>
Ken Feldhaus

Cincinnati, OH

#9 Dec 28, 2008
I have a TDS420. It sat for years before I tried to power it up. I passes all tests but it says TEK Running:OFF. How can I get it in the running mode?
Teodoru

Cristesti, Romania

#10 Feb 22, 2009
Ken Feldhaus wrote:
I have a TDS420. It sat for years before I tried to power it up. I passes all tests but it says TEK Running:OFF. How can I get it in the running mode?
Hi Ken, I have a TDS420, also with same message...! Have you fixed the fault? How? Thanks, Teodoru
Ken Feldhaus

Cincinnati, OH

#11 Jan 30, 2010
Teodoru wrote:
<quoted text>
Hi Ken, I have a TDS420, also with same message...! Have you fixed the fault? How? Thanks, Teodoru
Teodoru Sorry for the long wait I have been away for awhile. Anyway I have not fixed it and if you have couls you send to me the answere
Thanks
Blake Reed

Durango, CO

#12 Jun 10, 2010
Thanks for the info on the caps.

I have a TDS644a that had the Acc error. I replaced all the capacitors but the scope still had the errors. I found that the board must be thoroughly cleaned. Leakage from the caps got under the op-amps and had enough conduction to cause errors in the signals. I bathed the board in alcohol, scrubbed with a toothbrush, and then rinsed and scrubbed with water. Set it in the sun to dry, ran a re-cal, and it works perfectly!
Al Royce

Wilmington, CA

#13 Jul 30, 2013
Tds 460a fan runs as soon as u switch the switch on the back.
Scope has 2bad pcb s but that is not causing the fan to run.

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