Agilent 34401A Self test -> display problem

[ThomasM]

Hello everyone,
I own a (preowned) Agilent 34401A, which I purchased recently. The unit is working well inside the specs. I had it checked in the calibration department of the company I work for. But there is one issue which bugs me. When I hold the shift key, while I turn on the device (self test) the display stays dark. In normal operation the display is working fine.

Does anyone have a clue, what could be the problem? I appreciate all inputs.

Regards
Thomas

[Hornethandler]

Thomas

Does it pass the “complete self-test”?

Perform a complete self-test.
The complete self-test performs a more extensive series of tests than
those performed at power-on. Hold down Shift as you press the
Power switch to turn on the multimeter; hold down the key for more
than 5 seconds. The self-test will begin when you release the key.
If the self-test is successful, “PASS” is displayed. If the self-test is
not successful, “FAIL” is displayed and the ERROR annunciator turns on.

[charlyd]

 Pictures?

[ThomasM]

Hello Hornethandler,
I actually do not know what the result of the complete self-test is, because of the display.

I hold the shift key, switch on the device, waited five seconds (all segments of the display are illuminated), than release the shift key. Now the self-test begins (I can hear some relais switching) an in the same instance the display turns dark. I waited, but the display stays off. Only thing, when I press the again, the indication for shift is illuminated.

So I do think, that the self-test is performed, but I can't see what the results are.

I have taken a short video to show the behavior: https://www.dropbox.com/s/gwce7g8ewlaf01c/9262215f-301a-420d-b361-22ff28ddf32e.MP4?dl=0

Thomas

[Hornethandler]

Thomas,

I’m afraid I don’t have much experience with faults in this meter; I wish I could be more helpful.

Do you have the service manual?
Here’s a link.  https://www.keysight.com/upload/cmc_upload/All/34401-90013-mla2.pdf

I gave the manual a brief look and it seems quite comprehensive.  I’ll look it over again for something specific to your symptoms and will let you know if I find anything interesting.

Good luck, Thomas; looking forward to finding the problem.

[ThomasM]

No problem, I appreciate your link to the manual.

For me, it looks like a rather mysterious problem. But I will have a look into the manual. Who knows, maybe I'm lucky.

[Hornethandler]

Thomas,
Just saw this in the manual; it may be a starting point.

Agilent 34401A Multimeter
Chapter 6 Service
Self-Test Procedures
Pg. 102, Test 601

Front panel does not respond
The main CPU U500 attempts to
establish serial communications with the front panel processor U600.
During this test, U600 turns on all display segments. Communication
must function in both directions for this test to pass.

[ThomasM]

I found out, that when I initiate the self test from the menu, the display works fine. I can see the "Testing..." with an final PASS.

I'm curious, if the original problem is firmware related.

Thomas