Agilent 34401A spontaneously mode change to Ohm measurement.

[Fedor]

Hello, please help to repair the problem I finally caught on camera.
It spontaneously changes mode to Ohm measurement.
I resoldered already a couple of IC, but it did not help.
What to check? Where to look?
Sorry for my bad English



Hi Dave and all the EEVBlog viewers!

[DaJMasta]

Have you checked the front panel and the cable connecting to the main board?  Could be gunk in the switch, some sort of error in the keyboard reader micro, or even just a loose contact coming over to the main board.

Do you have it connected to GPIB or anything?  Could there be another device issuing it commands?

[Fedor]

Have you checked the front panel and the cable connecting to the main board?  Yes, I checked

Could be gunk in the switch, some sort of error in the keyboard reader micro, or even just a loose contact coming over to the main board. It looks like no gunk, it looks like reboots (all digits on) when I
push the 2W button, no reload.

Do you have it connected to GPIB or anything?  Could there be another device issuing it commands? This problem appears without GPIB... nothing connected.

[wictor]

It seems to be rebooting. Have you checked front panel tantalums?

[mimmus78]

It seems to be rebooting. Have you checked front panel tantalums?

Yes it seems front panel is rebooting ...

Inviato dal mio ONEPLUS A5010 utilizzando Tapatalk

[HighVoltage]

You could disconnect the front panel ribbon cable and use remote control over GPIB or RS232 and see if the DMM behaves correctly  and proof that the problem is in the front panel only.

[Fedor]

You could disconnect the front panel ribbon cable and use remote control over GPIB or RS232 and see if the DMM behaves correctly  and proof that the problem is in the front panel only.

I like your advice!!!
And according this, I took a front panel from second unit!  And First front panel connected to second unit... Result: Second unit work well with first front panel, But first unit NO, the problem still exist on the first unit. So:
Front panel absolutely good, front panel Connection good as well (I clean and checked it well enough). And problem does not appear when I touch front panel flat cable.
Seems problem somewhere on the board.

[coromonadalix]

As usual   check all supply lines,  i changed  all the caps and tantalums in my units to e safe,  i had the yellow ones,  they had a darkish color spot in the center

[Fedor]

1 Year Later I still use it, and did not solve the problem.
Yes I checked all power lines, all caps looks nice and even replaced relay #102 on the mainboard.
Do someone new users have an idea?)
Still want to fix it.

[Zucca]

I have to ask: self test everything ok?

Still do what HighVoltage suggested, it will give you some suggestion to what to check.

[coromonadalix]

Had similar problems with an third  34401a, i've bought for fun, intermittant display all supply lines where good

The flat ribbon front panel connector, was not closing well (kinda stayed pushed a little) on the wires ....  played with it a few times ... and re-inserted the wire and worked fine afterwards, maybe the previous owner had a go in it ?

Not sure its related to your problem(s)