Freezing Agilent 34401A [Solved]

[zed65]

Hi, I got this weird fault on my 34401A, sometimes it just makes a beep and stops responding to any button and the display freezes.
Seems like it enters some kind of sleep-mode and refuse to wake up again
The problem happens rather random, sometimes just after a minute and sometimes after an hour.

Do you have any suggestion? Where do i start?

/Alex

[stmdude]

Does it happen in all measurement modes?

What does self-test say?   (Hold shift while powering on, release after a few seconds)

What kind of signals are you measuring when it's happening? Does it happen with other signals? (AC vs DC, ranges, etc)

[zed65]

It happen on all modes, when measure or nothing connected to the terminals (totally random).
No error on selftest.

[Kleinstein]

AFAIK the display and keyboard have a separate controller. If just the display part is stuck, the remote control via GPIB / RS232 can still work. So if remote still works, it might be only the display part.

Similar one might test, if the autoscale function still works - in the resistance mode one could measure the test current with a second DMM (e.g. with a 100 K resistor in series and without).

[bitseeker]

You might check the ribbon cable between the front panel and the main board. Disconnecting and reconnecting it may help if it has come loose or the conductors have oxidized. It's an easy thing to try, at least.

[zed65]

bitseeker, you are absolutely right! It turns out that the ribbon cable had some kind of oxidization on the pins.
Disconnect, light scrape with a knife and reconnect seems to have solved the problem (at least for now).
No more freezing:)

Thanks all!!

[bitseeker]

Glad that did the trick. They're just bare wires (well, tinned at least), so it was worth a shot. Nice meter -- I have one, too.

[lowimpedance]

Thanks for updating the fix for others future ref.  .
Next time you have it apart maybe a good idea to use some de-oxit or similar on the contacts as well.

[bitseeker]

Good idea, lowimpedance.

[Zucca]

Those are the ones I hate...  you can go down into the rabbit hole and only at the end find out it was a freacking loose contact.

Death to all bad connectors and intermittent contacts!

[zed65]

Yea, this time the rabbit hole was not so deep, I was lucky and bitseeker got me on the right track from the beginning.
I will try the de-oxit spray when I have the cover of next time.

Thanks again

[tggzzz]

Yea, this time the rabbit hole was not so deep, I was lucky and bitseeker got me on the right track from the beginning.
I will try the de-oxit spray when I have the cover of next time.

Be cautious with that. The circuits are probably very sensitive to contamination in the wrong places.

[bitseeker]

Yeah, just spray the ribbon cable ends to clean and lubricate them. It'll be enough to transfer some lubrication to the connector when you reinsert it. I'd be nervous about getting stuff on the motherboard.

[Assafl]

They are also available in pen type applicators, bottles with nail polish like brushes and wipes. All better than sprays for sensitive boards.

Or spray a cotton swab and use it to apply.

[tggzzz]

Yeah, just spray the ribbon cable ends to clean and lubricate them. It'll be enough to transfer some lubrication to the connector when you reinsert it. I'd be nervous about getting stuff on the motherboard.

Even that might be too uncontrollable. Realise you only need a very thin film over the metal parts of the connector.

If, and only if, simply moving the connector didn't dislodge oxides etc, I would try some deoxit. I'd spray a little into the aerosol's cap, and use a jeweller's screwdriver to place a tiny drop in the holes of a ribbon cable connector. That should be sufficient to coat the connector's active components.