Agilent 34401A Startup

[Arngill]

Hi we have several 34401A's which were working fine prior to being put into (climate controlled) storage for 18 months or so. On retrieving the units and testing them, it was found that a number of them failed to power up correctly. They all follow the same sequence which is:

Power button is pressed, display comes on for about one second, display goes off, unit emits one beep of about a seconds duration, display then stays off and there is no response to any buttons apart from the "shift" key, which lights the "shift" legend on the display. It is not possible to run the self test or do anything with the unit. When it is powered off, the display flicks on for a second or so and goes off. We have about 8 of these instruments of various ages, all doing the same. I can find no service note or any reference to this behaviour anywhere within Keysight's web pages, although there are some references on the web. One person alleges this was fixed on his unit by wholesale re-soldering around the ground-referenced components in the rear of the unit, but I don't believe we have multiple HP/ Agilent units with dry joints. I have the service guide with Schematics and so far have verified that both the Floating and Ground Referenced power supplies and both the clocks are OK. The opto-couplers linking the Earthy and Floating CPU's appear to be OK. I am mystified that we have multiple units of different ages all doing the same thing. There are no Keysight Service Notes mentioning anything like this problem. 

Can anyone suggest a cause or remedy?

Thanks..

[xrunner]

Very odd. Check this thread and see if it helps -

https://www.eevblog.com/forum/testgear/hpagilent-34401a-dmm-startup-problem/

[grbk]

Can you communicate with the meters over GPIB? Try seeing if they respond to *IDN.

If you get a *IDN response, you could also see if there are any error codes, and maybe try a *RST and/or *CLS to reset them and clear the status registers.

[Zucca]

prior to being put into (climate controlled) storage for 18 months or so

More info here: was transportation smooth? were they well packaged? climate controlled means temperature and humidity constant (just to rule out the bad storage root cause)?

Did you try to move and reset the display cable to the main board?

Yes try the GPIB trick.

[Arngill]

Hi Thanks for the replies, yes, I have read the post from someone who had a similar issue. To me, it seems as if virtually any problem in either floating or grounded controllers circuitry has the potential to cause this symptom. To clarify, the storage environment these units were kept in, was temperature and humidity controlled. A couple of the units doing this are still "new" (that is to say, unused) and still in the original packaging in which they were shipped from Agilent. What I cannot understand is, if we have such a high percentage of these instruments doing this, why was it not a widespread problem with lots of people complaining about it?
I will certainly try the HPIB suggestion, so I need to get hold of an Agilent 82357A or similar.

[iMo]

Look at the resonator close to the earthy 8051. It looks many units had the 12MHz resonator replaced at the factory (manually replaced/resoldered)..

[Arngill]

Hi, Thanks for the reply. I have scoped it and get the same amplitude of 12MHz as on a working unit, but I will resolder just to sure.
Cheers

[iMo]

And the frequency should be 12MHz.. Have you checked it out?

[Arngill]

12.05MHz according to my 2465B scope. I reckon that should be close enough, ite reads about the same for the floating CPU clock. I posted this question on the Keysight Community forum as well but no answers at all from them, which is a bit of a disappointment . I just hope the HPIB can reveal something when I get the kit to try it, but I am not feeling optimistic at the moment.

[Ordinaryman1971]

So, you have few of those units... some of them are working fine I've read....
Not sure if you want to go this road but I would remove display from one of the working units and use it with one that doesn't wont to work. This way you would be able to determine if your display unit is failing or your board is causing this trouble.
Then... start troubleshooting.
For now you just have no communication between the board and the display caused.. by you don't know which one. Eliminate one of the possibilities.... well, that's what I would do.