Got myself an Agilent 34401A, with a label "not working" on it - Page 1
Forum section: electronics / testgear

author: MrSadman
author_rank: Contributor
timestamp: October 01, 2013, 07:56:50 am
content: Well I got an Agilent 34401A fo free. Condition:So, I am going to see, if I can figure out what's wrong with it and maybe even fix it.I haven't really had the time to start any serious debugging yet, but maybe someone here has more experience with fixing DMM-s then me.The problem description sofar:"The multimeter doesn't measure voltages under 10V and also might have problems with measuring resistance, current measuring works fine" - I have not had the chance to verify any of this yet.Self test returns errors:612 - Ohms 500 nA source failed. This test configures to the 10 V dc rangewith the internal 10 M 100:1 divider U102A connected across the input.The 500 nA ohms current source is connected to produce a nominal 5 Vsignal. A 20 ms ADC measurement is performed and the result ischecked against a limit of 5 V ± 1 V.613 - Ohms 5 uA source failed. This test configures to the 10 V dc rangewith the internal 10 M 100:1 divider U102A connected across the input.The 5 ?A ohms current source is connected. The compliance limit of thecurrent source is measured. A 20 ms ADC measurement is performedand the result is checked against a limit of 7.5 V ± 3 V.I think my first move is to go over the troubleshooting hints in the service manual and see if that brings anything up.Feel free to give me any hints or ideas

author: nctnico
author_rank: Super Contributor
timestamp: October 01, 2013, 01:57:36 pm
content: Feed the model number and error codes to Google and see what comes up. Chances are its a common problem.

author: free_electron
author_rank: Super Contributor
timestamp: October 01, 2013, 03:00:35 pm
content: There is two possibilities for this problem.Offt he top off my head, i don't have the schematic handy-the precision hybrid is damaged. That is not repairable. The hybrid costs 400$...- the pathway around the hybrid is damaged. There are some external components.I will look it up in a moment. I've seen those problems before.

author: echen1024
author_rank: Super Contributor
timestamp: October 01, 2013, 04:58:32 pm
content: Where did you get this meter?

author: MrSadman
author_rank: Contributor
timestamp: October 01, 2013, 06:36:01 pm
content: Quote from: nctnico on October 01, 2013, 01:57:36 pmI have spent some time trying to Google this issue, but so far I haven't found anything regarding these error codes. Although I have to say, my Googling skills have been quite poor these past two weeks. Took me about 30 minutes to find someone selling stackable banana-banana patch cables.Quote from: free_electron on October 01, 2013, 03:00:35 pmAny input is a lot of help, thank you. At the moment it seems though, that I wont have a chance to take a look inside the device till the weekendQuote from: echen1024 on October 01, 2013, 04:58:32 pmI got the meter from my workplace. It has probably about 7-8 years of working hours on it.

author: MrSadman
author_rank: Contributor
timestamp: October 05, 2013, 07:55:28 am
content: Having a first look inside todayIn the mean time, here's a gut shot.

author: free_electron
author_rank: Super Contributor
timestamp: October 05, 2013, 09:14:17 am
content: The hybris is the big grey ceramic chip with the white sticker on it.Check the 9 megaohm path first. I've seen those open...The schematic tells you where it is

author: MrSadman
author_rank: Contributor
timestamp: October 05, 2013, 10:44:09 am
content: Think you might be right. While there are no shorts or open contacts a lot of the resistances are more then 10% off and some are over 100% off, some are smaller and some are larger. The resistances that are way off are from the DC Amp and Ohms schematic so the self test errors seem to be linked.