Another 34401A Repair Question - Page 1
Forum section: electronics / repair

author: smgvbest
author_rank: Unknown
timestamp: October 29, 2015, 01:09:41 am
content: Hi I got a deal on eBay (of course) for an as-is 34401A.After getting down on my test bench I cleared the previous messages and ran a full self test which is passed.Ok so good. surprised but good. Next I started testing it out and on DCV the 0-10V ranges are off by as much as 700mvbut greater than 10V (up 30v far as my power supply will go) is't dead on.I'm thinking maybe a failed Cal?but could be a real problemIs it possible to calibrate only the 0-10V ranges or do you have to cal the entire unit?

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: October 29, 2015, 01:35:23 am
content: Could be a failed cal. Have you tried shorting the inputs on all DCV ranges? They should read close to zero. The calibration manual lists the specs in Chapter 4.The 10V range has the offset cal (shorted input) and gain cal (10V). There is also a -10V cal that is recommended after a/d servicing or replacement of cal ram. Perhaps the cal ram has a problem? I think there have been a few members with the bad U505.I can't tell you about doing individual ranges but you can probably find an answer in one of the several 34401A repair threads.

author: deadlylover
author_rank: Frequent Contributor
timestamp: October 29, 2015, 04:23:09 am
content: You can adjust the individual gain ranges no problem, except the zero offset adjustment, which will do it for all ranges automatically.

author: Dr. Frank
author_rank: Super Contributor
timestamp: October 29, 2015, 09:49:28 am
content: Yes, I also can confirm, that the different ranges of the 34401A can independently be calibrated, regarding gain factors.Anyhow, the -10V calibration affects linearity for all ranges.Linearity and polarity inversion should be checked before attempting to re-calibrate the instrument, especially the -10V item; afaik, this is required only after A/D replacement, and should not be done routinely.Frank

author: KSP
author_rank: Regular Contributor
timestamp: October 29, 2015, 01:20:19 pm
content: I can also confirm that you can calibrate individual ranges at full scale. As stated before, the zero cal will automatically run for all ranges. Just apply a good 10V source, set cal range to 10V and press enter. Manuals are available on the Keysight website if you need more info, but getting to the cal menu is simple enough

author: smgvbest
author_rank: Unknown
timestamp: October 29, 2015, 10:17:07 pm
content: Thank you all for the replies. I'll do the zero cal then the gain for up to 10V and see if that resolves the issue.now to go re-read the procedure on how to cal it.

author: smgvbest
author_rank: Unknown
timestamp: November 06, 2015, 02:14:47 am
content: Just wanted to give an updateI've done a zero cal and the DCV from 100mV to 10V front and rear and those ranges are now atleast as accurate as my DM3068.No cal errors and its been working well since. I was unable to do a cal on the DCI as it looked like I missed the fact there is no 3amp fuse in the rear holder. as well as no fuse cap that should be there. so will need to order from keysight.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: November 06, 2015, 02:35:51 am
content: Good to see you got it fixed.

author: siggi
author_rank: Regular Contributor
timestamp: November 06, 2015, 11:39:43 am
content: Quote from: smgvbest on November 06, 2015, 02:14:47 amI got a replacement from Digikey, see this thread for the part numbers that fit:https://www.eevblog.com/forum/index.php?topic=49877Sent from my iPad using Tapatalk

author: smgvbest
author_rank: Unknown
timestamp: November 06, 2015, 07:06:40 pm
content: Thank youI already order from keysight, had no trouble actually it's part number 2110-0869 @ 14.79. I had a few other cosmetic things I wanted to order so worked out with keysight, free express shipping over $50 which I had.