HP/Agilent 34401A - Error 745 - Page 1
Forum section: electronics / repair

author: ltktomas
author_rank: Contributor
timestamp: August 21, 2016, 07:06:38 pm
content: Hia few days ago, when I was using one of my 34401A, it started to show error 745 since powering up.User Guide says that this error means:Cal checksum failed, FRES corrections.Interesting is If I let the instrument warm up, after about 5 minutes when I shut it down and then I switch it back on, the error disappears. But if I cool down the EEPROM chip (U505) on PCB, this error comes back. So I took soldering pen (maybe cold joints), but no changes.So do you think the EEPROM is faulty or (and I hope for this) it starts to "forget" ?Last calibration was performed in Dec 1999 and I think that this cool down/warm up thing only changes Vgs of a transistor inside the EEPROM that carries the CAL informations (so sometimes the information is 1 and sometimes is 0), so it could be repaired only by rewriting -> performing new calibration. What do you think ?

author: plesa
author_rank: Frequent Contributor
timestamp: August 21, 2016, 07:32:38 pm
content: Try to recalibrate and if it does not help order U505 from Keysight (U505 Keysight order code: 1818-5236 Description:IC 4K EEPROM 500-ns ).

author: voltsandjolts
author_rank: Unknown
timestamp: August 21, 2016, 07:49:38 pm
content: Discussed here:https://www.eevblog.com/forum/repair/agilent-34401a-selftest-ok-but-20-errors-(cal-checksum-failed)/

author: Jwalling
author_rank: Unknown
timestamp: August 21, 2016, 07:50:02 pm
content: There's a document on Keysight that deals with this but I can't find it at the moment.This may help:http://www.azrefs.org/subject-a-guideline-to-fix-the-740-series-self-test-errors-for.html

author: ltktomas
author_rank: Contributor
timestamp: August 21, 2016, 09:03:18 pm
content: Quote from: voltsandjolts on August 21, 2016, 07:49:38 pmYes, I've already read this discussion. But the difference is that main says only Error 745 and only when it is not warmed up.I'll see what's going to happen after the calibration procedure. I just hope that the EEPROM chip started to forget after 17 years

author: plesa
author_rank: Frequent Contributor
timestamp: August 22, 2016, 06:13:18 pm
content: Before calibration, just try to un-secure calibration and secure it again.By change of the EEPROM you will also upgrade the firmware if your unit is old.There are some communication and other improvement.

author: chihaxinh
author_rank: Regular Contributor
timestamp: August 24, 2016, 01:33:06 am
content: Hi PlesaHow to upgrade firmware agilent 34401a ?

author: plesa
author_rank: Frequent Contributor
timestamp: August 26, 2016, 11:26:36 am
content: Few 34401A has a socket for U502, so you needs only programmer and extractor. Majority of units requires to desolder U502.Chip U502 aka 34401-88806 Prog EPROM is M27C2001-12C1E IC 2M-BIT OTP 120-ns CMOS.But the parts is no longer available, so I'm still looking for unit with more recent version.Version 10 can be found on TiN websitehttps://xdevs.com/fix/hp34401a/From 34401A manual:"first number is the firmware revision number for the measurement processor the second is for the input/output processor and the third is for the front-panel processor"

author: xs.over
author_rank: Newbie
timestamp: June 20, 2024, 06:38:52 pm
content: Quote from: ltktomas on August 21, 2016, 07:06:38 pmHello. Sorry to grave dig an ancient thread.Have you resolved the error 745 on your 34401a multimeter? What's the right solution - to replace EPROM U502 IC?Thanks