Agilent 34401A mayhem - Page 1
Forum section: electronics / repair

author: gamerpaddy
author_rank: Regular Contributor
timestamp: October 31, 2024, 06:02:57 pm
content: So i got a 34401A for *at first glance* a fair price which turned on.later at home, i did a self test and got slapped by lots of errors. All related to "current source failed" and one AC rms full scale failed.no big deal, probably just a AD706 that had died.the "HiPot damage" writing on the top wasnt such a red flag to me as it should have.Yea.. thats probably the cause.Ian did repair such a failure in the past, no big deal it seems.i removed the ceramic hybrid and checked if its ok which it fourtainly was. all resistances matched the ones on xdev. thats 90%. good signSo i followed the path of destruction...even a trace is missing at the switcheven the red relay is welded shutoh noR104-R111C100 C101K103L101, L102, L106R118 R103K101S1all blown it seems.did they hipot test this with a lightning rod?I hope U101 isnt shot. L110 L111 look fine, seems like C101 absorbed the full blow.if its not repairable, i still got a case for my other one that seems to have visited a long distance trash bin throwing competitionand a working U102.Now, i know where to get most parts but not all.especially that red K101 relay and S1 SwitchAre there any equivalent types out there?more to come once i cleaned up this mess and got some new parts.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 31, 2024, 06:59:11 pm
content: there is a thread about this relay, but in the end it was subbed by another type, and if i recall some small pcb was madethe original relays are unobtanium unless you find some scanner cards who have them ... or something near these model ....on ebay you can still find the original front rear switch, not sure keysight still sell it, and you need to be corporate ...

author: gamerpaddy
author_rank: Regular Contributor
timestamp: October 31, 2024, 07:08:12 pm
content: apparently banging the reed relay on a table a few times got it unstuck, it now works properly again. it got low contact resistance at least.about the switch: the one on ebay wont ship to germany, but i found one on digikey that seems to fit.https://www.digikey.de/en/products/detail/c-k/F10UEE/3862504not gold plated tho.EDIT: i jumped the resistor ladder (for testing) with a 100k resistoradded a 4.7k where the 1mH coils wereput in the switch (which still works but wont latch anymore after unscheduled disassembly of the springy bit.)put in the reed relay and a cracked open omron to bend the contacts in place that had welded together.Self test pass...but no measurements at allits getting somewhere.

author: IanJ
author_rank: Unknown
timestamp: October 31, 2024, 11:37:54 pm
content: The gerbers for the pcb I designed to fix the burnt out section are on my website.Under videos go to the 34401A video page in question.Ian

author: gamerpaddy
author_rank: Regular Contributor
timestamp: November 13, 2024, 03:34:44 pm
content: Parts have arrived!luckily no ic's were harmed in this accidentits working againthanks ian, before i saw your answer i allready drew a pcb and had ordered it.i replaced both omron relays, then i just fixed the back/front switch in place as i will never use the back and it cant be sold in this condition anyways.coils, caps, resistors. and a few traces.Its measuring 0.3ohms on a short and about 500µV out at 3V compared to my other one.. neither was calibrated since 1995.edit:Zero offset cal with a very suboptimal "short" did the trickvoltage is now bang on with the other meter. resistance aswell.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 13, 2024, 05:18:15 pm
content: kudos