hp 34401A - Page 1
Forum section: electronics / repair

author: DrDiode
author_rank: Newbie
timestamp: May 26, 2017, 06:13:19 pm
content: I have an HP 34401A and it shows every decimal point on, so I don't know what the reading is I.E. a 500-ohm resistor reads 0.5.0.0.0.8.6 KO.H.Mwas hoping someone has seen this before and could give me a clue as to what to look forplease help,thanks,

author: Samogon
author_rank: Frequent Contributor
timestamp: May 26, 2017, 09:39:00 pm
content: Are they visible if you open menu?

author: james_s
author_rank: Super Contributor
timestamp: May 26, 2017, 09:54:33 pm
content: My first guess would be a shorted driver, assuming it's a multiplexed display a single shorted transistor could cause that symptom.

author: radioFlash
author_rank: Regular Contributor
timestamp: May 27, 2017, 02:10:17 am
content: Attached is the schematic from the 34401A datasheet. U603 is a SN75518FN VFD controller, the datasheet is attached. Perhaps that chip is damaged?

author: Macbeth
author_rank: Super Contributor
timestamp: May 27, 2017, 02:15:52 am
content: From lots of utterly fecked 34401A's I've seen, this display thing with all the dots appears to be a common problem. Which is perhaps a good sign that it can be fixed?

author: lowimpedance
author_rank: Super Contributor
timestamp: May 27, 2017, 01:29:25 pm
content: Quote from: Macbeth on May 27, 2017, 02:15:52 amYou have seen lots of utterly 'non operational' 34401a's ?. There are quite a few of these at work but non have gone into the 'fecked' category yet. Just curious how many you have seen.ps sorry I have nothing to add as help to the OP

author: Macbeth
author_rank: Super Contributor
timestamp: May 27, 2017, 02:17:00 pm
content: Quote from: lowimpedance on May 27, 2017, 01:29:25 pmYeah, sorry. I'm talking in particular about a pile of industrial waste sent around the world to end up as landfill in the Philippines, scavenged by desperately poor children, then finding their way to a scrap equipment dealer to be put on ebay at ludicrous prices to travel around the world again as parts units / fixer uppers. There was a thread a while ago on it and I believe TiN sourced his original rusty old 3458A from that same dealer....Found the thread.Unfortunately no pictures of the utterly fecked meters remain, but forum member free_electron posted this which may be of use to DrDiode.Quote from: free_electron

author: DrDiode
author_rank: Newbie
timestamp: May 27, 2017, 09:30:53 pm
content: yes but not all show up , the word "calibrate" comes up as "CA.LIB.RA.TE" the word "message" come up "M.ES.S.A.G.E"

author: DrDiode
author_rank: Newbie
timestamp: May 27, 2017, 09:32:09 pm
content: Thanks, I'll check it out

author: usagi
author_rank: Frequent Contributor
timestamp: June 01, 2017, 12:12:02 am
content: here is your answer.https://www.eevblog.com/forum/buysellwanted/ebay-many-faulty-hpagilent-34401a-multimers/msg811170/#msg811170

author: hendorog
author_rank: Super Contributor
timestamp: June 01, 2017, 10:27:50 am
content: Quote from: Macbeth on May 27, 2017, 02:17:00 pmFrom that pile of waste I got a 34401A for $70, and later on, an 8753C for $175 - excluding shipping which was a bitch.The 34401A has a missing fuse holder and a dim display but good otherwise. The 8753 repair has its own thread.You could say I'm dumpster diving on a laptopEdit: forgot to say that the 8753 has a Philips label on it - google says there were two Philips plants in the Philippines. NXP's website now shows only one plant there, so maybe that is where some/all of this stuff came from...Edit2: Also in the past some get a bit excited when the rear bezel is missing, and assume that means it was disassembled at some point for a dodgy repair.I suspect that is simply done to make them easier to fit into a rack or into a tight fitting panel in a manufacturing plant, because the rear bezel has a lip on it.

author: Samogon
author_rank: Frequent Contributor
timestamp: June 01, 2017, 07:39:23 pm
content: Setting aside snobbism, this pile of waste has its own food chain. And they perofrm still very good.