hp 34401A

[DrDiode]

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.M


was hoping someone has seen this before and could give me a clue as to what to look for

please help,

thanks,

[Samogon]

Are they visible if you open menu?

[james_s]

My first guess would be a shorted driver, assuming it's a multiplexed display a single shorted transistor could cause that symptom.

[radioFlash]

Attached is the schematic from the 34401A datasheet. U603 is a SN75518FN VFD controller, the datasheet is attached. Perhaps that chip is damaged?

[Macbeth]

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?

[lowimpedance]

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?

You 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 

[Macbeth]

You 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 

Yeah, 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.

those dots are caused by leaky VFD drivers. they are TI parts. obsolete and replaced by pericom . i have posted the xref before on the forum.

these are 32 bit high voltage shift registers in plcc44 package. replace em and the problem is solved.

[DrDiode]

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"

[DrDiode]

Thanks, I'll check it out

[usagi]

here is your answer.

https://www.eevblog.com/forum/buysellwanted/ebay-many-faulty-hpagilent-34401a-multimers/msg811170/#msg811170

[hendorog]

You 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 

Yeah, 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.

those dots are caused by leaky VFD drivers. they are TI parts. obsolete and replaced by pericom . i have posted the xref before on the forum.

these are 32 bit high voltage shift registers in plcc44 package. replace em and the problem is solved.

From 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 laptop

Edit: 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.

[Samogon]

Setting aside snobbism, this pile of waste has its own food chain. And they perofrm still very good.