Magic smoke blows up! 34401A

[bdunham7]

The spring is on both sides of the board?

What you have circles are the burnt ashes of the board where it was arcing and flaming.  There's no wire there that I can see.

[Wolfgang]

The only fitting comment for this one is Monty Pythons dead parrot sketch. 

[dimmog]

I wonder if someone seriously exceeded the common mode voltage limit with a high energy source.

That's probably the best guess so far.  Perhaps trying to measure the current of a high-voltage source like a MOT or worse?  I'd like to see the case and covers around that area.

In that case, transformer might have arced over inside and inguard logic might be toasted too, first thing I would test is supply inguard with 5V logic voltage and see, if it's shorted. If so, that thing is a paper weight and only useful as a source for case parts, which actually still look quite good 

Main fuse was blown but transformer is good, display board works. Hole in U101 is a little worrying 🙂 but meter surprisingly starts up.

[kcbrown]

Main fuse was blown but transformer is good, display board works. Hole in U101 is a little worrying 🙂 but meter surprisingly starts up.

 

[bdunham7]

Main fuse was blown but transformer is good, display board works. Hole in U101 is a little worrying 🙂 but meter surprisingly starts up.

Put it back on eBay, as-is.   "Powers up but no further testing done"

[dimmog]

Looks like the MOVs and GDTs are all there.  The trace may have saved it from further damage.  Maybe the current owner will clean it up and post a few pictures.

Yep, all 3 MOVs and 2 arrestors are intact. Spark gaps are fine and look undamaged. Front/rear switch was in rear position and stuck in it completely.

[Cerebus]

Main fuse was blown but transformer is good,

Might be worth a check that the isolation between the various transformer windings has held up. The transformer might work for some value of "work" but might have developed enough leakage that it'd completely bugger things in a measurement taking situation.

[dimmog]

Main fuse was blown but transformer is good,

Might be worth a check that the isolation between the various transformer windings has held up. The transformer might work for some value of "work" but might have developed enough leakage that it'd completely bugger things in a measurement taking situation.

That's a good point.

[joeqsmith]

They were not trying to measure current with it and had some foil in there?   

[tooki]

OK, you win, that is the ugliest 34401A I've seen to date(and I bought one that had a hole drilled all the way through case and board).

I've been trying to figure out what demented company it is that drills their TE before selling it to the surplus dealers.  Any idea?  And b/t/w, I know first okay, second hand that whoever they are, their selling agent does not disclose that the items have been drilled.

They don’t sell them to surplus dealers, they dispose of them as scrap. (In fact, they may have spent money to dispose of it.) The destruction is due to accounting: once amortized (= zero residual value on paper) they have to prove they disposed of it. If they were to sell it, then it’d mean it still “has value” and thus cause accounting headaches. I’m not an accountant so I don’t know the whole details, I just know that making mistakes can cause problems with the tax man, so companies often take the easiest “safe” way out, which is to ensure the discarded equipment is not reusable.

Is it morally repugnant? IMHO absolutely. Is it wasteful? Grotesquely. Could they avoid it? Yup, absolutely. But it’d take effort that bean counters don’t like to exert.

So how does equipment like that end up on eBay? Easy: someone grabbed it out of the dumpster or nicked it from a recycler. It wasn’t intended to be resold, indeed, having been deliberately ruined to prevent resale.

[mawyatt]

About 30 years ago IBM closed a development team down and had a truck arrive that crushed all the new lab equipment. Over $10M of new Tek, HP and R&S equipment was crushed into a junk pile. I had asked why couldn't they have donated it to some university, the answer I got was "accounting", whatever that meant I still don't know

Best,

[Per Hansson]

I would like to hear the story behind it.

Me too!
dimmog, please send the pics to the eBay seller and ask if they can divulge what happened to it, I'm dying to know 

[Paceguy]

Looks far gone, but I would suggest that you keep it as a parts unit. The display and some other parts that could be used in the future repairs.

[Swainster]

Occasional lurker here. Your post convinced me to sign up 

By coincidence, last week I bought a couple of "parts only" non working agilent marked 34401a multimeters. I was pretty unhappy when I found that the newer one (latest main PCBA version, i.e. newer than the one listed in the keysight manual) had the front terminal 'common' trace blown off the PCB all the way back to the front/rear selector switch, and the floating ground vapourised where it passes under U102. Incidentally, the voltage reference had gone missing so I assume a previous owner had already salvaged it  . Your meter makes mine look pristine 

In slight compensation, the other non-working meter just decided to start working after I started poking around inside it, before I had actually repaired anything.

For a challenge, I have decided to repair the zapped multimeter, and initial investigation shows that the -18V rail regulator has died (possibly related to the burnt traces?), and let -36V unfiltered through the system. This has probably not done any of the floating analog circuitry any favours, and has definitely toasted the display silicon, though the still VFD looks ok. Swapping the display over from the working meter shows that the floating logic is still working, which gives me some hope. Early stages yet, but the current jobs are to replace the LM337 negative rail regulator and an AD711 which seems to be stopping the ADC from working. Fingers crossed that will clear the 604 error and allow me to move on to the next fault. At some point I will need to pick up a replacement display board.

[TheSteve]

Occasional lurker here. Your post convinced me to sign up 

By coincidence, last week I bought a couple of "parts only" non working agilent marked 34401a multimeters. I was pretty unhappy when I found that the newer one (latest main PCBA version, i.e. newer than the one listed in the keysight manual) had the front terminal 'common' trace blown off the PCB all the way back to the front/rear selector switch, and the floating ground vapourised where it passes under U102. Incidentally, the voltage reference had gone missing so I assume a previous owner had already salvaged it  . Your meter makes mine look pristine 

In slight compensation, the other non-working meter just decided to start working after I started poking around inside it, before I had actually repaired anything.

For a challenge, I have decided to repair the zapped multimeter, and initial investigation shows that the -18V rail regulator has died (possibly related to the burnt traces?), and let -36V unfiltered through the system. This has probably not done any of the floating analog circuitry any favours, and has definitely toasted the display silicon, though the still VFD looks ok. Swapping the display over from the working meter shows that the floating logic is still working, which gives me some hope. Early stages yet, but the current jobs are to replace the LM337 negative rail regulator and an AD711 which seems to be stopping the ADC from working. Fingers crossed that will clear the 604 error and allow me to move on to the next fault. At some point I will need to pick up a replacement display board.

Welcome to the forum! Feel free to start a thread in the repair section to document your 34401A repair, I'm sure we'd all like to see your progress.

[Swainster]

Thanks! Was just thinking the same thing. A few parts should arrive on Friday so I'll try to post something over the weekend.

[tooki]

About 30 years ago IBM closed a development team down and had a truck arrive that crushed all the new lab equipment. Over $10M of new Tek, HP and R&S equipment was crushed into a junk pile. I had asked why couldn't they have donated it to some university, the answer I got was "accounting", whatever that meant I still don't know

Best,

It means “we wanted to write it off as a loss on our taxes”. 😭

[bc888]

Wow wow wow.

Seller has a 99.5 rating. $150 seems like a solid price. "Condition:For parts or not working  “unit looks very good”. The pictures make it look great.