Magic smoke blows up! 34401A - Page 1
Forum section: electronics / testgear

author: dimmog
author_rank: Regular Contributor
timestamp: October 03, 2021, 06:23:55 pm
content: Latest ebay find. Magic smoke blows up here!Poor HP/Agilent 34401A

author: TheSteve
author_rank: Unknown
timestamp: October 03, 2021, 06:27:27 pm
content: 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).

author: Gyro
author_rank: Super Contributor
timestamp: October 03, 2021, 06:28:56 pm
content: Wow. Did somebody try to measure lightning?At least the MOVs and Spark gap look intact!

author: Specmaster
author_rank: Super Contributor
timestamp: October 03, 2021, 06:34:04 pm
content: Quote from: dimmog on October 03, 2021, 06:23:55 pmWow, thats fit for the bin, did you buy it and it blew up or what?

author: strawberry
author_rank: Super Contributor
timestamp: October 03, 2021, 06:38:59 pm
content: Challenge acceptedI think, front end should be still alive

author: thinkfat
author_rank: Unknown
timestamp: October 03, 2021, 06:39:04 pm
content: That's just too far gone.

author: dimmog
author_rank: Regular Contributor
timestamp: October 03, 2021, 06:52:06 pm
content: Quote from: Specmaster on October 03, 2021, 06:34:04 pmI bought it on ebayhttps://www.ebay.com/itm/255153918046A little worried about the pungent smell of burning right out of the shipping box.

author: xrunner
author_rank: Super Contributor
timestamp: October 03, 2021, 07:06:17 pm
content: Quote from: dimmog on October 03, 2021, 06:52:06 pmI think your deal stinks.

author: Cerebus
author_rank: Super Contributor
timestamp: October 03, 2021, 07:15:27 pm
content: Wow, you've got to try quite hard to do that much damage to a 34401A.

author: Cerebus
author_rank: Super Contributor
timestamp: October 03, 2021, 07:23:08 pm
content: Quote from: Gyro on October 03, 2021, 06:28:56 pmTwoof the MOVs look intact. There should be athirdMOV to the side of the front terminals. I don't think it's there any more!

author: Gyro
author_rank: Super Contributor
timestamp: October 03, 2021, 07:29:53 pm
content: Looking at the first (wider scale) photo in the OP, the third one may actually still be there too.I wonder if someone seriously exceeded the common mode voltage limit with a high energy source.

author: floobydust
author_rank: Super Contributor
timestamp: October 03, 2021, 07:35:53 pm
content: It carbon tracked and arced to the Front Panel board, all is toast. Exploded PLCC, kapton tape on the electrolytic tops?Only seen this much carnage with a MOT and someone extra stupid to let it arc for a very long time.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 03, 2021, 07:51:53 pm
content: Good grief... whomever did that should be made to lick the pcb clean.Whilst it's true anything can be repaired, the time and cost to fix that would be completely impractical. Hopefully there are enough surviving parts to recoup some of your costs!I wonder if we should add a new award to the TEA thread, "The McCoy Award", or the "Dead Parrot Award" both spring to mind.

author: bdunham7
author_rank: Super Contributor
timestamp: October 03, 2021, 07:58:10 pm
content: Quote from: TheSteve on October 03, 2021, 06:27:27 pmI'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 knowfirstokay, second hand that whoever they are, their selling agent does not disclose that the items have been drilled.

author: TheSteve
author_rank: Unknown
timestamp: October 03, 2021, 08:00:37 pm
content: Quote from: floobydust on October 03, 2021, 07:35:53 pmKapton tape on top of the electrolytic caps is factory."What do we have on the spacecraft that's good?" seems appropriate here.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 03, 2021, 08:02:24 pm
content: Quote from: bdunham7 on October 03, 2021, 07:58:10 pmDemilitarisation?Surely not disclosing this sort of thing will result in a marked lack of repeat customers?

author: TheSteve
author_rank: Unknown
timestamp: October 03, 2021, 08:03:32 pm
content: Quote from: bdunham7 on October 03, 2021, 07:58:10 pmWell in my case it was advertised that a hole had been drilled through the entire thing, and it was pretty obvious looking at the case. That is what made me want it(yeah, I'm broken). Someday I'll post the repair of my Datron 4920M that had been decommissioned by hammer.34401A repair:https://www.eevblog.com/forum/repair/34401a-repair-(had-a-hole-drilled-through-it)/I have some parts 34401A PCB's, wonder if a working unit could be made.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 03, 2021, 08:18:11 pm
content: Quote from: bdunham7 on October 03, 2021, 07:58:10 pmThe only place that I've ever seen that done was on De-Militarized equipment.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 03, 2021, 09:42:51 pm
content: I would like to hear the story behind it.

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 03, 2021, 09:49:35 pm
content: Quote from: joeqsmith on October 03, 2021, 09:42:51 pmI’ll second that. If the person was still upright when it was over, I’ll bet they needed a clean pair of tighty whities.A Jerry Lee Lewis song lyric comes to mind: “Goodness gracious, great balls of fire”That had to be several kilovolts to create that area of flash-over, unless the board was contaminated. Even so, it would take some mighty high voltage to do that and more than a few watts required to vaporize that missing MOV. Scary stuff.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 03, 2021, 10:17:45 pm
content: 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.

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 03, 2021, 11:02:32 pm
content: Ah, you’re correct. I thought RV101 was missing but it turns out it is a black device, not the blue, somewhat hidden in the shadows. It does appear that R104 and 105 in the input chain are vaporized, I mistook that area for RV101.

author: bdunham7
author_rank: Super Contributor
timestamp: October 03, 2021, 11:12:37 pm
content: Quote from: Gyro on October 03, 2021, 07:29:53 pmThat'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.

author: MadTux
author_rank: Frequent Contributor
timestamp: October 03, 2021, 11:21:35 pm
content: Quote from: bdunham7 on October 03, 2021, 11:12:37 pmIn 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

author: Cerebus
author_rank: Super Contributor
timestamp: October 04, 2021, 12:07:13 am
content: Quote from: Johnny10 on October 03, 2021, 11:18:26 pmNot wires, you're seeing the spring on the switch which just happens to coincide with the edges of the area of PCB that's bubbled up.

author: bdunham7
author_rank: Super Contributor
timestamp: October 04, 2021, 12:14:18 am
content: Quote from: Johnny10 on October 04, 2021, 12:10:58 amWhat 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.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2021, 12:16:43 am
content: The only fitting comment for this one is Monty Pythons dead parrot sketch.

author: dimmog
author_rank: Regular Contributor
timestamp: October 04, 2021, 12:47:15 am
content: Quote from: MadTux on October 03, 2021, 11:21:35 pmMain fuse was blown but transformer is good, display board works. Hole in U101 is a little worrying 🙂 but meter surprisingly starts up.

author: kcbrown
author_rank: Frequent Contributor
timestamp: October 04, 2021, 12:57:59 am
content: Quote from: dimmog on October 04, 2021, 12:47:15 am

author: bdunham7
author_rank: Super Contributor
timestamp: October 04, 2021, 01:02:23 am
content: Quote from: dimmog on October 04, 2021, 12:47:15 amPut it back on eBay, as-is. "Powers up but no further testing done"

author: dimmog
author_rank: Regular Contributor
timestamp: October 04, 2021, 01:02:49 am
content: Quote from: joeqsmith on October 03, 2021, 10:17:45 pmYep, 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.

author: Cerebus
author_rank: Super Contributor
timestamp: October 04, 2021, 01:05:09 am
content: Quote from: dimmog on October 04, 2021, 12:47:15 amMight 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.

author: dimmog
author_rank: Regular Contributor
timestamp: October 04, 2021, 01:13:58 am
content: Quote from: Cerebus on October 04, 2021, 01:05:09 amThat's a good point.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 04, 2021, 01:30:23 am
content: They were not trying to measure current with it and had some foil in there?

author: tooki
author_rank: Super Contributor
timestamp: October 04, 2021, 05:10:28 pm
content: Quote from: bdunham7 on October 03, 2021, 07:58:10 pmThey don’t sell them to surplus dealers, they dispose of them as scrap. (In fact, they may havespentmoney 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 topreventresale.

author: mawyatt
author_rank: Super Contributor
timestamp: October 04, 2021, 05:26:40 pm
content: 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 knowBest,

author: Per Hansson
author_rank: Unknown
timestamp: October 04, 2021, 05:36:09 pm
content: Quote from: joeqsmith on October 03, 2021, 09:42:51 pmMe 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

author: Paceguy
author_rank: Regular Contributor
timestamp: October 04, 2021, 06:12:50 pm
content: 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.

author: Swainster
author_rank: Frequent Contributor
timestamp: October 05, 2021, 06:25:29 am
content: Occasional lurker here. Your post convinced me to sign upBy 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 pristineIn 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.

author: TheSteve
author_rank: Unknown
timestamp: October 05, 2021, 02:45:36 pm
content: Quote from: Swainster on October 05, 2021, 06:25:29 amWelcome 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.

author: Swainster
author_rank: Frequent Contributor
timestamp: October 05, 2021, 03:12:36 pm
content: Thanks! Was just thinking the same thing. A few parts should arrive on Friday so I'll try to post something over the weekend.

author: tooki
author_rank: Super Contributor
timestamp: October 05, 2021, 06:50:44 pm
content: Quote from: mawyatt on October 04, 2021, 05:26:40 pmIt means “we wanted to write it off as a loss on our taxes”. 😭

author: bc888
author_rank: Regular Contributor
timestamp: October 06, 2021, 01:00:09 am
content: 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.