No.104 - 3rd HP 34401A 6.5 digit Multimeter Repair
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- เผยแพร่เมื่อ 8 ส.ค. 2024
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This is the 3rd 34401A I have attempted repair on, this one reports an error 621 on TEST so lets see if it can be fixed.
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Nice fix Ian. I'm sure the videos don't always reflect the time and effort you put in to these repairs.
That was one crispy critter Tant. Nice job Ian.
Nice fix !...cheers.
Oh, wow, a cool and interesting repair video... we're supposed to be what... surprised by this? Oh, how SHOCKING, this has NEVER happened before... Ha ha ha... Seriously, thanks for making these, Ian, I really appreciate it.
I have one of these meters, had to fix a problem with the AC power switch... Nice to see you working on the guts of her... I guess I should be looking at to get the service manual...this meter has a nice bit of history; it has asset number 0001 on it, from the main R&D site of a mobile device company in Finland...so, maybe one of the first instruments purchased for the engineering team!
Still using one almost every day in our testlab.
Feedbackloop has a channel where he fixes a display that had some bad tantalums and bad inductors on the the display board. The display was brought back to a nice brightness. I believe it was video #20. Thanks for all the great videos.
By increasing the voltage on them they can be rejuvenated (filament contamination) by burning off carbon deposits. I have a couple of old 34401A displays so I guess I should give it a go. Can be hit or miss.
@@IanScottJohnston I don't believe he changed the voltages, if I remember there was an ceramic capacitor between a couple of tantalums that was shorted. And I believe one of the inductors was either open or shorted, 47uH I believe.
@@DavidSmith-zx7wz that was the repair, but there's also a rejuvenation process that Ian is describing where you overheat the elements to burn off any coatings. There's also another process that uses inductive heating of the getter patch to rejuvenate that too. These are all the same approaches used to rejuvenate CRT monitors if you're looking for more information
@@bansci Thanks for that info!
Very nice work! Keep up Ian!
Well done Ian 😃
As a starting out person, I keep looking for these, and I can never find one that's affordable... Well there was one, but it had fire damage. lol
Contact me via my website......I'll try and do you a good deal.
Excellent job Ian =D
Thank you for the video!
That was a nice and easy repair, I wish they were all like that lol!
Noooooo!.......the harder, bigger, more complex, more technical the absolute better IMHO! Then again the easier fixes are more profitable to sell on.
@@IanScottJohnston hard repairs are nice from time to time, I certainly don’t want to be doing hard repairs all the time.
First time I have seen diagram analysis where all involved components had no connections drawn :-D
Yeah, you kinda get used to HP/Agilent schematics in that regard!
Nice repair. I also got one of these old ones, from about 1993, or so, it's my go-to-guy, still fine. Maybe I also should check the capacitors some time.
Jolly good fix, for a windy Scotland🙂
Aye, it wisnae half blawin' the other nicht.
@@IanScottJohnston It's a braw bricht moonlicht nicht
@@fredflintstone1 nearly!........It's a braw bricht moonlicht nicht the nicht = it's a lovely, bright moonlit night tonight
@@IanScottJohnston but is it? 🙂
@@fredflintstone1 Squeak!!!!!!!!!!!!!!!!!!!
e621 😧
i hope one day to afford a 2nd 34401a, so that i may check it against my existing one and only beloved. which is my daily workhorse for pretty much everything.
the thing with my unit is its vfd is like this one, currently good but with the unobtainium driver ic. so the day will likely come to replace with the oled project. at which point i will need to cross check that the oled display mod. to be certain that it is not going to throw off the metter of affect the accuracy or whatever. i hope it doesn't but nobody seems to know yet (at least not for certain, we suspect it should be ok)
Thanks for sharing, I really enjoy the videos. One of my 34401A had a bad unobtanium relay. The best replacement is only good for 200V instead of 1000V. Not a big deal for my use case. These are great DMMs. Since the tantalums in these devices tend to fail at some point, would you consider replacing all tantalums or wait until they fail?
Tants are usually reliable compared to electrolytic caps, however the failure mode of tants is too much ripple can cause them to short out.
In the case of the 34401A I just repaired it’s a 20v tant on a 15v rail and these days that’s regarded as not quite enough headroom.
@@IanScottJohnston exactly. Manufacturers like AVX recommend to calculate the derating based on the expected level of ripple current - sometimes 50% derating isn‘t even enough. But due to the small derating I suspect that the likelihood of one of the tantalum’s shorting out is high, regardless of the state of the electrolytics…
@@IanScottJohnston That's not too bad 75% of rating.
We used to have a rule that we could not exceed 80% of any components rating. But as nearly all components were Mil-spec ones the caps were expected to last 25 years of service. Shelf life was not as good unless you could power them up every 5 years or so, must have been to force those little election buggers back into their place.
1.2345 Volts...reminds me that I must change the combination on my luggage.
Dang!.....thats where I remember that number from!....🙂
As a wise man once said, "It's always the capacitor."
Auch, hot air on precision instruments :( . You can see poor film capacitor bubbling and melting next to tant.... Tantalum caps easily removed with soldering iron without stressing everything off.
All blacked FR4 need to be removed too, not left there to cause huge leakage.
Fair point.
@@pa1wbu tantalum caps of that type have flexible leaf terminals. So one can heat up one side, lift it like 10-15 degrees up off the board pad. Then go from other side and remove cap. No need two iron yoga exercises :)