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No.106 - 4th Agilent 34401A 6.5 digit Multimeter Repair
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- čas přidán 24. 03. 2023
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This DMM exhibits a problem on the inputs I haven't seen before on these particular meters.
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Nice repair 👍
Seen that precision resistor fail before now but never the inductors, good fix!
I do enjoy your repair videos.
Great job Ian.
It's a great feeling when you first turn on the equipment after you have carried out a repair and see that it is working correctly. It gives you a real buzz, no matter how many times you do it. As I gain more experience, I am surprised what I can now successfully tackle with a good outcome.
Thanks for sharing. 😉👍
My recent supplier of DMM's thought it odd I only wanted the faulty stuff!......but it's for the exact reasons you mention, and every day is a learning day no matter who you are. Can't beat the journey!
@@IanScottJohnston Absolutely! I have been a hobbyist for about 10 years now. I have gained confidence as time and experience passes. I now look back at some of the things that stumped me many years ago and find it hard to believe that I didn't identify the problems earlier. But hey, that is what learning and experience is all about. I now have the opportunity to share what I have leaned on my channel too. Hope you don't mind, here is the link czcams.com/users/MiracleMAX
Keep up the good work and continue sharing your repairs 😁😁
Ian, another great troubleshooting video, thanks for your efforts and products.
There's always something that can be learned from watching your video's
And that is don't give up
what a great fix. always good to see your videos 🙂
@6:15 my suggestion for that is to heat the PCB from underneath with the hot air, it works well if you are trying to avoid damaging stuff near by, unless of course there is stuff underneath that prevents it.
Or just unsolder the other components that could be damaged first.
No components underside, but that big red thing is a reed relay and it's unobtainium, manufactured specifically for HP devices......I'd be hesitant to heat the board from the underside for the worry of getting heat anywhere near it. Didn't want to desolder those relays either for the same reason.
The heat guard method works quite well, just keep the guard touching the Pcb at all times to stop airflow going underneath it, and keep it as low profile as you can so it's not in the way. I sometimes use masking tape to keep them in place. Works very well.
PS. Usually use 1mm aluminium, easily cut/bent to shape.
Love your videos...Nice work!
Very good presentation. Thank you for sharing.
Wonderful job!!!
As always, a great video. Thx Ian
Nice repair! Probably someone tried measuring mains voltage using the current range ;)
This 5Ω shunt resistor is quite critical, as it dissipates 50mW @ 100mA. Therefore it needs to be a very low T. C. type. The original thin film one in my 34401A on the other hand showed a large timely drift, especially under full load. It seemed to me, that hp could not find resistors with both stable characteristics
I fitted a 1W precision resistor compared to the 0.125W which the spec asks for. I even contemplated potting it to help furher. I could have fitted something better I am sure, but it's still tough getting parts these days!
@@IanScottJohnston Years ago, I exchanged the TF resistor by a precision wire wound from G.R. The timely drift was much better, but its ~5ppm/K lead to a big power drift and therefore non linear behavior, i.e. big deviation at 10mA vs. 100mA level. Of course, @100mA it took half a minute, or so, until the reading stabilized. If I remember correctly, that deviation was then out of spec. So I re-assembled the TF resistor again. Does not bother me any more, as I later got a 34465A, which uses more and lower valued shunt resistors.
Component Allocation meanwhile is practically over, whereas special parts might remain a permanent problem. COTO low e.m.f. / HV relays are unobtainium for years.
Super!
Nice repair, but what was the current path that took all these parts out?
What would give me some concerns is where was all that current flowing, what other parts have been over stressed. Was it just a high current fault that the fuse did not catch and all the components that passed away to the Weee bin in the sky were in that path? But the size of the inductors did not look like they were up to that many amps.
I didn't analyse too much because it could have been measuring mains AC in resistance mode, large voltage spikes i.e. many k's......who knows.
The last test on the diode showed the 2 last digits going nuts!
Why is that? Junction noise? I've never noticed it, cuz I have cheap test equipment.
Great video. Thanks 👍
I would have unsoldered the relay and that big blue capacitor first to make removing the SMD components easier. I have some boards from VCRs with lots of inductors of various values on them. I would've used some of them. What are L101 and L106 actually for anyway and why are there 3.16K resistors in parallel with them. 1mH is quite a high value for the small size of package. They must be 100s of turns of really thin wire.
Those relays are unobtanium so folks are saying on the forum so didn't want to disturb them. It looked tighter than it was to work on, not too bad.......
Great fix Ian. Did you chin the owner about the the cause of the failure?
No, they acquired it faulty.
👌but now I want to now more about that resistance box of course.
Home made:
100ohm Vishay Zseries 0.005% 0.2ppm/degC
1Kohm Vishay Zseries 0.005% 0.2ppm/degC
10Kohm Vishay Zseries 0.005% 0.2ppm/degC
100K Vishay VHP101 series 0.1% 0.0ppm/degC
Still need to characterize the values against my 3458A, but probably after I upgrade all resistors to VHP101 type.
@@IanScottJohnston Thanks for the list. Those VHP10x are Impressive components. 'Call for Quote' they say, that sounds expensive too.
They are pretty expensive.......hence I'm in no hurry!
Great video....cheers!
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@@fredflintstone1 Squeak !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Do you have an AC reference source ?
HP 3245A Universal Source
Ian, is there a source of VFDs for these? I'm looking at picking one up myself, but the quality of the VFD always makes me nervous!
I have bought about 3 via Ebay and different sellers....always works out pretty good.
@@IanScottJohnston cheers ian
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It can be tricky, I think instructions are in the service manual.