34401A

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작성자장사의신 조회 52회 작성일 2021-12-29 08:25:01 댓글 0

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Video Blog #082 - HP 34401A 6.5 digit Multimeter Repair - Part 2

In this video I continue repair of an HP 34401A 6.5 digit Multimeter. I show to replace the VFD display without damaging the PCB and offer up an explanation as to why the display board has it's own virtual ground.

Part 1 is here:-


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alpcns : Lovely meter, and great repair, as always. I loved the explanation of the (initially complicated, in my eyes) power supply to the microcontroller. Your detailed explanation of their rationale makes a lot of sense, of course, but I sure didn't think of it - which explains why I am better at blowing up stuff ;-)

Have a very Merry Christmas and a happy, healthy New Year!
GadgetUK164 - Retro Gaming Repairs & Mods : Superb job Ian =D Great to see this meter returned to tip top condition! Have a great Christmas and New Year if I don't speak to you before then =D
ptronix : Did exactly the same job on my meter Ian & the Chinese sourced vfd is still good 5 years later
AllTheGearNoIdea : I’m amazed you got a replacement VFD great repair. Merry Christmas and happy new year to you and the family. Regards Chris
SeanBZA : That VFD driver normally has a 5V supply and a -36V supply to drive the VFD, with the filament being normally 3-6VAC, supplied from either a separate power winding on the transformer, or from a small isolated inverter block on the board, both with a centre tap. The reason Agilent went for the 18V supplies was likely because they likely did not want to have another winding on the transformer, to supply a -36V rail, or have an on front panel DC-DC converter unit to provide the -36V and the filament supply. That NEC microcontroller, with different mask ROM versions has been used in a lot of equipment, as it has enough IO pins to make it useful, plus also has the VFD drive and a few integrated peripherals on it. It has been used on many pieces of consumer equipment.

The power transformer is common to many of the instruments, and they did not want to put extra windings there, that would be unused most of the time. The 18V rails are already there for the analogue stuff, so makes sense to use them to draw that extra current, and using both rails also ensures most of the current does not flow into the 0V rail, with only a tiny constant current from the driver being in the 0V rail. Level shifters for the clock and data into the display is then cheaper, and lower board space, as it is in otherwise unused volume under the display, while putting the DC-DC converter would limit the case volume behind the board, and in a 6.5 digit meter this would also need to have a really good magnetic and electrical shield (likely a fully soldered tin plated steel can) sticking right into the area above the sensitive input circuitry. Instead you just have the 2 steel shielding plates, connected via a RF ground to the chassis, to remove the display switching, and this works well.

34401A Digital Multimeter, 6.5 Digit DMM Product Demonstration

http://www.keysight.com/find/34401a The Keysight 34401A is the industries most popular 6.5 digit digital multimeter. The 34401A is a true multimeter as it offers DCV, ACV, DC and AC current, 2 and 4 wire resistance, frequency, period, diode test and much more. It is easy to use on the bench and provides 1000 rdgs/s in a system.
Leila : what is the lowest AC current it can measure
Alberto Ignacio López Sandoval Ω : The Best multimeter it's Agilent
Galo Freire : I have one

#2 Repair of Agilent 34401A Multimeter

In this episode, I repair a broken Agilent 34401A multimeter.

Previous repair of HP E3620 power supply: https://www.youtube.com/watch?v=x2hfi6Ts5Bk
Dennis Lubert : I found that for such big smd pin pitches these small tips are not only not necessary, but make working a bit more difficult by having much lower thermal mass. Having a good chisel tip you can easily solder these too (get some scrap boards and desolder and solder again and after a few you get the hang of it). I think there are some eevblog or so videos about good techniques with that tip too. Some people like Louis Rossman love other weird shapes too, but they are usually bigger and once you got used to them, they are much more versatile and quicker than changing tips all the time. The last time I used a smaller tip was because some 0402 component was too near to another so I would always have touched both.
Simon Spiers : Good repair job, its a great feeling isn't it?
I have just repaired one of these that Agilent regarded as BER. Mine had errors 612 613 618 and 619 all regarding possible U102 resistor divider. It also was dead on the 10V range DC. R122 a 6.19K was open , as was one series smt inductor in series with one of the relays.
Although I find the menus hard to navigate and the displays fade with age, they have great long term stability.
KC Micro Tronix Randall Pallesen : Great repair! I love this model meter. I have one of these on my bench I purchased broken on eBay and I love it. I will never go back to a hand held meter.
Julian 1 : Great job! That dental tool works a treat. Quick question - when desoldering the chip, you added flux, then used more solder to better distribute the iron's heat across all pins?
MindFlareRetro : Late finding this video, but I thought it was a fine repair and great info as I am looking at purchasing one with similar error codes. Well done.

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