Electronics > Repair
HP 34401a DMM with leaking segments
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hakko:
HI! I scored on 34401A (agilent dated december 2006) it have a dead front panel vfd. It does not show any digit  :-\. The front panel have a EE80C51BH 34401-88813 REV 2.0 and HV518PJ vfd driver. The meter respond for key press.
Investigating the problem I had decoded the the data from the main board cpu to front panel with a logic analizer the data will be attached here. I also decoded the serial bus from 80C51  ---> HV518 and it have clock and data activity also latch pulse signal and  strobe are always at 0 state. I think the mcu is fine but it have a dead vfd driver. The board have no shorts or huge heat elements (checked with thermal camera).
I removed the vfd driver and applied +18V (with current limit resistor) on plate and anode segments for a short time and the vfd segments light up so the vfd display it's not faulty  :)
Anyone with this board rev 66522 had this problem before? I ordered HV518 from utsource but I don't know if it's good quality  :-//
coromonadalix:
the hv518 can be ordered here

https://www.digikey.com/number/en/microchip-technology/150/HV518/114088
hakko:
But the shipment is 40$ for a 5$ part  :P
coromonadalix:
Damn   in my location, its nothing

But for Brazil  its expensive, just checked :(

An complete 34401a  pn 34401-66522    board+vfd included  is around 200$ usd  from Keysight, and they dont have tons of them left ...

And you cant swap them with an older version of the pcb, the meter FW  wont allow it.

service note : 34401A-06


My curiosity would be :   retrograde the firmware and try the older display pcb with the unobtanium drivers ??
hakko:

--- Quote from: coromonadalix on September 08, 2019, 03:13:11 pm ---Damn   in my location, its nothing

But for Brazil  its expensive, just checked :(

An complete 34401a  pn 34401-66522    board+vfd included  is around 200$ usd  from Keysight, and they dont have tons of them left ...

And you cant swap them with an older version of the pcb, the meter FW  wont allow it.

service note : 34401A-06


My curiosity would be :   retrograde the firmware and try the older display pcb with the unobtanium drivers ??

--- End quote ---

It might work with old firmware but i don't know if the meter will work fine since newer main boards have also hw changes from the old ones specially in analog section I don't know if asics are also changed too.
HV518 is also used by arduino guys I think china ones will work since it's quite usual ic.
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