Electronics > Repair

HP 34401a DMM with leaking segments

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coromonadalix:
normally they are compatible for both

its the same glass ...  but different drivers ...   :-+

lucky for us the design leaked and was copied ....

amp:
I just finished this modification to my HP34401A as my DMM also had an issue with leaking segments.

For the connections to the OLED DISPLAY MOD PCB by QU1CK:
- GND (W601-P1 = GND)
- VCC (W601-P3 = +18V) I read in this thread that sourcing the voltage from VCC (generated by U553) could be better so this could be checked. If you do this, you need to make a connection to the main PCB.
- SI    (W601-P2 = FPDO)
- SO (W601-P6 = IGFPDI)
- SCK (W601-P4 = IGFPSCK)
- INT (W601-P10 = IGFPINT)
All connections soldered in parallel to the 12pin ribbon cable on the front panel PCB. (Reference names added above are from the HP34401A service manual
 
I used the firmware_nobootloader.bin (v1.1). This was directly flashed to the STM32 by temporarily connecting my programmer to the SWD interface and programming the binary at address 0x08000000.

I thought of just sharing the information regarding the pin connections as it could help someone else who wants to implement the mod.

Thanks QU1CK for this mod.

mawyatt:

--- Quote from: gamerpaddy on October 31, 2024, 10:12:43 pm ---For me it did, yes.
the front panel pcb were different
one contained a big dip NEC job
the other one two four sided ic's

--- End quote ---

Just replaced the display in our old HP34401A with Red Terminals (has NEC DIP). Not having the proper desoldering tool (just wick and the cheap hand plunger) we opted for a Yihua 929D-V.

The replacement display was from AliX and slightly different than the OEM, but we had little trouble replacing the fading OEM one.

https://www.aliexpress.us/item/3256806057902868.html?spm=a2g0o.order_list.order_list_main.23.7380194dxSFr2T&gatewayAdapt=glo2usa

The Yihua made quick and easy work of removing the old display and left the PCB is good shape!!

Anyway, thanks for the info and as you can see these replacement displays work with the older Red Terminal HP34401A.

Best

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