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WTB: Drifty A3 (ADC) board from 3458A

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TheSteve:
I'm looking for an A3 ADC board from a 3458A that has excessive drift - I don't care how bad the drift is but I'd prefer one that is not generating any kind of fault.
This is for testing a "cure" to the problem.

Shipping to US or Canada.

coromonadalix:
You do know it can cost up to 1k$$ for a good one ??  EDIT   for a drifty one    ???  no idea  sorry


Related threads about the A3  board

https://www.eevblog.com/forum/metrology/hp-3458a-ad-board-spare-part-availibilty-and-cost/

TheSteve:
Yep, I need a bad board to further test a possible fix for the drift.
You can no longer purchase new or refurb A3 boards from Keysight.

Kleinstein:
TiN did quite some tests and tries to fix it with his 1st bad ADC board. The conclusion was that the resistors in the ASCIC somehow started to dirft a bit. Not all resistors are acessible externally and replacing the ASIC completely can be tricky - there are switches with a difined ratio in the switch resistance. It is a bit more complicated than just multiple equal resistance switches. More like having 1:4:5:16 ratio in the switch resistance.

TheSteve:

--- Quote from: Kleinstein on June 15, 2021, 05:25:37 pm ---TiN did quite some tests and tries to fix it with his 1st bad ADC board. The conclusion was that the resistors in the ASCIC somehow started to dirft a bit. Not all resistors are acessible externally and replacing the ASIC completely can be tricky - there are switches with a difined ratio in the switch resistance. It is a bit more complicated than just multiple equal resistance switches. More like having 1:4:5:16 ratio in the switch resistance.

--- End quote ---

Yep, they are a bit of mystery. I have an A3 that was drifting at 0.4 to 0.8 ppm/day. After a bit of a "fix" it is now ~ 0.02 ppm/day. Could be a total fluke, maybe it won't last. I just want another board to try the process on.

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