Author Topic: WTB: Drifty A3 (ADC) board from 3458A  (Read 460 times)

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Online TheSteve

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WTB: Drifty A3 (ADC) board from 3458A
« on: June 13, 2021, 10:24:50 pm »
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.
VE7FM
 

Online coromonadalix

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Re: WTB: Drifty A3 (ADC) board from 3458A
« Reply #1 on: June 15, 2021, 10:04:16 am »
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/
« Last Edit: June 15, 2021, 02:20:44 pm by coromonadalix »
 

Online TheSteve

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Re: WTB: Drifty A3 (ADC) board from 3458A
« Reply #2 on: June 15, 2021, 05:04:56 pm »
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.
VE7FM
 

Offline Kleinstein

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Re: WTB: Drifty A3 (ADC) board from 3458A
« Reply #3 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.
 

Online TheSteve

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Re: WTB: Drifty A3 (ADC) board from 3458A
« Reply #4 on: June 15, 2021, 07:46:07 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.

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.
VE7FM
 


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