Video Blog 185/186 - HP 3458A 8.5 Digit Multimeter Repair - Part 1 & 2

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Published: Saturday, 06 June 2026

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DISCLAIMER: This video is educational only, so if you decide to do the same yourself then you are on your own, I can't be held responsible for any problems/issues/damage/injury that may occur if you decide to follow this blog and try it yourself.

VIDEO BLOG

I acquired a faulty 3458A quite cheap in order to try out an A3 board U180 replacement (called the NU180) which fixes catastrophic & expensive drift problems on these meters.
But, does this unit exhibit the fault I was hoping for, or something completely different? Plus, there's plenty other repairs to be made along the way.

Calram and settings ram programming:
Calram: Seems that quite a few people are misunderstanding the FM16W08 adaptor board that I have produced, i.e. how to use it.
- Plug your FM16W08 on it's board into my adaptor board (your 24pin 16W08 board into the 24pin socket on my adaptor)
- Plug my adaptor board into your programmer (using the 28pin header)
- Set the device to FM16W08 (not Dallas 1220Y.....!)
- Set the end address to 07FF (mega important because the top 2 address lines on the FM16W08 board are tied low)
- Hit Program.....done.
Note: The top 2 address lines are tied low because the FM16W08 is 64kbits (8Kx8), whilst the Dallas 1220Y is only 16kbits (2Kx8).
See the Part 2 video below where I show this @ 12:58.

YouTube Video - Part 1:

YouTube Video - Part 2: