Fluke 931B repair

[Rax]

As one's splendid "sub-ppm" levels calibration/hobby lab goes, once you think you've figured your 8 1/2 digit measurement on your calibrator calibration, your ACV differential meter poops out.

My 931Bs "fourth digit" doesn't want to adjust smoothly and I suspect R37 is not tracking well. It's a hermetic pot. I wonder if anyone has run into similar issues and figured out a solution. Other than getting a replacement - and I assume throwing out its cal/adjustment - I can only think of poking a hole and spraying some Deoxit in there (it's a ww, so no reason for FaderLube), and letting it dry. Then working it and hope it's smooth like a baby's buzzum.

The other issue is the mechanical dial is not quite going from 00 to 100... And yes, I absolutely want to keep the calibration untouched!

How would you tackle this?

[m k]

Why R37 and not the angle gear?

[Rax]

Why R37 and not the angle gear?

I don't think I'm getting mechanical slippage - the symptom is I sometimes don't get progressive, expected activity from the meter upon adjusting (I don't get any activity) - but it's a great question, I should probably take a closer look at that.

When it's behaving "expectedly," I seem to get measurements that are scary close to what I expect, given what seems a pretty simple design for an ACV instrument.