As I said in post #650 of February 13, 2019, I have an 8100B that read slightly high. I was able to bring it spot-on with a slight tweak to R175 ZERO. I'm still curious about the other ADC adjustments (R308 TRIP POINT, R149 REMAINDER), but it's pretty useful as is.
I don't see a separate thread for differential voltmeters, so I'll say here that I just got a tube-type 825A/AG back on its feet.
This model is a premium version of the 801B with a 1mV null detector vs 10mV. The /AG means the reference is a Zener instead of a standard cell.
Unusual cap failures: a leaky electrolytic that depressed a regulator, another leaky electro coupling cap causing null detector offset, and an electro that was pretending to be a battery. I rarely see a leaky low-voltage electrolytic that causes a malfunction, usually they just dry out.
Unusual cap, that failed: Why did Fluke use a paper/oil bumblebee? In a sensitive spot in the regulator? While the rest of the film caps are mylar?
Also a rectifier with photodiode action causing more-than-full-scale offset on the recorder output.
When I accidentally applied high voltage on a low range, one of the polystyrene input filter caps gave its life to protect the neon that was supposed to protect it. But after one hour in total darkness, the neon fired at 92V so it just must have been the cap's time to go. Not having a 0.1uF polystyrene, I used polypropylene.
The plastic number wheels were warped causing them to rub one another making the action rough. This probably afflicts the 801B and other models that use them. I fabricated good-looking replacements using the original metal hub, a cut-down CD blank, legend overlay designed in LibreOffice Draw, and self-stick plastic laminating sheet. They look great, and the knobs slip from one detent to the next with that smooth ringing clank like they're supposed to. I'll post the recipe if anyone wants.
The switch contacts were dirty, but they quieted after a shot of polyphenyl ether.
I was beginning to compare it to my gold standard 895A when the latter failed. Not my favorite scenario.
But it turned out to be simple, just an open electrolytic in the 1100V Reference Supply, parts are on order. Four Nichicon UCA-6 (short and wide) 22/450.
It's been a good week.
Dave Wise