Definitely worth working in...
I have bought three (one incomplete) 8502's at an hamfest, let them acquire some dust before opening them...
First thing: You'll definitely need the service manual. Some guys sell Fluke manual collection CD's on FleaBay..
These multimeters are pure FLUKE. Extremely well built !!!!
Some weird design though... The DC conditioner (DC volts input) has a BIPOLAR input !!! (No FETs)
Probably that, back in 1978, BJT's were better than JFETs for matching/nulling... but what's singular is that the input diff pair is emitter-biased by a 1 MEG resistor and a "bias" adjust sends a nulling voltage to the input via a 100 MEG resistor !!!
But FLUKE didn't neglect JFETs at all... they're everywhere... as analog switches.
The ADC is a "Fast RR ADC" (RR for Recirculating Remainder) is kinda weird, but it is working !!! I still have some reading to do...
Important: Keep your screwdriver far from the trimpots until you fully understand their purpose. ESPECIALLY the Fast RR ADC module. Some of them are in the heart of the Fast RR thing. You do NOT want to to tweak them!!!
First thing first, remove the power supply and test it. (Power switch comes with it). Hold the supply by the main transformer, not the heatsink. The 90° fixations / PCB will flex, possibly damaging the three Controller regulators on the heatsink.
The Power supply has two distinct output sections: Guarded (for analog sections) and Unguarded for logic/controller. The Power switch and largest capacitor are in in the Unguaded section.
Three supplies (+30V, -30V and Logic return, all in the Guarded section) are ladder-mounted on other (guarded) supplies.
Particularly, the Guarded 5v2 supply positive is ladder-mounted on the -15 Volts, hence, the Logic return (5v2 negative) will read -20.2 Volts.
Trimpots:
- R9 for +15V,
- R5 for floating 5v2 guarded supply
- R6 for unguarded 5 volt supply.
Be careful if you remove the power supply. The main power transformer fragile windings are directly soldered to the PCB.
Then, the first range you want to test is the 10v DC volts range. In it, the DC conditioner's attenuator is not used and the amplifier has unity gain.
For vintage processor lovers, the 8502 controller uses a genuine Intel 8080 !!!!!!
BTW, the FLUKE 7600 is a copycat of the 8502 (or reciprocal

)
73 de Normand VE2UM
More news later...