What next? How can ohms be perfect and all other ranges (I also tested DC current and Diode check) be off by more than a factor of 2?
As noted, this thing has a chip-on-board IC – unmarked – for the A/D and display driver and custom Beckman parts for key resistor networks. Thus, it is virtually impossible to determine any circuit details (not to mention the 32 pole rotary selector which cannot be used with the unit disassembled for testing). There is one pot – full scale adjust – which has about a 10 % range end-to-end and affects everything but resistance. Perhaps, resistance is calculated by performing a comparison with a known resistance. Then, they would both be off by the same amount. Maybe I could bugger this pot to drop it down but I would really like to determine the root cause. Modifying the adjustment pot circuit turns out to be impossible since it is connected to the above mentioned unidentified resistor networks and any attempt would be a shot in the dark. So, now it works fine as long as I multiply all my (non-resistance) readings by about .4. I thought I was able to ‘fix’ DC volts by installing a 1.3 M
