Another faulty Keithley 2100.

[Oldtestgear]

I recently acquired a Keithley 2100 that was donated to me as "very faulty". The wretched thing would power up but not do anything even though the display did change in sympathy with the button being pushed. Once in a while it would actually work for a few seconds, and then stop.

After tearing it apart & a bit of probing around I found a fault. A previous owner had changed all the supply capacitors & broken  a track that powered all the relays. A bit of rewiring & this was solved. It now works on DCV/ACV/DCI/ACI but not on continuity or resistance. The current is approx. 8-9mA on all resistance ranges &  any resistor on the 100R range is measured at about 10x the real value. At least that seems to have signs of life.
The fault seems to be in the current source but that is a far as I have got. Others appear to have similar issues & I am hoping that someone may have sketched out the circuit or provide a bit of guidance as I am now stuck.

Thanks for any suggestions.

Phil

[TiN]

2100 is not a real Keithley, so this thread might be much more useful if you squeeze some photos of innards for our common knowledge sharing.