[time-nuts] Data Precision 8200 Voltage Standard

[Skip Withrow]

Realize a voltage standard post might be a little off-topic, but have seen 
them discussed quite a bit, so here goes. 

We have a Data Precision 6-1/2 digit voltage and current standard, which 
seems to operate except for the function of the front panel voltage 
selection.  The mode and +/- voltage switch work fine.  We do have the 
service manual, and the switches are read by the microprocessor.  After 
checking the signals associated with the switches (read signals are 
generated by the uP, and read back on the data bus) my best guess is the the 
uP code my not be working correctly. 

The processor in this unit is a ROMed R6500/1 (cousin of the 6502).  I fear 
that perhaps a bit in the ROM is being read incorrectly (in the switch read 
routine).  My guess is that there is no way to read the code out of this 
part. 

If any time nuts have a parts unit laying around I would like to try 
swapping the processor to confirm my theory.  My next check will be to 
adjust Vcc up and down and take some freeze spray to the processor to see if 
I can find a point that it will operate, however, that will certainly not 
provide a fix. 

Any help appreciated. 

Skip Withrow