Hi Skip:
Don't know this unit, but can comment on this kind of problem. The most
likely cause is a poor (oxidized) electrical connection. So if there
are switches, connectors, sockets, etc. involved then they need to be
cycled a few times. See What Goes Wrong:
http://www.prc68.com/I/HaT.shtml#Wgw
Another possible problem relates to electrolytic caps where the
electrolyte has gone bad. You need an Effective Series Resistance (ESR)
meter to check them, see Capacitor Failure:
http://www.prc68.com/I/HaT.shtml#CF
Have Fun,
Brooke Clarke
http://www.prc68.com
Skip Withrow wrote:
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
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