Hello all. I have a newly acquired Keithley 192 meter that has an issue with the DC volts function. I am just starting the troubleshooting process, so bear in mind I'm still sorting...
Software version: E7
The meter has the 1923 IEEE-466 Interface option, but no AC Volt option.
The self test (program eight) passes the Display, Ram and Rom test. I have tested power supply voltages and all are within spec. All front panel functions/buttons work and select the functions as they should. I just realized I have not done a ripple test though...
So - the issue. Firstly, the Ohms functions work okay. I have not checked for accuracy, but my sampling of precision resistors indicate it's not far off. However the DC Volts function is not working. Measuring a battery shows no indication or change. Zeroing the meter on ohms works. Zeroing the meter on DCV works, but even with leads shorted it climbs from zero rather quickly and then jumps all over. I think an indication that there is imposed DC somewhere is that at .2 and 2 settings, the meter reads OVLD. Above that it indicates random voltages - not wildly random, but jumping around.
I'm just digging in to the service manual and the tests they outline, but wanted to bounce this off you folks to see if there are any general issues with this model to look for. A little reading may have me start at the Mux Fet (Q328) and the protection Fets (Q329, Q330)?
Thanks - Mark