Hi all,
I visited a local garage sale yesterday and picked up three Keithley 199 multimeters. Of the three, one appears to operate perfectly. While none of them have probably seen the inside of a cal lab in forever, it appears pretty spot on compared to my 34410a (which is in cal).
The second one displays UNCAL on power-up, and then after pressing any button it resumes normal operation. According to the manual this is expected behavior if there is a problem reading from the EEPROM in which calibration constants are stored. Searching here and elsewhere I found a couple of threads that indicate this is a not too uncommon problem, and a bad PROM is likely. I have a few questions:
1. Can anyone tell me which PROM I need?. The manual shows a part of 2816a and I was able to see that the chip in the second unit was a Xicor X2816AP, but there's no indication of the speed, and there appear to be a few choices on eBay (the only place I've found these). I don't know if it will matter for this case but want to make sure. This appears to also be made by Samsung or Intel, is there a preferred manufacturer?
2. If it can't read the calibration constants, what values does it use? After resuming operation it appears to function pretty well. I tested DC voltage, current and resistance and while maybe not bang-on, it agrees pretty well with my Agilent meter.
3. Is there a way to save calibration without actually calibrating it before I attempt to replace the PROM? I simply don't have the equipment or ability to calibrate it and I'm afraid I'll make it worse. As it stands now it is at least usable after the annoyance of the UNCAL message on startup.
As for the third meter, it also exhibits the UNCAL issue, but beyond that it does not seem to function. It displays overload for most ranges and functions. It's unlikely that I would ever purchase a needed piece of equipment that is for parts or repair, simply because my skill level is not adequate. In this case, though, it might be a fun and educational experience to try to fix it so I will attempt that at some point.
Thanks in advance for any information you can provide.