ComparisonThe boards have the same part numbers, and I did not notice any difference between the PCBs apart from ROM versions. Feel free to study the pictures and see if I missed anything. I was expecting maybe a jumper to be different, a beefed up power supply, or some extra traces ran to the scanner.
The Keithley 2000-20 identifies itself like any other unit via GPIB, no change in the model number:
KEITHLEY INSTRUMENTS INC.,MODEL 2000,0698950,A08 /A02In no way that I can see does the unit identify itself differently. A superficial glance at the EEPROM differences looks like the differences just concern different calibration constants, serial number and checksum, although it's definitely possible that there is a flag in there somewhere:
So right now it looks to me like the
-20 designation was just to identify the unit as bundled with a scanner card. Somewhat similar to how Tektronix had the
AM503S, which was just a bundle of a TM502A mainframe, AM503 amplifier plugin and storage drawer plugin. It may be that only certain firmware versions support the 2000-SCAN-20.
Let me know if there's anything else you want me to check. Probably in a couple of days, the Keithley 2000-20 will go back in the stack, and will be much more of a hassle to get out.
My suggestions for trying to use a 20 channel scanner in a standard Keithley 2000 would be to first test if it just works, if not, try using the A08 firmware that I attached, and if that still does not work, maybe try loading the EEPROM dump I uploaded, with the obvious caveat that it will mess up your calibration and serial number, so better make a backup first. If the EEPROM replacement works, then it might be worth trying to isolate which byte is causing the difference.