I picked up a misbehaving Keithley 2400 SMU for
$??? "a very good price".
It will output accurate (but noisy) voltages under 20 V, but goes into OVP mode at anything above that, regardless of OVP settings. The current measurement is bonkers. It shows a high offset and reads several times the actual current. I opened it up and eventually found that a comparator is missing along with a couple of pads/tracks leading to it (bad removal job by some previous owner). I'll replace that then go from there. It won't be trivial as one of the missing pads leads to a via under the IC
. It's not the only fault I'm sure. The service manual is a complete joke, and there are no helpful built-in tests like the 200x meters have. No troubleshooting info except for a few voltage checks, and even for those, there is no additional information, e.g. what this signal is, where it is sourced, what it drives. Nothing
At least the service manual has a parts list (about the only useful thing in there) so that I could identify the missing IC. The VFD is perfect, better than any of my other Keithley gear. Even broken, this is probably worth many times what I paid, so it qualifies as a "score". If nothing else, it will be a fun spare time fixit project.