Used keithley 2602 SMU misbehaving

[bitter_mike]

Hey all,

I'm hoping for some advice tracking down a problem with a used Keithley 2602 dual SMU that I have. The second channel ("Source B") works perfectly: you set it to 5.0000V, it puts out 5.0000V, and correctly measures it's own output as 5.0000V. The first channel ("Source A") is the misbehaving one. It's not regulating its output correctly. If I set it to 5.0000V, it puts out around 5.2V, and that output drifts up quite a bit if I let it sit there, like 10s of mV over the course of a few minutes. This is in comparison to Source B, which is rock steady. Source A is correctly measuring that it's putting out 5.2V or whatever it is, it just won't put out what I tell it to.

I'm not particularly experienced in repair of something as complex as this, so I'm hoping someone has a little more experience with this unit than I do. It was really cheap and its sooooo close to working perfectly and I'd like to get it there.

Appreciate any help.