Keithley 230 repair help

[ZhuraYuk]

The problem is that some positive +1.7V offset is constantly present at the output. For example when I set +1V in the output it is actually a +2.7V, same for 100V range. When output is enabled power supply lines -+15 are also shifted to +16.7 and -12.8V. Same happening on negative range. After measuring some voltages I suspect that problem is in U309 op amp which feeds U313 LM339 sense amplifier. It should be 5V in inputs 2,3 but it is +16 and -12V instead. So far do not know what next step should be performed.

[Kleinstein]

U309 should not be a LM339 (4 x comparator), but an OP in a 8 pin case.
It could still be worth looking at the outputs of U313 (LM339) that is used to control the JFET switches. There my be one stuck on.
The circuit uses several different grounds. One has to be careful which ground is used when measuring voltages.

[opa627bm]

check the back side,
there is a switch for remote/internal sense
cycle it couple times, if still present, try to move it to internal sense and move the toggle switch handle slightly back and forth to see if you can get normal reading.

[ZhuraYuk]

check the back side,
there is a switch for remote/internal sense
cycle it couple times, if still present, try to move it to internal sense and move the toggle switch handle slightly back and forth to see if you can get normal reading.

Thank you mate! That fixed the problem, after pressing switch a little to the bottom unit works flawlessly.

[opa627bm]

No Problem, I had to replace mine :
DIGI:450-1316-ND