Keithly 227 On the bench for repair.

[Zenwizard]

I have a keithley 227 current source on the bench for repair. It seems to 1/2 way work but it will not output any voltage or current.

I have verified the VS + and - 12 as well as the VD + and - 12 the high voltage is present as well. The odd part is when the meter is in current measure mode it is working and the meter will deflect. When it is in voltage measurement mode there is no meter deflection. Looking forward to adding this one to the lab if I can get it up and running.

Anyone worked on these that might have a good starting point?

Zen

[Zenwizard]

I think I have this one figured out. U205 is getting control and being told what to do but its output is stuck and will not move. Unfortunatly in the 227 U205 is a custom Keithley part and is just labeled IC -76. So there is not a lot that will be able to be done to fix the 227.

Zen

[tppc]

As per the 227 service manual, U205-IC76 has the same pinout as LM318.
The original Keithley part is probably a selected opamp with better carateristics, but at least for the repair, I believe you can try with a regular LM318.

Regards.

[ch_scr]

It's already broken, might as well desolder that OPA and try to find a replacement.