Keithley 617 Electrometer faulty behavior

[matthuszagh]

I tried washing the motherboard again (this time focusing on the backside) and I don't see much difference. The leakage is now sitting at around -540fA. I may try the suggestion of looking for leaky chips by applying a bit of heat to various components, but then again I may just return it since I paid for a working unit.

I think, you mean the smaller board with the shielded preamplifier and where the the input is connected to, correct? The board where the 100R resistor is located, is not really critical regarding leakage.

I actually don't. I was of course aware that the electrometer board is very leakage sensitive, but the manual also says to watch out for the ranging amplifier section of the motherboard. From 7.9 Handling and Cleaning:

In particular, there are two areas within the Model 617 that have numerous high impedance nodes where contamination could cause degraded performance. These include the input amplifier area on the electrometer board and the ranging amplifier section location on the mother board.

Maybe that's overstated a bit, I haven't had much time to look at the schematic yet, but since the 100ohm resistor is near that ranging amplifier section that was my reason for washing the motherboard. I steered clear of the electrometer board since I didn't want to make anything worse. If I keep this unit I may look into washing that at some point.