Hi All,
I've got a Keithley 196 that isn't reading ohms right. They never settle (even when shorting the terminals together), and often go negative. I assume there's some leakage in the current source path, but I'm having a heck of a time figuring out what I should be looking at in the Schematic.
Anyone have any places to look? The manual talks a bit about how the ohms path works, but it's mainly "Protection on the ohms ranges is accomplisehd by RT1, Q9 and Q16. For input voltage applied to the
terminals, Q9 and Q16 clamp the voltage to the reference resistors to a safe limit. RT1 limits the current to Q9 and Q16."
The equivalent circuit shown just shows the reference resistors, which I assume isn't the issue, but rather some leakage through a FET or BJT. The second image on 5-4 may be the answer...
I've also attached hi-res schematics. Any help would be greatly appreciated!
Also, hope everyone is staying healthy! I'll admit, I'm working on this because I'm stuck at home... nevermind I have other meters in perfect working condition. Just figured this would be a good opportunity to fix this one.