More low leakage porn - Keythley 485 Picoammeter Teardown

[mimmus78]

I brought this meter a year ago for 50 EUR and the baja, after putting back the mains cord I was surprised I was able to turn it on and test good the upper ranges.
Didn't made extensive tests because I was very busy at that time and unfortunately I decided to not go further my battery powered projects so the meter was
sitting unpowered on the shelf up to today.

Today I wanted to use it to check some capacitor leakage but it turn out the most of the ranges do not work correctly.
As any old equipment of this age this meter is very simple to debug, the instruction manual explain exactly how it works and has a debug/test procedure that you
can activate to check all relay and switches on the analogue circuit.
After 1h on the bench it turn out there is a leaking analogue switch (I don't know you guys but I always get this analogue switched failure with my equipment).

I noticed also that it seems there are no images of the internal of this instrument so I decided to fill up it today.

I will let you know when the switches arrives the rest of the story ...