Accurate Low Amp Current Probe Advice

[MarkL]

...
Maybe the 1uf bipolar capacitor can make a difference; I have not checked where this is at in the schematics.

The 1uF is connected to pin 8 of U171, which is the output amplifier on the AM503A schematic, and confirmed to be the same on the AM503B PCB.  The other side is GND.  Pin 8 is the variable gain input, and the 1uF is performing a filtering function for a buffered output coming from the DAC.

It's a sensitive input as it affects whatever the step gain is set to by a factor 0.5x per V (range = +/-1V).  So, a noisy input here due to an ineffective 1uF could certainly make a mess of the output.

[Martin72]

Here is an excerpt from the plan.


If the capacitor were defective or “worn out”, it would indeed be a problem.
But the ESR has nothing to do with it; it can serve as an indicator of a (beginning) deterioration if you know the correct value (data sheet).