Moscaps? Any ideas?

Protection diodes.

Cheers

Phil Hobbs

Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around. BFT25 has fA leakage... if you can get them. I could spare a few.

There's probably a common TO92 transistor with sub-pA leakage.

torsdag den 13. oktober 2022 kl. 22.52.31 UTC+2 skrev John Larkin:

Oh no! It's Squeaky Dave!

he doesn't drink, so his voice never gets lubricated ;)

A big of brake cleaner might help. ;)

Thanks for the replies. JC

There are special low-leakage diodes, just Google for 'picoampere diode'.

The best-known is called PAD-1, from several manufacturers.

I would think that if this was a Fluke designed circuit, that it wouldn't be something that wouldn't work.

The people I know that work in the Fluke calibration engineering department are pretty smart.

boB

The PADS are actually jfets. They are expensive, have crazy high capacitance and series resistance, and leakage is huge compared to a decent transistor c-b junction.

node impedance ~ 1M so

node impedance ~ 1M so

= RS

I tend to agree and as this is an expensive repair/piece of gear I think I might go with the PAD solution suggested by TV. They are easily available and not that expensive in the world of Fluke parts :) Thanks again for all the replies, much appreciated. JC