22-12-2015, 02:06 PM
(21-12-2015, 04:01 PM)ppppenguin Wrote: Decouplers are not perfect. They have stray inductance and are not truly zero impedance. It's the designer's job to select suitable components. Some circuits can be very critical about their decoupling ...
Consider instability in a TV IF strip. There are a lot of decouplers in there and, on a wired chassis, may well have been fitted first to keep the wires as short as possible for low series inductance and, therefore, difficult to get at.
Yet it is unlikely that more than one has failed - but which one?
Easy - take another suitable cap - 1nF tubular ceramic, for example - and carefully hold it across each suspect in turn. But wait - you can't have long leads if it is going to be a guaranteed successful test and the wires are closer together than the width of your thumb and finger ...
So, what's 200V between friends?
I can't claim originality for this but here is something I made well over 50 years ago to solve the problem ...
