Thanks, we have a 10nF , 400V film capacitor, in circuit it has a sine on it of peak -80V to +80V......we rely on this cap for timing....near the zero cross this cap obviously has near zero volts on it, and we still rely on it being 10nF at such low voltage...i wonder if this is possible?
I looked into ferroelectric caps, and if plastic film is ferroelectric, then it may mean a kind of polarisation occurs, and maybe this messes things up near the zero cross. Still, some of the circuits work, and some dont, even though they all have the same 10nF,400V cap in them.......and sometimes the working ccts stop working, and vice versa.