Replace those dreadful AF116 (or AF117) transistors, one or more will have
internal shorts from the screened metal can to one or more of the internal
junctions or leads.
Tapping them with a pencil or similar will sometimes produce a brief burst of life
and it may even live up and work normally again - but only for a short time.
AF179 is a great replacement. A bit costly but you only need a few and it actually
gives much better results than the original ones, even from new.
It's only a three-pin component so forget about the screen pin.
Martin