Sharkfin Help!

[Kinski]

Sharkfin recently stopped working correctly. Its as though the filter wont open. Sounds as though its stuck in the dark murky closed filter. If i touch certain parts of the board I can get the filter to open up and sweep as i adjust my finger contact. So I think the filter works, its perhaps just the envelope circuit?

I replaced all ICs and 3906 with no improvement. Any ideas where to start?

I'd greatly appreciate the help!