This may NOT be helpful advise, so I apologise in advance if it isn't. This type of hardware failure is what made me pretty much give up on classic Amiga hardware for myself. Lately I only use Amiga Forever in conjunction with a Catweasel MK4. The nice thing about AF, it is just about any hardware configuration you need and it is the FASTEST Amiga compatible possible fore modern stuff.
As for your specific hardware problems, wish I could help. The only thing I can think of off the top of my head is the old open her up and reseat all custom chips. Worth a shot.
