amp won't turn on

I have an old Kenwood 744 4 channel amp. Lately it's been acting up randomly introducing noise into the speakers (not alternator noise). It would then go away when I cycled the amp off/on. After this the amp started cutting out completely. There is a humming in the speakers and amp itself. When On, the power light stays off but the amp hums and gets smoking hot. I don't think it's circuit protection but a component issue. I opened it up and found nothing obvious except some heat discoloration around a 16v 3900uF cap, which I replaced but it still does the same thing. I'm thinking power transistor but there are a bunch of them. I may just get a new amp but thought I'd ask here incase anyone knows what the problem is. Any help is appreciated. Thanks.

Check for bad solder joints on the small transistors that are held to the heat sink with the spring steel clamps.  Not the output transistors, but the smaller ones mounted between the output transistors.