

On a high level, you can get a cleaner like Deoxit D5 in a spray bottle. Most pots have a slit in them so you can spray into them, then turn the pot through its range a bunch of times. It’s worth a try as a start. Obviously do it while the unit is unplugged.
If you want to consider a more aggressive rebuild, like a capacitor replacement, maybe find a cheap old amplifier at the thrift shop to use as practice for desoldering/resoldering.
You might be able to connect the BT to one input on the amp, like the tape input, and the CD to another.













Use MCUs that can be programmed over straight USB.