Did you ever fix this? I have a Beocord 3500 that’s playing, but not rewinding or forwarding. Seems to be a similar problem. Mine is a type1 deck with only one belt. I am suspecting the belt as well, since it’s a bit loose.
I’ve checked voltages, manually checked the solenoids, signals for forward and rewind. It all seems to work from an electronic perspective.
When I put a tape in it, it won’t even forward or rewind, but when I hold the cassette detection switch it does for two to three seconds. That’s when the tape detection sensor kicks in and stops and switches off the whole machine.
Thoughts anyone?