My 80's JVC cassette deck no longer switches off at the end of a tape. I found a small metal plate next to a solenoid that disengages the mechanism when pressed, so my guess is that something is failing to activate the solenoid. But beyond that, I'm stumped.
Oh, I didn't know about that. I suppose this is in the area of the heads, like most other things? Does it use a light source? I've never noticed anything like that, but I suppose it'd need to be very dark to see it.
ISTR that VHS used a light as a dew sensor. My first thought was to look for a small moulding that pushed into the tape, and detected when it got tight (I've seen such on many portable players I've owned), but I can't find any trace of one. Maybe that's why it stopped working? OTOH, I would surely have found it in the case if it had dropped off, or would be able to see the metal arm that held it.