Is there a replacement cassette mechanism assembly available for a JVC
"Have you changed all of the belts yet with new ones? I would suspect that there is a slipping belt that has not allowed the mechanism to get to a known position. Change all of the belts following the service manual to route them correctly and try again. Report here your results. I doubt that the part is broken (although there is a slight possibility). I believe that the mechanism is “out of timing” and just needs to get back in sync. If the new belts fail to resolve this, update this note and I’ll investigate further.