I detest Mitsubishi decks, always crappy.
Mechanical issues like that can be related to gears, belts (rubbers, bands). Sometimes motor is shot, also a weak fail point on JVCs.
Without service manual, no clue. Another problem is that Mitsu decks had low production, not popular, info sparse at times. You may be SOL for official repair docs. But most brands had semi-universal codes, another Mitsu model manual may always show what '3' means.
Sometimes stuff isn't covered in any manuals. I had this issue with a Dell laptop recently, light combo not covered. I read other manuals, guessed issues correctly, unit now works well.
Welcome to my world.
Few others here too, so welcome to our world!
Having fun yet?
This is why DIY repair, DIY refurb, is a PITA. You spend all your time making gear work, not using it. Your videos will never get transferred that way. Just something to remember. <<< This is addressed to others reading along, not our dedicated OP here ... probably?