Take a look, but sounds like the pinch roller is not making good contact with the capstan.
Is it playing tapes fine? If it ain't broke don't fix it!
Ignore my send line...I see it's not playing tapes.
I just went through a whole troubleshooting on my JVC 550 deck. There is a wealth of knowledge on here and if you spend some time, you will narrow it down, and learn a lot in the process.
I'd start with cleaning the rubber tires (pinch roller / idlers). Clean the capstan.