Victor QL-Y77F motor speed unstable

I have a Victor QL-Y77F turntable that one day started to miss the speed lock.  Even when the motor is in stop mode, the platter still rotates a little bit (random actually) backwards.  When is in START mode (33 or45rpms) the speed randomly jumps from green to red and back, meaning from stable to unstable.
I tried to replace the Crystal and then the Hall generators but with no luck.  Actually without the service manual is pretty difficult.  Do you have any ideas what to do further?

TIA
Corneliu