I used to work extensively on these. Your transport is not frozen -- the motor is supposed to be locked when the film is not moving to prevent sync from slipping. It just thinks that the transport is stopped all the time.
To troubleshoot, exchange the cards between transports. If the problem stays with the transport, then you know that there is a problem with the transport itself or the controls. If the problem changes to the other transport when you exchange the cards, then you know that the electronics card is bad. It is a good idea anyway to pull and re-seat all the cards -- this often cures problems by cleaning off oxidation on the contacts. Other common problems are a blown out light bulb (the tachometer on the transport motors uses two light bulbs!), and a break in the speed control knob element. The motor drivers can also go bad -- you may also be able to track this down by exchanging drivers. Check the +35v fuses too -- a blown one can indicate a shorted motor driver.
Belts sometimes are black, depending on the type of rubber they are made of.
Thanks,
Adam
