Robert, all I needed was "Rock-Ola" and "gripper motor" -they are
notorious for developing shorted armature turns. From the early
1950's models, right on through the later 80's. If it is blowing
quickly, that is the cause.

The only other possible cause is that the cam switches are faulty and
causing the motor to overtravel and jam. That will be obvious when
you turn the motor shaft.

Rob/NYC