[drh4683]

If your tuner is jammed, check to see that the drive pin is not inside the starwheel. The starwheel is the large sprocket with the channel skip tabs mounted directly on the tuner shaft. Chances are grease dried and the system is extremely stiff. At one time, the motor just had barely enough to turn the gears and then stopped leaving the drive pin in the starwheel. Hopefully the motor is ok, as it is bound up with power applied to it. Ive replaced motors before because of this. You will need to manually push the pin out of the way. If that doesnt work, you need to pull the tuner, WD 40 any bushings and turn the gears, then lube with oil. WD40 will evaporate and leave the bushings dryout leaving no lube at all. You will see what Im talking about when you can see it up close.
Even when working properly, early space command sets (56-61) will turn channels rather slowly. 1962 zenith models had a redesigned space command tuner drive making the sets almost immune to mechanical failure and they also changed channels much faster.