If you are observing the waveform on the motor pins, said crappiness may easily be the result of an open circuit there. The motor itself is just a hunk of wire wrapped around a stator made of iron -- not much to go wrong electrically except a broken wire. That's easy to have happen during a gear replacement.

Replacing the motor is dicey because it is located (and somewhat secured) to the circuit board by plastic pins which are then melted over in production. It is a nice challenge for the education but not a practical service procedure, with the supply of junkyard parts still available.
--
Art Benstein near Baltimore

She criticized my apartment, so I knocked her flat.