Yup, I also believe that the motor control circuitry might be acting up. Perhaps is there someone on the forum that knows something about these three phase motor controllers, as they were used on pretty much every floppy drive. It might be a dried-up capacitor on the PCB, however, I checked them with an ESR meter and found no obvious faults.

I Googled and found this blog that someone also had acting-up floppy drive and he fixed it by replacing the hall sensor. However, there is very little other information about the diagnosing of these motors.