It might also be a problem with the motor control electronics. I 've had two that would randomly start spinning at about 200rpm and the problem were on the PCB that drives the motor. Check it for dry joints and if this doesn't help, replace the electrolytic capacitors on it.
Don't give up until you have tried replacing every electrolytic capacitor on the circuit board. Most of them are of commonly available values and are cheap to buy. If that doesn't work, the UPC1003 integrated circuit (made by Matsushita) is toast. Unfortunately replacements are extremely hard to find.