Our garage door was acting erratically for a few months. Although it would open fine, upon attempting to close, it would go up and down and the lights on our motor would flicker. Occasionally, it would refuse to stay opened. As we couldn't diagnose the problem ourselves, we called Doormaster.
Without much inspection, the technician decided that the problem must be in the motor. He replaced a capacitor and a logic board, charging us $300 for this (including labor and the service call). Fools that we were, we never asked him how he knew that these were the troublesome parts, and whether it would have been better to just chuck the 15-year old motor and install a new one.
A week later, the exact same problem returned. Turns out their "warranty" is useless and covers only the new parts put in. There is no guarantee that your problem will not recur, and you will still have to pay the exorbitant service call charge a second time.
Needless to say, we did not bother calling Doormaster again.
The problem was not with the motor all along. The chains and the motor were not correctly aligned, the garage door rollers had to be replaced, and the photo eyes at the base of the tracks were dirty and had to be cleaned.
The technician had taken advantage of our ignorance. Buyer beware.