My older Genie Pro 88 started a new failure symptom the other day. At first, the door would travel to near bottom, then stop and go no further. Now it starts, travels 6" or so, and returns to the starting point. This unit does not have an interrupter cup and RPM sensor that I can see. It has instead a coil that appears to sense the drive motor rotation from cams on the back of the motor. The coil measures 120 ohms, seems good. Any garage door Genie-experienced guys out there? Thanks.