I installed a ***** model 139.53990 garage door opener in Jenuary, 2004. It woked for two weeks, then the beam receiving sensor failed to work (door would not close). Tested the sensors at the motor, OK. Placed back in circuit and they worked for a short while then green light on receiving sensor showed it inactive. In short, the sensor tests all right at the motor and when placed back in the circuit and properly aligned will work for a short while, then out again. What else could this be except a faulty receiving sensor?