Liftmaster 41A5021-4M-315 Receiver Logic Circuit Board Assembly (315 MHz) Opener. Liftmaster & Chamberlain Replacement Garage Door Opener Parts.
- Place a one inch board, or 2x4, under the center of door with the door fully open.
- Close the door. The door should immediately reverse directions when the garage door hits the board.
- If the door only stops on the board, instead of reversing directions, increase the Down limit by turning the adjustment screw 1/4 counterclockwise.