Question about liftmaster Chamberlain Garage Door Opener Transmitter 300MC

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Garage door won't close

The door will open when you push the wall button but when you try to close it - it reverses, reopens and the light flashes 4 times. There is no obstruction (leaves, cob web, etc), the sensors are working and properly aligned and the door looks to be manually closing well. It is a GarageMaster 1/3 hp, which I understand is made by Chamberlain, and came with the house I bought so I don't have a manual and is probably about 12 years old. I appreciate any responses....Thanks Dee

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SAME AS ABOVE... AND IF ISNT WORKING TRY TO INCREASE THE DOWN FORCE OF THE GARAGE OPENER 1/4 TURN UNTIL CAN CLOSE IT... AND IF ISNT WORKING STILL MAYBE UR TORSION SPRING OF UR GARAGE DOOR HAS TOO MANY TURNS.. CALL A TECHNICIAN!

Posted on Mar 09, 2009

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Check if there is a shadow being cast onto one of the sensors as the door closes. We've had the rope for manually closing the door cast a shadow in full sun and trigger the "something crossed the beam" safety reverse. (Our temporary solution was to cast a shadow that remained constant from outside the door.)

Similarly check if there are any weeds or grass that are being blown or bent into the opening as the door closes. If there are plants in or near the doorway, trim them or use an herbicide to kill them and then trim the top growth after the plant dies.

Posted on Mar 03, 2009

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