Liftmaster 3500D Randomly Reverses at Bottom


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Old 09-15-12, 10:42 AM
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Cool Liftmaster 3500D Randomly Reverses at Bottom

My Liftmaster 3500D has worked fine for 6 years. Recently it has started reversing just as it stops in the closed position. I've reset the limit stops and the force several times but it still randomly opens at the bottom of travel. It's always in the same place - just as it stops at the bottom travel. I've cleaned and checked the safety sensors also. Any ideas?
 
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Old 09-15-12, 10:59 AM
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P.S. Just had it happen again. I let the door open all the way. The LED on the unit now blinks 11 times, but I can't find anything in the Owner's Manual to tell me what the code means.
 
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Old 09-15-12, 11:11 AM
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See the following, which is your manual, under "having a problem" and section 10. It describes the reversing and the lights flashing for 5 seconds afterwards. Maybe it will help. http://www.davesgaragedoors.com/imag...er%203500D.pdf
 
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Old 09-15-12, 01:48 PM
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If the lights on the motor flash when the door opens its the sensors. Sometimes they seem like they are aligned but are not lined up right. The amber light on the sending sensor should always be on. The green light on the receiving sensor is the one you should really concentrate on. Grab the green sensor with two fingers and wiggle it lightly. If you see the green light flickering, just loosen the wing nut on it and try to align it better. Also make sure that there is nothing that is hanging from the bottom of the door that may trip the sensors. As the door is closing look at the green sensor and make sure it stays on the whole way down.
 
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Old 09-15-12, 01:52 PM
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You may also have the limits set too far on the down position.
 
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Old 09-16-12, 08:39 AM
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Question

I've tried adjusting the limits using both the manual and automatic process. When I did it manually, I set the bottom limit slightly open, but just closed enough that the seal on the bottom of the door was barely touching the ground.

As far as the sensors go, I tried a slight reposition, but even before I adjusted them both the yellow (send) and green (receive) lights stayed on throughout the operation.

I also lubricated all of the hinges and rollers, and checked the tracks. I moved the door manually and there does not appear to be any binding.
 
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Old 09-17-12, 06:07 AM
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Do you have one or two learn buttons on the back of the motor?
 
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Old 09-17-12, 10:53 AM
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Two buttons. (I have to add more verbiage to meet the forums requirement to have at least 25 letters, so ignore this.)
 
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Old 09-25-12, 07:39 PM
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As elalvaro said you really have to pay close attention the sensor with the green LED, sometimes if the adjustment of the eyes are close to their "margin of play" meaning right on the edge of their working adjustment, the door reaching the down position and flexing the tracks even a 1/4" will cause the green light to flicker and reverse the operation. Easy diagnosis:If after the door reverses and opens back up the light bulbs in the actual machine flash, its an eye problem. If the door hits the floor, and the motor keeps pushing until the door reverses and the light bulbs in the machine stay solid, its a limit issue. Try holding the wall control button down continuously until the door closes all the way, if it stays closed than the eyes are the culprit.
Try adjusting the eyes so that there is about an inch or more of play before the green light goes off
 
 

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