On Tue, 3 Nov 2009 08:46:16 -0600, "pacca" wrote:

I have lift-master garage door opener , at times when I close the door it
will reverse it self when it reaches the bottom , it's a chain drive 1/2
horse opener, any body have had this problem.Thanks

Check the photo cells for proper alignment and clean the lenses.

Next would be adjusting up/down force settings.