curmudgeon wrote:
Had the same problem and on close inspection found that the ball
bearing hub
on the pulley attached to the spring had failed. The force then
required
was causing the motor to stop the up and down movement after a few
inches of
travel.


Good call & that would be my first guess also. With the door open, pull
the cable off of the pulleys one at a time (put vice grips under a
roller to keep the door from falling)and check to see if they spin
smoothly. If lubricating (lightweight oil) doesn't help, replace them.

Doordoc
www.DoorsAndOpeners.com