What you need to do is pull the logic board from the motor unit and look for loose connections on the printed circuit board. Look closely around the small transformer. Make sure the screws are tight on the rear of the motor unit that secure those white wires. Now I am assuming that when you say "the door will go down a foot or so and then no power" that the door is just stopping at that point and not reversing to the open position. If my assumption is wrong we are looking at another problem.