Did your door stop working in the up position. If so, the trolley (the thing the door is connected to) is probably jammed against a bolt just in front of the motor unit. Remove the bolt and run the door down. You will find an adjustment on the side of the motor unit called the 'up limit'. Using a small screwdriver, turn this 4 or 5 turns in the opposite direction of the arrow printed on the cover. Remember the replace the bolt. Post back if you have other problems.

We have a craftsman Model 139.53978SRT1 i/2 HP. The previous owner did not leave keyless entry password or key to door handle. Can I re-program or do I need to call service person.

On the rear of your motor unit near where all those white wires go you will find the smart/learn button. Press and immediately release that and walk over to your keypad and input any 4 digit number and then press enter. Should do it for you.