I have a 1/2 Craftsman that is at least 7 yrs old. When I try to open it at the side door, the motor and light come on, the "trolley" thing runs down toward the door, but the door doesn't open. When I release the "open" button, the trolley runs back to the base. I notice one of the photocell sensors near the base of the board is out; however, I was having the above problem when it was on. I can't find the manual either online or in the files I inherited when I bought the house. I've read prior posts but can't figure out where all the parts are without the diagram.

Any suggestions? Thanks!
Alley