Sears Craftsman garage door opener
It's worked fine for a long time, but tonight the chain slipped off. I managed to get the chain reattached and in what I think is the proper position, and tightened it a bit to reduce the sag. The door is down and the latch is sitting right behind the sleeve (correct terms??) waiting to slide into the locked position when the door raises.
When I activate with the remote, the motor pushes the door further closed, bowing the track quite a bit....then it backs up about a foot before shutting down. It almost seems that it's running backwards and shutting off when it reaches the pressure limit, however the chain is on the proper side.
I do have the book....I cannot figure out where it is at the moment. This is 15 year-old 1/2 HP unit.
Any ideas would be appreciated, at the door opener is also the only real means of locking the door closed.