Last night the chain on our craftsman 1/2 hp garage door opener came off the sprocket. We reattached the chain. Now the chain comes off the sprocket after 1 cycle. We used our owners manual as a guide and tightened the tension on the chain.
The way to find the problem will likely be through observation. With the opener disconnected, try opening the door manually. It should open reasonably smoothly. If there is a bind, that could be causing the problem. Also, watch the chain when the door is being opened/closed with the opener. Is it dragging, hitting something, or jumping around? Next, inspect the sprocket. Is it missing teeth or bent?