The master link connecting the cable to the chain on my Sears Craftsman 1/2 HP G.D. Opener (Model139.53627SRT, 6/93, Ser 25235A01358) broke while attempting to open the door.
I replaced the master link with the door in the closed position. Pushed the wall control push bar. The chain moved to further close the door, exerted pressure on the header bracket and brace and then reversed itself. The chain moved to the original closed door position (with the trolley about a foot from the end). On second try broke the master link attaching the cable to the trolley. Replaced that master link.
Unit still moved in direction to further close the door then reversed and stopped as before.
I pulled the emergency release to disengage the trolley, hoping to hook up the trolley with the door in the "open" position. With the trolley disengaged the chain still moved to close the door and still reversed to stop at the same position as before (inner trolley about one foot from the door end of the T-Rail).