Old doorman model r won't move closing direction

have an old automatic doorman opener model R that was working but after a little lube on chain/pulleys etc, it started snapping immediately back and forth changing directions. now it will only stay at upper limit or return to up position if manually cranked forward, will only go in up direction. relay(?) clicks every time i hit remote, but will only move one way. why?.. what makes the motor REVERSE when i push remote and did i t short or burn out cuase it will not go down direction at all.. i have no eye sensors on this cheap old unit.