In some cases dirt on the lens, a small imbalance, or a loose sensor brace may create the sensor to believe something may have damaged the sensing unit light beam. Sensing unit Electrical wiring If that may not resolve the issue, it could be the wiring in between the sensors http://sethatpkt.blogginaway.com/5448483/some-known-factual-statements-about-garage-door-off-track-repair-reseda