Help - Erratically functioning Liftmaster
Here's one you don't get everyday, I hope you can help me out. My Liftmaster started functioning erractically today. It will open various distances and just stop at various heights. This all started when I walked under it while it was opening and nailed my head on the bottom of the door - hard enough to make the door stop (yes - this hurt quite a bit). If I disconnect the door, the trolley seems to go back and forth just just fine - the problem occurs only when the door is attached.
Can jarring the door upwards, while it is opening, damage something specific in the opener? Any help on what to focus on first would really be appreciated.