I don't know which post to answer. It sounds like your original problem was the door opened too far and the trolley jammed against the bolt in front of the motor unit. Post back and we will go from there.

There doesn't appear to be any way the trolley could jam in a "stuck on to" way but there is evidence on the trolley and the stop bolt of contact wear. When I took the cover off, the trolley did not appear to be jammed, but unfortunately it is not something I thought to look for. Thinking back, this gdo did have a bang and shudder when the opening cycle completed, but it didn't sound like anything to be alarmed about, just thought it was a noisy gdo. After removing the cover and finding the broken nylon gear and the possibility that it was opening too far, ie jamming against the bolt, is it possible that all this jamming cracked the nylon gear which eventually broke, jamming itself against the worm gear and causing the motor hum? As it stands now, I have a motor that runs free but no nylon gear on the opener shaft. Ideally, I would like to replace this gear and adjust the door so it doesn't happen again, if the above seems like a reasonable explanation. If so I would need advice on the following:
1. How do I remove the pins on the shaft to install a new gear? Where do I get a new gear?
2. The troubleshooting part of the owner's manual suggests a broken spring; this is an aluminum section door and I can lift it easily. How do I test the spring? If the spring was broken, would this cause the motor hum or would there be a straining sound instead?
Thanks for the help.