It’s a Sears Craftsman Garage door opener of unknown age but looks to be well maintained by the previous owner.
1. You can run the door up and down by pulling the red release rope and the door itself works fine with no binding or restrictions.
2. I believe the chain tension is correct. The bottom is just a hair below halfway up the track and seems rather taunt.
3. The “trolley” I believe it is called is located at end away from the motor by the door. Not up by the motor unit when the door is down as it should be and I can force it to move an inch, I do not believe it to be stuck.
4. When you activate the motor from the wall switch it runs but the chain does not move. Even with the door released (effectively a weight off situation).
5. I have reached in and can move the gear on top of the unit maybe a quarter if an inch so I do not believe the gear on top of the unit to be stuck.
6. I can “help” the door up and down by lifting/pulling it. But it is jumpy however it stops at the right times on both ends.
7. Both green lights are illuminated on the safety sensors (this would not stop it from opening anyway… would it?)
8. last but not least the green flashing light on the unit. It is erratic, it flashes once then five seconds later once but sometimes twice and then 10 or more seconds it goes back to one flash then maybe one flash then a few seconds later two. The only constant with this is I have never seen it flash twice… well twice in a row.