Garages and Carports - Chamberlain door opener failure

I have read the various threads in this forum regarding Chamberlain garage door openers, but have not yet figured out what's going on with my Chamberlain Model 1200 that I believe was installed in 1998.

The opener does not close the door. Pushing the remote or the wall switch turns on the light and clicks a relay, but nothing else. Holding the button down does not change this.
The green light flashes five times.

I looked at the RPM sensor and everything appears to be clean. The sensors appear to be lined up correctly, with strong green lights on both units.

I backed off the upper limit contact screw and pushing the button made the motor run and move the trolley another inch or two until it lodged against the vertical bolt. Backing off the contact screw further and pushing the button clicks the relay and makes the motor hum for a few seconds.

I did find half a broken washer (1/2" ID) sitting in the cover. Not sure where this came from, and I cannot find the other half anywhere.

I'm not sure what to do next. Any suggestions?

Thanks in advance,

Strabo

Wish I had seen your post earlier. Remove the bolt the trolley is running into and then run the opener until the door closes. While the door is closed turn the 'up limit' control on the side of the motor about 5 turns in the opposite direction of the arrow printed on the cover. Remember to replace that bolt.