The interrupter cup just presses onto the motor shaft and is held on by friction. I think your motor shaft is moving and causing the cup to fall off. Check the shaft and you will most likely find an e-clip is missing. It also sounds like your door may be out of balance which caused the problem.

Thanks. Can I get an e-clip from a local hardware store and replace it? But, yes, the shaft is moving back and forth. As for balance, that was checked by a tech a few months ago when the door springs broke.

You should find the e-clip at Home Depot.

Thanks for your help. Now, once I get the e-clip (for whatever size the shaft is), where does it go on the mechanism?

Thanks again.

You should see a slot cut into the motor shaft. That is where the clip would go. You may have to dress up the shaft a little bit with a file. Make sure we are right first. It could be the motor bearings are bad.

I don't see a cut. I see part of the shaft sticking out the side opposite the logic board etc. Then the worm gear on the other side, then the area where the interrupter cap would go.

I'd just like to do anything I can myself before buying a new opener. :sigh: Everything seems to be breaking now that I lost my job!

You may have the model that uses a collar and set screw(s). You will need to loosen the set screws and then press the shaft as far forward as it will go and re-tighten the set screws. Make sure you are pressing the collar towards the motor. You will find all this on the same side as the worm gear.

I have no idea. It's a Sears Craftsman 139.53629SRT. I may just live without an opener until I get a job, then replace the whole thing.