Well, rather than a repair, I just moved into our house (3 years old) and the third car opener has never worked right. It initially would go up, but not down, and didn't stop at the top, it just jammed and vibrated against the opener unit. I opened it up to find that somehow the open adjustment stop was bent and the locator just went right by it and kept trying to go up. I righted that situation by bending the stop back and setting the open travel adjustment properly. So now, it will open, and when hitting the stop, does stop. But, it will not close. I can manually close it by removing the belt from the motor and getting everything set at the bottom, then push the button and it opens again and stops properly at the top. Holding down the button does no good, and I can confirm the photo sensors are aligned properly because if I block them, the opener lights come on. It just seems to me that whatever switch exists to tell the opener it is at the top and needs to reverse direction has failed, but I have no idea what that is or how to fix it. I did find the start capacitor you guys were talking about (big blue guy, 4 wires, two red, two blue). My terminals are top and bottom, with connections on each side of it. The reds are on the bottom, and the blues on top. My opener is model 139.53954. Thanks for helping.

Could it be any type of radio interferance, like from my wireless router? How can I tell my transmitters are working correctly? Otherwise I guess my best bet is to buy a new opener since a new logic board with shipping is near the price of a new GDO. Thanks for your reply.

Ok, double check your work around the RPM sensor. You may have the motor shaft slid to far forward not allowing the Interuptor cup to fit properly on the shaft. There has got to be something throwing off the Rpm sensor. I can't imagine it would just go bad all of the sudden it is possible I just don't think it is probable. You might try loosening the coupler on the back of the motor shaft and make sure you have all the bushings in the correct spots. You should have a flat washer, a washer that looks bent and a ring that slides over both of those and then the collar. If it is all in place push on the front of the motor shaft opposite the side of the collar. Push it back as far as it will go and hold it there while you tighten the collar back up. Put the interuptor cup back on leave the cover off and watch everthing while you hit your transmitter, see if anything looks out of whack, if not, I would have to say you have a bad Rpm Sensor.

Make sure the black cap is on the back of the motor shaft and pressed all the way on. Make sure the 4 pin circuit board next to that black cap is plugged in. If neither one of those two are the issue and you replaced the worm gear as well, what you will need to do is loosen the coupler up on the back of the motor shaft. On the front of the motor (door side) where that shaft pokes through, push it back as far as it will go and hold it there while you tighten the coupler back up. One of these three problems is always the issue for people who have done this repair themselves.