Sears Garage Door Opener 139.53990D opens a bit then shuts

[Vatic]

Okay so I have a 3-4 yr old sear 3/4 horse power garage door opener (GDO). I recently went to open the GDO but it only close furtherer, now this unit has been working for yrs. Tried it again and the same thing tried to close further and at thsi point has jam the door into the ground. After severl hefty hanks on the door release was able to get the door free and was able to open it, but did not want to due to the chain hanging down low enough to get grease on the freshly painted door.
Since I still had all this pressure on the chain I loosen'ed the chain and popped it off the gear, be careful not to get anything caught in it. Then with the chain off the gear I attempted to open the door but it only closed about two feet then opened right back up that two feet, I did nothing to make it return, the sensors were not blocked no blinking light just came right back to the initial starting point.
I check the up/down pressures and adjusting these had no effect on the motion. I then was thinking maybe the plastic gears had a issue so I diassembled the unit and they were all fine. checked all electrical connections and noted nothing. Check the limit switches and one was being made while the other wasn't as excepted, since the door can't be both open and closed. Tried the door again and got the same thing it would move away from teh sensor about one inch on the sensors but then reverse direct adn come back to the starting point.
I continued to mess with it and got it to open and close correctly and set up the open and closed sensors and the open and closed force, reassembled the unit and it opened once correctly and then back to the opening only a bit then closing, note this is reverse from what it started as. Anyway so with this acting up any ideas? The logic Board?

Thanks for any and all assistance,
Vatic

[norlando]

Sounds like you have done a thorough troubleshooting process.
RPM sensor becomes a suspect after you have eliminated everything else.

[stampdoorparts]

Check travel limits, rpm sensor and make sure your springs are not broken on top... worst case check the circuit board/replace. Also check for a short in wiring.



Stamps Garage Door Parts
Stamps Garage Doors - Illinois

[TJR]

You said the gear was fine. Did you see any black stuff on the white gear inside the box? If so you need a gear/sprocket rebuild. The bushing @ the sprocket is bad and the shaft is pulled forward so the small gear @ the bottom for limit switch will skip. Readjust your up and down force and do your safety reverse test. Make sure your door are balance corrrect.

[DoorPartsWarehouse]

Sounds like a logic board issue. Might want to get it tested.