jiyu - If it is the remote you can buy a replacement and it is easily programmable. My mother has a Craftsman 1/2 HP unit like this, which is actually made for them by Liftmaster, and if memory serves there should be a button where the wires connect to the unit that states program. Press that button at the same time you press the button on the new remote until it starts flashing and the remote should be programmed. This may not be exact, but there should be instructions with the new remote and if not have Sears pull out a manual on one of their openers. Also my mother has a switch on the wall that looks like the remote and one of those 3 buttons has a lock symbol, that locks out the remote, so that no one from the outside can access the unit with a remote. She accidentally pressed that button by mistake and her unit stopped working, so you may want to check that on the wall and remote. The light problem you mentioned could be a sign of a more serious problem. Good Luck!

I figured it out. Problem with adjusting the limit switches was due to a missing pin on a gear that is on the main motor shaft that turns another gear that moves a plastic screw that hits the up and down limit switches. In other words, the internal up/down limit switches were not getting consistant feedback of the garage door position. Nothing that a twisty tie from a garbage bag couldn't fix. So that problem was fixed. The garage door now moves and it now moves up and down without whacking the header going down and the stop limit bolt (protecting the GDO motor unit) on the way up. I knew I was wasting time when the manual says a single rotation on either screw would result in a 2 inch travel change. and nothing I did was consistant. It either hit the bolt or header or it would just HUM and not do anything. I think the original problem of why the belt's tention spring/bolt came undone was due to excessive vibration due to non-sufficient belt tension. As soon as i got the garage door operational, I noticed it was hecka jerky initially going up or initially going down. Mid-travel was smoother. By tightening the nut (collapsing the tension spring) to the 1.25 inches specified in the owners manual seemed to make the garage door much smoother. When I have the time, I'll adjust the force screws down. I think I have them maxxed out right now. I'll also test the safety/reversing feature. For now, it open and closes smoothly. I'm happy. So, while the owners manual didn't tell me to open the thing up, common sense told me to. Also, this unit has a diagnostic feature. When you press the LEARN button, it will light up the diagnostic light and blink. 5 blinks told me the motor was overheated or the RPM sensor wasn't happy. No mention of what the RPM sensor was. I'm assuming something was stuck. Anyways, adjusting the limit switches got it moving and once I cracked open the motor housing case and saw the limit switches in action and saw how misaligned they were, it was a pretty easy fix. Glad I disconnected the door so I could cycle the belt for testing without crashing the door. that made way too much noise at 10PM tonight. Once again, thanks for your help and I hope something in this helps someone.

Don, Thank you for your patience. I finally had some time last night to take the garage-door opener apart a bit and test the voltage with my multi-meter. I had some difficulty figuring out which terminals were 2 and 3. I tested several wires and combinations between the white, blue, and red wires that came off the back of the motor. My voltage readings were no higher than 1.5vdc. Again, I may not have had the wire combinations correct, though I tried many different combinations. Also, the garage-door opener was working perfectly: could not get it to act up�. Here�s what I discovered� There is one white, red, and blue wire that come off the back of the motor. The white wire goes directly to a connection point (for power, as it is the power line that comes into the unit and branches off to the motor and etc.) and branches off to the logic board, lighting and other components such as the up/down force and up/down travel�. The blue and red wires come off the motor and hook to a cylindrical component (about 4in. in length and 1in. in diameter) and come out of the same cylindrical component at different connection points and those connect to the what I believe is the logic board.. In other words, there�s a red and blue "in" connection point as well as a red and blue "out" connection point� I�m not certain as to exactly where I need to test for voltage�. Can�t get the opener to act up now that the weather is warmer� Thanks for your help and additional advise� Fred

The problem I have is my door wont open at all. Neither the remote nor the wall button will budge it. The wall unit and the overhead opener seem to be communicating, since the lightbulbs are flashing, and turn on and off when told to. The remotes seem to have no affect at all. I replaced the chain onto the sprocket assemby and was adjusting the up and down on the main unit, Unit does nothing now when I press button on wall, is it possible to have adjusted the up/down too much to make unit not operate?Anyone have any ideas why my door won't work at all? I would expect the motor to at least chug or something, but...nuthin! Just flashing lights when i press the wall buttons. Sears Model 139.53975SRT1. HELP!