Hello to the forum. Hopefully someone can help me with this problem. Craftsman model 139.53635SRT1. The unit is probably 8-9 years old. For the most part, it's been a good unit. It ignores the up-limit switch once or twice a year and jams against the safety bolt, but that is easily correctable....and I've replaced the plastic drive gears once....but otherwise it just worked like it should over the years. All of a sudden however, it doesn't want to open or close reliably.

Symptom #1: Sometimes when I try to close the door from the fully up position, it moves the door down maybe a foot or so, and then reverses it back up a small amount and stops. It acts is if it is sensing something in the down path and reacting accordingly.....but the light on the front of the main control unit does NOT flash when this problem occurs. If I hit the wall button and stop the door just as it wants to start back up, I can get the door to stay in place. When I push the wall button again, the door will again start down, but only travel a foot or so, and then go back up a short way and stop. If I repeat the above process over and over, I can make the door close completly a little bit at a time. When trying to close the door, if I push and HOLD the wall switch, the door will fully close as it should. (Makes me think a sensor problem....but why doesn't the light on the front of the control unit flash off and on)? (Also see later on for more info on the sensors).

Symptom #2: Sometimes when I try to open the door, the door will move up only a small amount and then reverse a small amount and stop....kind of like Symptom #1, but in reverse.

Now for some additional information. First of all, sometimes the opener works correctly, opening and closing the door as it should. Sometimes I can make the problems go away by unplugging and plugging it the control unit....but sometimes not. Sometimes the problems just go away on their own. When the problems do occur, it is not a physical problem with the door itself. The symptoms occur even with the door disconnected and the trolly moving freely on the rail. At no time does the main light on the control unit flash on and off. Both the emitter and receiver LED's in the safety sensors are a steady bright green. I have realigned the sensors with no effect on the problem. I have also verified all wiring between the sensors and control unit with an ohmmeter plus I stripped and reattached the wires at the control unit with no effect on the problem. I have disconnected and reconnected the connectors to the limit switch assy and the logic board with no effect on the problem. One final note, the indicator LED on the logic board usually blinks five times over and over when the problems occur.

I'm thinking the logic board is probably going bad....but maybe someone else can offer some advise? Please?? How about it Don or GDS if you're out there? You guys certainly seem to know what you're talking about. Any help from anyone will be greatly appreciated! Thanks in advance!