You have an unusual problem. It sounds as if the motor is struggling to open the door and the built in thermal protector is opening. This automatically resets when the motor cools. Try disengaging the opener from the door and opening the door manually. You could have a broken spring above the door and the poor old opener can't handle it.

Thanks for the idea. I'll try doing what you said tonight. By the way, what is thermal protector and where it is located?

On a side note, what does "capacitor" do? Capacitor is one of the common replacement parts (in addition to logic board and rpm sensor) listed for LiftMaster/Chamberlain models.

The thermal protector is inside the motor and is not something you can replace. The capacitors only function is to give the motor a little extra kick to get it started. Once started the capacitor is along for the ride.

Ok. I disengaged the opener from the door and tried opening the garage door manually. It went very smoothly. Almost no effort required. I also checked the springs above the door and they appear to be in good shape.

I then tried to operate the motor with the door disengaged. It moved a little bit farther than when the door was engaged, but still stopped very quickly and went into a "sleep" mode. Maybe it moved 15-20 inches as opposed to 4-6 inches when the goor was coonected. Does it sound like thermal protector problem? Without the engaged door the motor should not have any restrictions on going back and forth, right? Weird...

There is nothing I can think of other than the motor itself that would cause the problem you describe.

was the problem.ever solved was.it the logicboard rpm cirquit or the motor ?