I've got the same blinking light although my door does not move at all. I just posted the problem below but posted in the Home repair forum by mistake instead of the Garage forum...is mine a gear issue?
I have a Craftsman 1/2HP 139.18850 (Nov.1995) that has been working flawlessly for 12 years now. Just today it stopped. When pressing the wall button or outside keypad or remote the motor (41A4315-7C) hums once and does nothing. The green light up on the motor blinks 5 times, stops, blinks 5 times and so on.
I've opened it up the motor housing to find a mess of white plastic dust. The door moves easily up and down manually. If the gear was stripped would I not still see it attempt to turn? With the cover off I see no movement at all, just hear the motor hum and that's it. Any help is much appreciated.

I found a site that has some possible solutions to your opener problems. Hope it helps!

Here is a link that might be useful: Garage Door Troubleshooting

Tobe,

Did you replace the gears because they were worn or to try and fix the problem? I would check to make sure that big black cap is pressed all the way on and that the small circuit board with 4 connectors to the left of it is plugged all the way in. Last if you replaced the worm gear as well, make sure you pushed and held the motor shaft all the way back when you tightened up the coupler on the end of the shaft. If all checks out well, most likely a bad rpm sensor. Possibly a bad board, but I would try the sensor first.

Dangardner,

Sounds like the gear is stripped and yes the motor should still operate, but would not lift the door. Make sure the trolley is not jammed up against a stop nut in the front or back depending upon which position it is in. (I.E. up or down.) I haven't seen too many motors lock up after the gear was stripped. Sounds like something else is goin on.

doorguy,

Thanks for your reply. I did have to replace the helical gear only due to the 'shave'. The worm gear looked as good as the new one. I do remember the interupter cup getting knocked off in the repair. I just checked it again and shoved it on tightly. Weird thing is, I was having these inconsistent issues before I had to replace the helical gear. Is it possible the interupter cup was knocked loose as the gear began to fail?

What does the 5 blinks stand for?

It's pretty late, so without waking the wife, I'll wait until tomorrow to check it's progress.

Thanks a ton!
Tobe

Thanks doorguy - I will check to see if the trolley is jammed.

Tobe - Don (the guru) said The LED is blinking the code for "RPM sensor or motor overload". I have the same '5 blinks' on my board.

Tobe,

I suppose it is possible the interuptor cup got knocked loose, never seen it happen but, I am sure it could. However if you pushed it on tightly and are sure everthing else is ok then you still got a problem. As Dangardner said the 5 blinks means there is a problem with the rpm sensor or the motor is overloaded. I would try a rpm sensor and see what happens.

Dangardner and doorguy, thanks for the help.
So far, since I shoved the cap on more and re-adjusted the limit switch assembly (although I don't think it needed it),
things are working so far.

Thanks again,
Tobe