I have a Sears garage door opener. When activated, the light comes on and the unit hums for about 3 seconds. The light goes out in about 3 minutes. The door will not operate. I don't think this is a problem with the motor being out of pahse or a problem with the springs or door or trolley. This same thing happened about a month ago and I also noticed smoke coming from the unit. After about an hour, all was working fine again until now. I also just noticed that the small light on the back of the unit is blinking... 5 blinks, pause, 5 blinks, pause, 5 blinks, and so on. Any suggestions would be GREATLY APPRECIATED!! I'm thinking I need to replace the capacitor but don't see how the blinking light on the back of the unit is related.
Thanks,
Danf

Sounds like the motor is shot. The blinking light is problaby some type of error code or something. Look in the manual or go online with the model number and checkit out. OR call Sears and ask.