Were do I start troubleshooting my 1/3 horsepower Craftsman/Sears Automatic Garage Door Opener Model Number 139-185706. Push button AGDO buttons don't work; the outside motor light does not work; and there is live power to the rafter mounted unit. Could the motor be shot already? Where do I start to try and find the problem? There is NO manual or schematics either. Thanks, Mark