Symptom: Everything Works Fine Except the Lights
Fix: Replace the light socket
If the bulbs are OK but don't light up, you probably have a bad light socket. To replace the socket, you'll need to remove the circuit board to get at it. Use the same steps as in 'Replace the Circuit Board' (above) to accomplish this.
Once the circuit board is removed, pop out the old socket by depressing the clip that holds it in place. Remove the two wire connections and install the new socket. Replacement sockets cost less than $15.
Be sure to use a bulb of the correct wattage. Using lightbulbs with a higher wattage than the socket is rated for will cause a socket to fail. Not only is this bad for the socket, but it can also be a fire hazard. If your light cover has turned yellow from heat, you're probably using too strong a bulb.
Symptom: The Trolley Carriage Moves But the Door Doesn't Open
Fix: Replace the trolley carriage
If the trolley carriage moves but the door doesn't open, the culprit is probably a broken trolley carriage. Before you pull the old one off, clamp down the chain to the rail. This will help maintain the location of the chain on the sprocket and speed up reassembly.
Once the chain is secure, separate it from both sides of the trolley. Disconnect the rail from the header bracket and move the rail off to one side. Slide off the old trolley, and slide on the new one. Reattach the chain and adjust the chain tension. Replacing the trolley on a belt drive and replacing it on a screw drive are similar procedures. A new trolley will cost $25 to $40 depending on your model.
Symptom: The Opener Makes a Grinding Noise But the Door Doesn't Move
Fix: Replace the main gear drive
If the garage door opener makes a grinding noise but the door doesn't move, your main drive gear is probably toast. The main drive gear is the plastic gear that comes in direct contact with the worm drive gear on the motor. The main drive gear is the most common component to fail on most openers.
Replacing it is a bit more complicated than the other repairs in this article but still well within the wheelhouse of the average DIYer. There are several components that need to be removed before getting at the gear. Get a detailed description of how to rebuild a garage door opener.
Once you get the gear out, you can remove it from the shaft with a punch, or you can buy a kit that comes with a new shaft. Make sure you lube it all up when you're done. The gear alone should cost you less than $20. A complete kit that comes with the shaft will cost closer to $40.