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I have a Craftsman 1/2 HP garage door opener. It's always been a little finicky, but tonight it stopped working. In the middle of going up as tonight, the door halted, leaving a gap between the door and the ground. I got out of the car, squeezed under the door and realized the motor was still running. My wife pushed the door opener a few more times, but the door wouldn't move despite the motor responding. I pulled the release on the door and opened it all the way. I realized parking the car in the garage would be a hassle, since I would have the open the door manually again. So I just closed the garage with the chain disengaged.

The motor will start and stop in response to button pushes like it is supposed to - normally the first push starts it in one direction, the 2nd reverses the direction and the 3rd will stop the motor. However, the chain has completely stopped moving (and by extension, so has the door). This causes the motor to run for an extensive period of time before it seems to timeout and give up. The chain and door connector assembly haven't budged since.

I've not worked on garage doors before, but I have a degree in Computer/Electrical Engineering. I've never studied to be an electrician or anything, so I'm well aware there are a lot of things I don't know about this. But generally speaking, is this the type of thing I could potentially fix myself? Or is it more likely the whole unit is shot and I should just call a repairman up front?

I know I have the manual around here somewhere, I'll keep looking for it and list exact part numbers if I find it.

Update: I popped the sprocket protector off just like in the video form Steven's answer and the chain is still firmly attached. When the motor is running, you can clearly see the shaft and sprocket are not moving at all, not even jerking when starting or stopping, like something had locked up the shaft.

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Have you checked to see if the door can be moved manually? Pull the release handle and ensure the door can be lifted –  Steven Jan 20 at 0:54
    
Ah, yes it can move manually. Added details to the question. –  Patrick M Jan 20 at 3:42

2 Answers 2

It sounds like the chain might not be on the sprocket that drives it. Get up on a ladder and look at the top of the unit. You should be able to easily see if the chain is off the sprocket. Try running the opener while you are up there too.

If the chain has come off you will need to loosen the chain tension, place the chain back over the sprocket and tighten it to the correct tension. Your user manual should have details on how to perform this but usually there is a screw you adjust on the trolley that controls the tension. Make sure to disconnect your door from the trolley before you do this.

Here's YouTube video that shows the process.

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That sounds straight forward enough. I was jumping up (I'm quite tall) and didn't see any moving parts on the unit at all - I'll probably have to open the case. That video looks spot on, symptomatically, but I think the sprocket has a separate housing covering it on my unit. I'll give it a shot this weekend. Edit: Just got to the end on the video and I see the cover. +1 to you sir, I'm confident this will fix my problem :) –  Patrick M Jan 17 at 3:50
up vote 0 down vote accepted

I ended up having to have this replaced. I got a repairman out on a 'free housecall' who quoted me a price for the parts & labor. The price was less than a replacement, but the fellow warned me no one would warranty a repair on a 15 year old unit beyond 30 or 60 days. The unit originally had a 10 year warranty and was installed in 1999 (Craftsman garage door opener warranty page, for reference).

It's possible that the fellow really needed to sell a unit and was underselling the feasibility of the repair. But I'll never know because I sprang for a replacement unit with a lifetime warranty through both the installation company and the manufacturer.

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