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My garage door opener (LiftMaster 1/3 HP) stops partially through the cycle of closing the door.

I have removed the chain from the gear attached to the sprocket, and tried cycling it like that. I wanted to see how it performed with no weight to lift.

The problem persists. Even with no chain attached, the thing stops before it gets to the "bottom" position.

Also, I noticed that the stopped position of the sprocket is not all the way to the electrical contact for the "top" of the door.

So in other words, something is jamming the sprocket to only be able to move a couple feet between the full-up and full-down positions.

I just finished replacing the sprocket assembly, and this problem still persists.

What else could be causing this problem? The motor? The worm gear? (Worm gear looks fine upon visual inspection). Or is it just time to get a new opener? I believe the current opener is about 15 years old.

  • How long does it run before it stops? Will it happily run up and down, stopping when it hits its mysterious limit(s)? – Daniel Griscom Aug 22 '15 at 22:24
  • Not long. Probably like 2 feet with the chain on. But yes, it runs fine when it is moving. – dan-O Aug 22 '15 at 22:27
  • Once it's stopped, will pressing the button run it the other way and then stop, and then back again if you press yet again? – Daniel Griscom Aug 22 '15 at 22:45
  • No, it goes down and then stops and then goes back to its original position all in one click. – dan-O Aug 22 '15 at 23:09
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Garage doors have two pairs of settings:

  1. End stops: one at the bottom and one at the top
  2. Force limits: one for heading down, one for heading up

The first pair is obvious: you want the door to stop right when it's properly closed, and right when it's fully up; you don't want the door to stop too early. You've looked at these, and they seem to be fine.

The second pair is less so. If something blocks the door, you want the door to stop moving, rather than squish whatever is in the way. In fact, the doors I've seen, if they hit the force limit on the way down, will immediately turn around and open (so if, e.g., it closed on someone's leg, it wouldn't keep them pinned). There are force settings for both going down and going up, and must be adjusted with the door and lift springs attached.

See page 24 of this Liftmaster 1/3 HP manual (you may have an older model, but the idea's the same). My guess is that your downward force setting is too low, so that the opener thinks something is in the way and reverses.

You may also have a model with a sensor beam across the bottom of the door, to stop the door closing if there's anything in the way BEFORE it hits the object. If that sensor isn't working you might get the same symptoms.

  • Yes, I tried cranking the force limits all the way up (to 9kg is max), and I saw the same result. (It isn't the sensor beam, because on my model it flashes the opener light 3 times when it sees something in the way.) I'm thinking my unit is screwed, because if it can't get past whatever is stopping it when the chain is disengaged and at full force, then it is toast. Thanks a lot for your help with this. – dan-O Aug 22 '15 at 23:55
  • Be aware that the measured force may depend on that chain. You might try reassembling things with the force set to the max. Then, try again with the force set to min. – Daniel Griscom Aug 23 '15 at 2:41
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I would bet on a bad main board - Garage door openers have been little computers for some time now, and they don't live forever, especially if nailed by lightning/power surge.

How much I would bet on the board is, however, debatable - where I had a 2 year old opener with a pretty clear strike nearby that was acting up, I opted for a new main board - but it was half the cost of a new opener, and it came with no warranty. I rolled the dice on that and got it right, but I could have just as easily had a part that didn't fix my problem.

For a 15 year old opener, I'd choose replacement, since a new opener is not very expensive and will typically have a 90 day or 1-year warranty. It's easy to spend more on (often non-returnable) replacement parts than a whole new opener.

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