I had a problem with my garage door opener. I would push the button and I would hear it spin, but nothing would happen. I unplugged it and took off the cover and much to my dismay I saw a bunch of shredded plastic gear.
So I'm documenting the problems I ran into and the solutions I used so others may benefit (which is not my blogs purpose at all, but since I didn't find some of this information on the web, I figured I should document it).
Ok, I found it was much easier to work with everything by taking off the entire bottom portion of the garage door opener. This was the part I needed to order: http://www.amazon.com/Chamberlain-LiftMaster-Craftsman-41C4220A-Sprocket/dp/B00023RTD6 I actually thought I only needed just the plastic gear and attempted to remove it before I found out you had to have a special tool to remove the pins to slide off the gear. And I'm glad I did end up buying this kit, because on closer inspection the worm gear also needed to be replaced. I ended up using all of the parts, minus two parts that were for slightly different openers. There's plenty of sites that discuss that replacement process already. http://dl.dropbox.com/u/1347192/lifter/liftmaster_repair.html was the one I found. I didn't want to take the opener that far apart, and ultimately did not but got pretty close. It ends up being easier than you think, so just do it. I left the motor in place, as well as the front side where the light is. But the other parts come off easy, so just remove them and two screws on the bottom front to completely detach it.
I would probably have avoided a lot of pain by following those instructions on the other websites closely. But after wedging off the bushing, replacing the worm gear, tapping on the new bushing, putting everything back together I followed the last part of the instructions in the manual you get with the kit that said to have the door closed. Well, that was a big mistake.
Its better to remove the pin from the trolley and have it completely separated from the garage door. And another thing is that you should check and install the safety bolts in the rail if they aren't there already. My home builder apparently decided those weren't critical. So while I was playing around with it trying to get it working, I nearly broke the T rail. I was very fortunate there wasn't a big accident, but I ended up having to remount the T rail as it literally stripped the bolts out of the board it was mounted to. Fortunately, my home builder ALSO didn't put all the bolts in when bolting it to the wall, so I had a few other holes I could use to remount the T rail.
Anyway, onto the other problem I ran into. I would click to open the garage door, it would send the trolley down about 5 inches, bring it back up 5 inches, and stop for no apparently reason. There was a little green led light in the back of the unit that flashed 5 times. Doing searches, I found other people who had run into this and no solutions. Suggestions were that the RPM unit needed replacing. I found that hard to believe, and on the FixYa site it was even mentioned by one of the people that after replacing it twice it still didn't work. The manual I found online also indicated that it could be a faulty RPM sensor or a bad logic board.
Well, the problem was actually caused by the way I had reassembled the parts on the main motor shaft. When you slide on the bushing and all of the other pieces, push them down tight. It shouldn't move back and forth much more than maybe 1/16". The little black cap on the end passes through the RPM sensor. http://www.amazon.com/Liftmaster-41C4398A-RPM-Sensor-Assembly/dp/B000JGLXDI take a close look at it. On the circuit part that it passes through there is a little eye and corresponding light on the opposite side. If the cap isn't on far enough, the sensor will not see the cap and therefore will not think that there is any rotation happening at all. That's what was causing it for me.
Also, take a close look at the bottom where there's three plastic screws (limiter adjustments). The middle one slides back and forth as the motor moves the trolley. When the metal contact on the left or right side of it makes contact with the metal contact on one of the two other plastic screws, then it will stop moving. I had moved these out of the way of the middle part that slides to make sure that they weren't causing the problem. When they are in the way, it will actually stop the unit from going further in that direction -- they do not cause it to reverse.
What I did was moved the slider in the middle screw to the middle of it. I adjusted the other two so that it didn't have far that it could travel before coming into contact with them. Then I carefully plugged in the unit and avoided touching any of the electronics and capacitors and watched what happened as I ran the garage door opener. I saw the way the limiter worked and that made it much easier to understand how I needed to adjust it.
Anyway, if you're reading this, you probably have run into the same situation, so good luck.
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