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  1. #1
    RJT
    RJT is offline Stainless
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    Can someone explain to me how a garage door opener knows when it is at the top of it's stroke? About once a month mine overtravels into the hard stop. I have to loosen up the chain, push it off the stop and then it works agian for about a month. Is there some kind of transducer on the sprocket, or sensor on the position of the door (like the beam at about 6 inches off the floor to make sure nothing is in the way when coming down)? I can't see how it works. Its a liftmaster 1/3 hp professional series, about 2 years old. The manual is long gone. Thanks, RJT

  2. #2
    JoelS is offline Cast Iron
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  3. #3
    RJT
    RJT is offline Stainless
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    The manual only tells how to adjust it if the travel or force is not correct. Mine seems to be correct when it is working. It just overtravels and hits the stop randomly. Usually it stops about 2 inches from the hard stop.

  4. #4
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    Should be a limit switch that contacts the moving carriage. (The carriage here is the moving sled that is tied to that J-shaped bar and ultimately the door itself)

    Likely it is not making the contact reliably...solutions range from tearing down the switch and fixing it, buying a new OEM part, or getting something industrial like Al Bradley or Square D and adapting that to the application

  5. #5
    RJT
    RJT is offline Stainless
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    There is nothing that the carrige contacts (except the hard stop for overtravel which is nothing more than the head of a bolt) The chain goes around a sprocket but there is nothing on the chain to contact anything inside the cover. Got me stumped.

  6. #6
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    Ok, other possibilities...1 or 2 special links in the chain, a prox switch...???

    What does the manual tell you to do as far as adjusting it? I can't see the manual without the model #.

  7. #7
    J Henricksen is offline Stainless
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    some openers have a threaded shaft inside the motor control box with two switch dogs that move as the operator turns. These are what trip the limit switches. usually there is a spring rail that keeps the dogs from turning. You can push the rail away from the dogs and turn them to set them for proper up and down stopping.
    Maybe you have that type of limit switch setup.

  8. #8
    gmatov is online now Diamond
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    RJT,
    What KIND of opener do you have?

    Nobody can tell you how to stop the thing up OR down if they don't know what KIND it is.

    Cheers,

    George

  9. #9
    winchman is offline Stainless
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    I've got one exactly like that -- A Liftmaster 1/3 Professional with a chain drive, but it's 14 years old. Mine has adjusting screws (one for up travel and one for down travel, IIRC) on the other end of the case, away from the door. I had to adjust it when I replaced the seal on the bottom of the door two years ago, but it's been rock solid since.

    I think there's a threaded rod attached to the drive system with a traveling nut that runs into limit switches at either end. My guess is that your up-travel limit switch is going bad.

    Roger

  10. #10
    Kevin Singleton is offline Aluminum
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    Winchman is exactly right. The Chamberlains (and Sears) chain-drive door openers have a set of limit switches inside, and a driven screw that moves a contactor back and forth. It's possible that the "up" limit is sprung, or wobbly, and needs to be reseated. They're not very well-made, any more. I spent 10 years of my early working life installing about 10,000 garage door openers just like this, and this issue was the most likely service call I'd receive on any particular day. Unplug the power, and crack the case. You'll have it figured out in no time.

  11. #11
    winchman is offline Stainless
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    Well, rats.

    I just got up close and looked at the adjustments, and they say "Up Force" and "Down Force" with "hi" "medium", and "low" range markings on each. That would suggest they are measuring torque, probably indirectly by measuring motor current. The adjusting screws appear to be potentiometers mounted on the printed circuit board. I'm afraid that makes fixing the problem a little more involved.

    I obviously saw the traveling nut arrangement on one of the several other openers I've installed or worked on. I apologize for the mis-information with regards to the Liftmaster.

    Roger

  12. #12
    John Michael is offline Senior Member
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    The up force aqnd down force adjustments are not the travel limit stops, they are what stop the door if you close it on the hood of your car or if your springs get weak and the door is too heavy. They force pots should be set at the lowest setting that will let the door operate reliably. There are limit switches somewhere to stop the door at the ends of its normal travel. I recently installed a Genie and was surprised to find the stop limit switches were normally open, they have to close a contact to stop the door. This is not really fail-safe, they should be normally closed and open to stop the door like the limit switches on a CNC machine tool axis. If your limit switches are like this you may have a dirty or burnt contact on the limit switch. It is exagerating to call the ones on the Genie "limit switches", they are little more than a couple pieces of shaped copper being pushed together.
    I think Genie and Liftmaster are both owned by Overhead Door Co..

  13. #13
    winchman is offline Stainless
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    John's correct. There's also a pair of adjustments on the side for travel. I had to move some stuff to see that side. I got curious, so I opened it up.

    In this photo you can see one of the nylon adjustment screws (middle right) and the traveling nut assembly (in the mirror placed in front of the motor. Yeah, those really are pretty chintzy limit switches.


    My Liftmaster was made by Chamberlain.

    Roger

  14. #14
    Joe McDuff is offline Senior Member
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    Limit switch(s) are going south. Probably a MicroSwitch by brand and of sufficient quality to match the rest of the mechanics. Installed a Sears chaindrive, and after 30 years of use the only problem was with the funky trolly which rides the rail. Rebuilt it with a torch and a little reinforcing, still going strong.

    Now, to rob this thread, today's problem is a Genie screwdrive, which worked great for about 10 years. There is a cktbd with three miniature relays--timed garage light--UP circuit--and, DN circuit. It smoked. Genie says, no longer available. Great, just buy a new machine for 175, and throw this one in the trash.

    My Scottish blood has me searching for a source of repop cktbds, where I can purchase a new/recon board and get back in business. Even if someone has available a wiring schematic, showing the connections to a later version of the board, I can rewire the electrics. I would even buy/install the 2 IR sensors, if required.

    Suggestions, source of manuals, schematics????? I'll dance at your wedding.

    J

  15. #15
    gmatov is online now Diamond
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    That's the problem with this electronic stuff. Works on smoke. If you get a leak, and the smoke escapes, won't work any longer.

    Friend had the same problem, with a Sear's opener, likely Chamberlain, that year. Went to the Service Center near here to order new one. Something like a hundred bucks. NO WAY!!

    Looked at the returns set out for sale, refurbs, bought a whole assembly, power head, rail, chains, transmitters, etc., for about 75 bucks.

    He was a Millwright, not electrical, so don't know if he would have been ABLE to replace the circuit board. Decent mechanic, though, he could replace the power head. He's happy and ahead of the game.

    Cheers,

    George

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