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Sunday, August 20, 2017

Random Garage Door Openings

Posted by admin on December 14, 2011

Last year, my garage doors started opening and closing randomly. At first, I thought one of the neighbors had changed to use the same code, so I changed my code. But, the random openings continued, sometimes I would come home and find the left door open, sometimes it would be the right.

After some research, I came to suspect that the nearby Air Force Academy had switched to using Land Mobile Radio System (LMRS) radios, which operate on the same frequency, 390 MHz, and are known to cause interference. My opener, a Chamberlain 700WHC, has 9 dip switches with + 0 and – positions, allowing 19,683 possible combinations. It seems, though, that the new LMRS transmit 25,000 bits per second, and, sooner or later, the opener senses the right combination of bits and opens. My fix was to retrofit the opener with a new receiver with billions of possible combinations. Unfortunately, the old receiver continued to work; installing the new receiver did not stop the random openings and closings. With online searching revealing that there was no easy way to disable the old receiver, I resorted to good old fashion, tried and true methods, attacking the circuit board with a soldering iron!

Image of Circuit Board

Altered Circuit Board

Conveniently, the circuit board is manufactured with a test point between the radio receiver and the open/close logic. Just above the down force adjustment variable resister, labeled “DNF” (click on the photo to see the large version), you can see where I unsoldered one end of a wire to disconnect the receiver from the remainder of the circuit board. Disconnecting this jumper wire disables the radio receiver. If you don’t want to unsolder it, you can cut it.

Genie Retrofit Kit

New Opener Kit

The new receiver kit uses rolling codes and many more symbols to avoid interference. Installation is simple following the supplied instructions.

Parts Supplied in the Kit

Parts Supplied in the Kit

The new kit comes with a receiver, remote. “wall wart”-style power supply, and wire. You fasten the receiver to the ceiling near the existing opener, connect the wires, plug into power, and train it to the remote.

This change solved my random garage door opening problem. This is a much simpler, less expensive, and less time-consuming solution than replace the whole garage door opener just to get around a radio interference problem!

Comments

8 Responses to “Random Garage Door Openings”
  1. Isaac N. says:

    Brilliant article- we have the same (inherited) garage door opener. We’ve now bought the kit that you have described- excellent solution- thanks!!

    I was going to buy a remote controlled plug/socket but your solution costs much less and makes a lot more sense. ( -:

  2. Isaac N. says:

    Thanks for the acknowledgement/appreciation of my comment.

    My wife and I have attached the wires etc., and it is working; we have a bit of a problem though…

    I assume that I should unscrew/remove the circuit board, in order to get to the ‘business side’ of it? On your photograph it looks like the board is still attached.

    On opening the back of the opener, I am presented with the reverse side of the circuit board.

    I just want to make 100% sure as I obviously don’t want to break it!

    Thank you.

  3. Isaac N says:

    Well, I removed the circuit board, then pried one half of the ‘test point’ off with a knife- it’s working perfectly now(!)… no more having to unplug the opener each night/when we go out somewhere.

    Thanks again x 1,000,000- I am so glad that I found your website!

  4. Isaac N says:

    Wow, I had to ‘double-take’- I can’t believe it was over two years ago! Anyway, it’s still working perfectly- I suppose we’d better buy a new battery for the remote now. ( -:

    (I just saw the ‘bookmark’ that I made for this ‘site, and decide to click on it…)

  5. John Davis says:

    Three remotes: one stays in car, one inside home or pocket when going for a walk. third is attached to outside garage ..ie keypad. If door opens when away in car, then it would not be that remote to be the problem..right ? problem has begun when I installed the external keypad . Help please advise.

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