Garage door safety SENSOR problem

lou13September 2, 2008

Craftsman garage door opener 2 yrs. old, door will not go down using the remotes. The door will go down if I hold the button on wall mounted Contol Console. Green sensor light not lite but the Amber is o.k.. Checked for breaks and bad cnnections in wires, all o.k. Bought new Sensors and installed new Green sensor, still does not light up. Now what do I look for? Please help

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I would replace the other sensor just to eliminate that possibility. Sensors must be aligned properly for both lights to be lit. Check the wiring for continuity. It could be broken inside the insulation. Beyond that it is a bad logic board.

    Bookmark   September 2, 2008 at 4:13PM
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Sounds like you may have a short in your low voltage wire leading to the green sensor.

Did you install your own machine? Is your garage pre-wired (behind the sheet rock) or is the low voltage wire surface mounted?

I would check to make sure that a staple used during installation did not puncture the protective coating on the wire leading to the Green sensor light. This would cause a short and result in the problem which you have described.

Let me know if you have any questions.

    Bookmark   September 2, 2008 at 4:14PM
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Hold off on replacing the other sensor until you check the wiring.

You may have not needed a new sensor unit in the first place. If that is the case, perhaps the company you bought the unit from will allow you to return the unit.

    Bookmark   September 2, 2008 at 4:19PM
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Locate your service panel on your machine. This is the area where the force adjustments (2 blue dials with up/down arrows) and "learn button" are. If you don't know where this area is located, it is generally at the back of the motor unit exposed, under the white plastic lens cover, or on the side of the machine (either exposed or under a plastic flap that may read "service center" or "service bay" on it).

Next to the learn button there should be an orange or amber colored L.E.D. indicator light.

Is your light flashing at all? If so, please count how many times it is flashing.

(1) single flash every 10-15 seconds indicates that the infra-reds are totally misaligned or the wire leading to the infra-reds is open

(2) flashes every 10-15 seconds indicates the wire is shorted or the black/white wire is reversed

    Bookmark   September 4, 2008 at 11:57AM
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Thanks Sierra --
I now ran a new test line directly to the sensor terminal on the motor unit, to the new Receiving sensor, [green L.E.D.] while holding by hand, I lined up Green L.E.D.
sensor with Amber L.E.D. -- no luck. The new receiving sensor [green L.E.D.] does not lite. As before, Amber sensor is lit. I think this rules out any break or short in the line. Where do I go from here? Thanks for your suggestions

    Bookmark   September 4, 2008 at 3:41PM
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Hmmmm.......The only thing I can think of is that the black/white wires that connect at the terminal head (motor unit) may be reversed.

Did you check the LED indicator light that is next to the Learn Button????

Just curious, did you purchase Chamberlain brand sensors or some other brand or "universal" product? My experience is that one brand is not compatible with another (Chamberlain/Genie, Wayne Dalton/Linear, Overhead/Chamberlain) and that off-brand "universal" products rarely ever work.

There are several different generations of sensors.

1. Small plug-in jacks (similar to a telephone)
2. Hard-wired
3. Two screws that you loosen, strip one end of each wire, wrap it around the terminals, and tighten the screws down

The generation of sensor should not affect the function of your door, however, how did the low voltage wire connect at the terminal? If you had to strip the end of the wire and push it into the back of the terminal, perhaps you switched the two by mistake when installing the new sensor (an extremely common mistake).

    Bookmark   September 4, 2008 at 7:08PM
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> I was real careful not to reverse the b&w wires on either end.

> The LED light next to the Learn Button works.

> The new sensor is a Chamberlain brand.

> I had to strip the wire and push them into the terminal-- Iwas really careful not to make the mistake of switching wires. I've done that before.

Early on it was suggested that maybe that the Logic Board is bad. Any thoughts about that?

Thanks again for your suggestions. lou13

    Bookmark   September 6, 2008 at 8:13PM
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Ok, you say the LED next to the learn button works, but you didn't say if it was flashing or not.

If it is flashing, please count the number of flashes.

(6) Flashes would indicate that there is a motor circuit failure and Chamberlain would recommend that you replace the RX/LX board.

Before spending that kind of money, attempt to unplug the machine, wait 10 seconds, plug it back in and see if the LED light on the motor head has stops flashing or if the blink count has changed.

A faulty board is not a super-common problem, but it does happen. However, if your machine is only 2 years old, I would be very surprised if both your infra-reds and circuit board failed. If that really is the case, call Chamberlain and discuss the issue with them. They are an extremely good company and the only garage door opener manufacturer backed by the Good Housekeeping Seal.

    Bookmark   September 8, 2008 at 1:43PM
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The LED light next to the learn button does flash. It flashes once [1] and repeats again about every 7-8 seconds.

When I unplug the machine, wait 10 seconds, plug it back in, the LED light flashes 4 times once, and then goes back to one [1] flash about every 7-8 seconds. ?????????????

Thanks, Lou

    Bookmark   September 9, 2008 at 2:21PM
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Random flashing of this LED is normal.

    Bookmark   September 9, 2008 at 3:35PM
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Random flashing does occur. The LED indicator light is not a fool proof system for diagnosing problems, but it does provide some insight as to the issues at hand.

Sounds like you are still having issues with the infra-red sensors

(1) Flash - protector system wire open or totally misaligned
(4) Flashes - Infra-red sensor slightly mis-aligned (dim or flashing LED).

Have you tried Don's original suggestion of replacing the other sensor???

    Bookmark   September 9, 2008 at 5:47PM
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Sorry Don and Sierra, if I followed Don's advise from day one,I would have saved us all grief.

I replaced the other sensor - BINGO it WORKS.

My logic was that that if the other original sensors LED [amber] light was lite, it must be working. WRONG. So much for my logic.

Thanks Sierra for reminding me about Don's original suggestion.

Again thanks to all, Lou

    Bookmark   September 13, 2008 at 12:08AM
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Had the same problem after left garage door open during much rain.
Green sensor random flashing.
Was ready to replace sensors.
On the third day, my sensor "resurrected" and now works fine !
I guess something got wet and took 3 days to dry up inside.
So if your sensors get wet and stop working, allow a few days before you replace them and you may save yourself time and expense.

    Bookmark   April 5, 2011 at 6:00PM
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hey- I am a garage door technician, own my own company here in Ventura County- LA area. If you guy have questions that need answers or need any help let me know.


    Bookmark   April 23, 2011 at 5:12AM
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Garage door will not close when morning sun is shining on the west safety sensor. Must block sun light to get door closer to make the door close.

Is this a typical problem? Are there filters that can be put on the safety lights and not block the two lights from seeing each other?


    Bookmark   May 21, 2011 at 8:48PM
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Either move the sensors back away from the sunlight or use something like the cardboard roll from a roll of toilet tissue to shade the lens.

    Bookmark   May 23, 2011 at 9:52AM
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The garage door wont go up it just makes the sound and goes up a couple of inches also the sensors are green and the other one is red....the red sensor flashes when I put my hand infront while the green remains green and wont flash at all. What could be the problen and what can I do about it?

    Bookmark   August 24, 2011 at 1:38AM
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Remove the cover from the motor unit and check the drive gear. It is a white nylon gear just in front of the motor and it will be obvious if it is bad. The part number is 41A2817 and it comes with instructions.

    Bookmark   August 24, 2011 at 4:07PM
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HI All. Have a Chamberlain garage door opener doing the same thing. Thought it might help if someone would furnish the voltage across the connections at the motor. Across the red & white I get around 24v dc. Across the grey & white I only get .816. That's point 816 dc. Is that right? Thanks, Steve

    Bookmark   September 8, 2011 at 5:15PM
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Why don't you just tell us what your problem is and we will tell you how to fix it. Or come close.

    Bookmark   September 9, 2011 at 4:19PM
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No lights on the sensors. The door opens fine. To get it to close I have to push and hold button till it's all the way down. That's true with the remote or the wall mounted button. If I let up, no matter where, the door reverses and opens. I get one blink on the light next to the learn button. Anything else? Thanks, Steve

    Bookmark   September 9, 2011 at 7:38PM
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Skinned wires at sensors then pulled them out of motor, wrapped them together tested and had continuity where I skinned them at sensors. Put everything back together and still the same thing. That's why I wondered about voltages to see if I had a bad board. Thanks again

    Bookmark   September 9, 2011 at 10:54PM
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The 24volts between the red and white wire is correct. Check for 5vdc between terminals 2 and 3 on the rear of the motor unit. If there is no voltage or if it is greater than 6 vdc the logic board is bad.

    Bookmark   September 10, 2011 at 9:17AM
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Thanks Don. Really appreciate the info. give it a try today.

    Bookmark   September 10, 2011 at 10:10AM
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I was wondering if there was any problems with the remotes, possibly low battery levels or if the sensor was faulty. However if you have gotten new remotes, I am stumped as to where the problem could lie. I doubt I will be of much help.

    Bookmark   December 26, 2011 at 1:19AM
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I had the same people as others on this forum. After rerunning wire and seeing my new replaced sensor still flickering, I came here. Turns out the fix was also the other sensor. Thanks for those that gave the advice!

    Bookmark   December 23, 2012 at 2:11PM
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Hi All,
I just got a new Chamberlain Whisper Belt Drive 3/4 HP garage door opener. Installation was not that hard. But I found that the green LED light safety sensor does not light up at all while the amber LED light safety sensor lit up constantly. I have checked the voltage across the white and grey terminals which reads 5.94 V and I think it is good. I have also checked all the cable straps to make sure no short circuiting.
Following from other forum member, I have also checked the diagnostic LED light around the learn button but found it never lit up.
So am I so bad luck that I just got a busted green LED safety sensor?

Thank you in advance for your time to read my sensor problem and any help is appreciated.

    Bookmark   January 14, 2013 at 5:21PM
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To wonginlok:

Try reversing the connection (the wires) from the sensor to the motor/control board. Each sensor wire has to be connected to the correct wire going to the board. If one doesn't pay attention to that, one has a 50% chance of getting it right. Don't ask how I know!

    Bookmark   January 17, 2013 at 5:28PM
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My Chamberlrage garage door opener that replaced an older 1997 liftmaster seems to operating incorrectly.
When I adjust the the door up and down the units buttons are reversed.. the up makes the door go down and the down button makes the garage door go up. Not really a big deal unit you consider the protection system. It works in reverse as well . Instead of the door going up when it detects an obstruction .. it goes down .. My wife thinks that my installation is wrong .. any help?

    Bookmark   April 20, 2013 at 1:22PM
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Hello all,

I am having the same issue with my garage door. It is a chamberlain liftmaster and upon closing the door, it will retract and the light will start to blink. i noticed the sensor with the orange light is very dim and the other sensor with the green light is out completely. i tried repositioning them, but neither light ever got any better (green stayed out and the orange remained very dim).

My wife did give our garage a good scrubbing with the hose the other day and i read an earlier post that the sensors can get wet and need to be dried and may start working again. Other than that, does anyone have a clue to why the green sensor is completely unlit? How would i check for a short in the wires as they are hidden behind the drywall?

Thank you in advance,


    Bookmark   July 25, 2013 at 1:30PM
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Hi there

We have a Chamberlain ML750. It's been installed for around a year and I just noticed today that the yellow led keeps flashing. The garage door can be opened or closed without any problem. Anything wrong or it is just normal?

    Bookmark   March 25, 2014 at 6:08AM
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