Question about liftmaster Chamberlain Garage Door Opener Transmitter 300MC

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Garage door light beam one green the other yellow - light on yellow does not go out even when you block the beam

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For Genie openers, normal operation is: when you block the beam, green light on one side stays on, while the red light on the other side flashes. The side with the green light is just a "dumb" infrared (invisible) light source; it doesn't know or care what happens to the beam. The other side is the receiver (photocell), and has all the smarts, so knows when the beam is broken, flashes (or turns off) its light, and sends appropriate signal to the opener to prevent or reverse door closing. I'm sure Chamberlain works basically the same way. The colored (visible) lights are to aid in setup (aiming), and for verifying operation.

Posted on Apr 29, 2010

Testimonial: "seems sensible I'll have to check it out further when I've got some time this weekend Thanks"

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My garage door opener is a 3/4 craftsman and one light is yellow and the other is green. I put my hand in front of the green light and the green light went off. the other side is a yellow light and it


Hi Vickie,

The safety beam portion of the garage door opener is set up to stop the door from closing if something (car, person, etc,.) is in the doorway.

When the door is open - if you press the hard wired push button (not the wireless remote) the door will either close until shut completely, or begin to close and reverse direction as soon as you let go of the button. When this happens, it *usually* means that a sensor is blocked - and reversing the door motor. If you try yhtis with the remote the door may not move at all or just bump down and stop.

You should re-align the sensors as described in the link below. Good luck!


How to Replace the Safety Sensor for Garage Door Opener Repair Guide Help...

How to Adjust Photo Eye on Garage Door

Nov 03, 2014 | Craftsman Professional 3/4 hp Hydro-Glass...

1 Answer

How to get my garage door to open all the way?


Three blinking lights & door won't close by Candi
(Winston-Salem, NC)
Garage door will not open and close with remotes. Three blinking lights occur when we try to close door. What does this mean? It is a Linear unit.

I will assume you mean that your garage door will open with your remote but will not close. It should close if you press and hold the wall control button until the door is fully closed.

If that is the case, the 3 blinking lights indicate that your garage door's infrared safety beams are not properly aligned.

1) Check that the operator has power. The green lights on the sender and receiver should be lit.

2) If the receiver's green light is on, but the red light is off, the receiver has power but is not detecting the infrared beam from the sender. The red light might flash when the beam is partially detected. This can be caused by
mis-alignment or something blocking the beam.

Adjust the safety beam sender and receiver while watching the receiver's red light (stay out of the beam while aligning it). When the red light stays on, the beam is aligned and your garage door should operate normally.

http://www.linearcorp.com/pdf/manuals/LCO75.pdf

NOTE: If the receiver's red light remains off, check for:

1) Dirt on the receiver's lens,

2) Sunlight shining into the receiver's lens,

3) A short in the safety beam wiring (from staples or at the operator terminals).

Jun 15, 2014 | liftmaster Garage Door 1/2 Hp

2 Answers

The light on the Garage door blinks but doesn't stay on.


Three blinking lights & door won't close by Candi
(Winston-Salem, NC)
Garage door will not open and close with remotes. Three blinking lights occur when we try to close door. What does this mean? It is a Linear unit.
I will assume you mean that your garage door will open with your remote but will not close. It should close if you press and hold the wall control button until the door is fully closed.
If that is the case, the 3 blinking lights indicate that your garage door's infrared safety beams are not properly aligned.
1) Check that the operator has power. The green lights on the sender and receiver should be lit.
2) If the receiver's green light is on, but the red light is off, the receiver has power but is not detecting the infrared beam from the sender. The red light might flash when the beam is partially detected. This can be caused by
mis-alignment or something blocking the beam.
Adjust the safety beam sender and receiver while watching the receiver's red light (stay out of the beam while aligning it). When the red light stays on, the beam is aligned and your garage door should operate normally.
http://www.linearcorp.com/pdf/manuals/LCO75.pdf
NOTE: If the receiver's red light remains off, check for:
1) Dirt on the receiver's lens,
2) Sunlight shining into the receiver's lens,
3) A short in the safety beam wiring (from staples or at the operator terminals).

Dec 02, 2013 | liftmaster Garage Door 1/2 Hp

3 Answers

Garage door light blinks but doesn't stay on


Three blinking lights & door won't close by Candi
(Winston-Salem, NC)
Garage door will not open and close with remotes. Three blinking lights occur when we try to close door. What does this mean? It is a Linear unit.

I will assume you mean that your garage door will open with your remote but will not close. It should close if you press and hold the wall control button until the door is fully closed.

If that is the case, the 3 blinking lights indicate that your garage door's infrared safety beams are not properly aligned.

1) Check that the operator has power. The green lights on the sender and receiver should be lit.

2) If the receiver's green light is on, but the red light is off, the receiver has power but is not detecting the infrared beam from the sender. The red light might flash when the beam is partially detected. This can be caused by
mis-alignment or something blocking the beam.

Adjust the safety beam sender and receiver while watching the receiver's red light (stay out of the beam while aligning it). When the red light stays on, the beam is aligned and your garage door should operate normally.

http://www.linearcorp.com/pdf/manuals/LCO75.pdf

NOTE: If the receiver's red light remains off, check for:

1) Dirt on the receiver's lens,

2) Sunlight shining into the receiver's lens,

3) A short in the safety beam wiring (from staples or at the operator terminals).
http://www.linearcorp.com/pdf/manuals/LCO75.pdf

Dec 02, 2013 | liftmaster Garage Door 1/2 Hp

2 Answers

Door suddenly will not close without holding the button down continuously that is inside the garage. The remote button will open the door but not close it. The door starts to close and stops right away.


It definitely sounds like a sensor problem. In normal operation, one sensor will have an amber or yellow light on, indicating power to the sensing circuit. The opposite sensor should have a green light on. If the yellow light is not on there is no power to the circuit due to a broken wire or circuit board failure. If the green light is not on or is flickering, the sensors are not aimed at each other or the light path is blocked.

Aug 04, 2011 | liftmaster Garage Door 1/2 Hp

1 Answer

My garage door will open just fine, but when I try to close it the light blinks 3-5 times and then I have to press to button and hold it until the door closes completely. what can be the issue?


Check the obstruction sensors and for anything blocking the doorway. If both sensors do not have the appropriate lights on, adjust them to get the beam across the doorway to the opposite sensor. (My units have amber and green lights on different sides. Both lights must be on.)

I hope this helps.

Cindy Wells
(we often get the sensors out of alignment when someone walks too close to the rail of the door. Weeds and bright sunshine can also interrupt the light beam.)

Jun 27, 2011 | liftmaster Garage Door 1/2 Hp

1 Answer

The door will open just fine, when closeing the door (by the wall switch) it will not close unless you hold the buttom down. The sensors at the bottom of the door has a green light on one side nad the...


Your door switch is bad. You can get one at home depot, it's nothing more than a door bell button. Your lights are correct and I bet if you try to close with your remote it works. That also will verify it's a bad button.

Mar 01, 2011 | liftmaster Chamberlain Garage Door Opener...

2 Answers

DOOR CLOSES MOST OF THE WAY AND THEN OPENS. LIGHT THEN BLINKS TEN TIMES. I NOTICED THAT ONE SAFETY SENSOR IS GREEN AND ONE IS YELLOW. PLEASE ADVISE.


Hi. The sensor with the yellow light is telling you that it is miss-aligned, Usually it only takes getting bumped to knock them out of alignment.
I would slowly turn or adjust the positioning of the sensor.
The one with the yellow light should turn green when it is all the way in line so that the beam is completing it's path.

It's out of adjustment, so the sensor is looking at it like there is an object blocking the door from closing.
It's called the obstruction sensor.
It's there as a safety feature, so that the door doesn't come down and smash anything in the opening.

I hope this helps you out.

Feb 04, 2011 | liftmaster Garage Door 1/2 Hp

1 Answer

We have a 1/2 hp garage door opener and it is blinking 4 times. it will shut with continuous pressure on the button but not with a single press. the sensors are different, one has a continuous yellow light...


The most common reason for the green sensor to flash is because they are not pointed directly at one another.

  1. Check each sensor for a steady glowing indicator light. If both indicator lights are on, or if one indicator light is flickering, the sensors may be slightly misaligned. To check for misalignment; obstruct the beam of the sensors so that they cannot see each other. When the beam is blocked, the indicator light on one of the two sensors will temporarily go out. This is the receiving sensor. Remove the obstruction and loosen the wing nut on the back of the receiving sensor. Adjust the receiving sensor until the green indicator light goes out, if not already out, then realign until the green light is bright and steady, then retighten the wing nut. This usually takes a couple of attempts before it is back in alignment.

Jan 01, 2010 | Sears Craftsman LiftMaster Chamberlain...

2 Answers

Remote does not open or close garage door; inside button flashes


What has happened is that you electric eyes are blocked or have gone out. The eyes are at the garage door about a foot of the ground on both sides. There should be a red or green light on one of them. If not some thing is blocking the beam that goes across the door. It is a safety beam so kids can nt get hurt when the door is coming down. If the beam is broke the door will go back up.

Jan 24, 2009 | Chamberlain Powerdrive PD422D 1/2 HP...

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