Question about liftmaster Chamberlain Garage Door Opener Transmitter 300MC

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When button is pressed, nothing is blocking the sensors, but the light is flashing on and off

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First check the alignment of the eyes.

Use the pull cord and disconnect the opener from the door. Operate the opener and let the carrier slide back away from the door. Is the carrier moving smoothly when disconnected? Next, lift the door by hand from the bottom to the top. Is it moving smoothly? If not, lubricate the axles of all the rollers on both sides of the door. Check the cable pulleys at the top sides of the door channel, lubricate them as well. Are all cables in all the pulleys, there are 4. After checking those things, there is a "up force" and "down force" adjustment on the opener, try increasing the "up force" by turning the adjustment in the direction of MORE force.

Posted on Jan 03, 2011

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Posted on Jan 02, 2017

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Craftsman 53918 - 3/4 hp, belt drive garage door opener. Wall unit says safety sensors misaligned. Replaced them as suggested by manual, no fix. Does not appear to be any power from where you plug...

The main light flashing 10 times is the sign of a door sensor problem. Check to see if the small light on each sensors is lit and not flickering. If you cannot get both lights to come on your sensors or the wiring to them is bad.

Sep 30, 2010 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

Garage door opener won't close, light on unit flashes

Easy problem - and easy (temp) solution.
The safety pet sensors are blocked or broken
Press the button in the garage and hold it until the door is completely closed.....this over rides the safety sensor at the base of the garage door.
You cannot over ride the sensor with the wireless remote.
Check to be sure that the sensors are pointing at one another.
If they are, check the wires.
If good, the sensors have gone bad. Order replacements.

Mar 21, 2010 | Chamberlain 950CB Remote Control

1 Answer

Door opens, when closing stops immediately but there is nothing blocking the safety light and lights are green. I can hold the button and door will close but as soon as i release the button it opens again.

Check your door sensors closely. Sometimes one will be off just a bit and the light will be on but blinking ever so slightly. If the main light flashes 10 times when the door reverses it is definitely a door sensor problem. Nothing else will cause that.

Nov 23, 2009 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

Okay, I'm having an issue with my Sears Craftsman garage door opener. Not exactly sure of the model number, but can dig it up if that's necessary. Symptoms: 1) Door opens fine from either wall button or...

It sounds like you have a problem with your wall button. I would remove the button from the wall and then disconnect the 2 wires on the back. Remember where they go as they are color coded. You can then momentarily touch the two wires together to check the operation. There isn't enough voltage there to bother you.

One thing to remember. If when the door reverses the main light flashes 10 times it is a door sensor problem and nothing else.

Sep 23, 2009 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

Door goes up when I press the button, but not down

If when you close the door the main light flashes 10 times and the door reverses to the open position it is a door sensor problem. Check to make sure the small light on each sensor is lit and not flashing. They must be pointed at one another to work properly.

Jul 30, 2009 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

When we push the button for door to close it moves an inch and the light blinks several times. if we hold the button the door will close all the way. there is nothing blocking the floor sensors and the...

Most likely one of your door sensors has been bumped and is misaligned. Check to see that the small light on each sensor is lit. The only thing that will cause the main light to flash 10 times when the door reverses is the sensors or the wiring to them. They must be pointed at one another for both lights to be on.

Jul 12, 2009 | Sears Craftsman LiftMaster Chamberlain...

2 Answers

My garage door wont go down.I habe to hold the switch down but if i let it go the door will go up again.

I have a Liftmaster garage door that won't go down unless you press and hold the wall button. The sensor lights are both on. The green light on the unit flashes unless I press the reset button. As soon as you press the wall button it flashes again and the door won't go down unless you hold the button the whole time. The remote wont' make it go down either. It begins to sometimes and retracts, but sometimes the light bulb just flashes (like it is obstructed). I tried replacing the wall switch and that did nothing. Help!

May 16, 2009 | Sears Craftsman LiftMaster Chamberlain...

1 Answer


Check your cartridges are good, must be sat correctly.

check that the timing strip is in the center

1. clean **** strip film
2. clean **** strip film sensor
It is located at the back of head carriage, use a contact cleaner.

check something is not blocking the carriage.( usual suspect )

To reset
1. Turn off printer
2. Hold down Resume button and press Power button.
3. Keep holding down Power button and let Resume button go.
4. Press Resume button 2 times then let BOTH buttons go.
5. Green lights will flash and then stop blinking.
6. When green lights are solid, press the Resume button 4 times.
7. Press the Power button and the printer should turn off, if not,
press the Power button once more.
8. Your printer should respond as normal..
Or, press reset( or resume) button 4 times then power.

Hope this helps

Apr 21, 2009 | Canon Office Equipment & Supplies

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