Question about liftmaster Chamberlain Garage Door Opener Transmitter 300MC

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Door will not go down. Door seams to think that something is in front of the sensors. sensors are not blocked and are alined. Sensor was pulsating

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Try and disconnect the sensor from the opener and see if it works. If so, then it is your sensor(s). Just buy new ones if that's the case.

Posted on Feb 02, 2010


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Door goes all the way down, stops and then goes up again.

The problem is probably the opener safety sensors. Inspect the photo-eye sensor. The sensors are the small black boxes the near the bottom of your garage door frame which are usually installed on the tracks with a small bracket.
When the infra-red sensors are malfunctioning, usually one of the sensor lights will be blinking. The problem is either due to a blocked path between the sensors, dirty eyes, loose wires at the sensors or at the motor head, or just bad sensors. The transmitters (remotes) will not work to close the garage door. You will find that the door will only move an inch or so in the close direction and reverse. When this happens your garage door will only close by holding down on the wall button, or wall console, until the door fully closes. This method is the only way to override the safety and close the door.
1. Make sure that there is not something blocking the sensors from communicating with each other and the wire connections are securely fastened at the sensors and motor head, and the eyes are directed at each other. A lot of the time dust, spiderwebs, or even a small toy can block the sensors. If there is anything blocking the sensor remove it and try your door again.
2. If there is nothing blocking the sensors they maybe misaligned. They need to be pointed at each other in-order for they to work . If they are try to push alignment sensor into alignment. You will know they are aligned when the light stops blinking on the sensor.
3. Also, try unplugging the garage door opener and re-plugging the unit back into the outlet. This acts as a reset and may reset the sensors. If nothing works, it may be that you have to replace the sensors.

Jul 24, 2017 | Building Materials

1 Answer

Why does dooropener lights blink when butten is pressed

could be something blocking the sensor . My sensor on the floor on one side was blocked by a spider web holding a leaf in front of it. My door light would flash and door not go up or down. After i cleaned both sides every thing worked ok.

Jul 01, 2016 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

Door starts to close and opens back up

either something is binding the door which will make it think something is under it causing it to reverse. if its not hard to open or close there is a adjuster in the control panel that you can turn up or down to remedy the problem. if it is a newer opener the laser sensor may be blocked or out of alighnment

Mar 17, 2015 | Building Materials

1 Answer

Problem with AWO3561 wash machine red door light flashing

there is a valve for the door lock if this goes it thinks the door is open and shuts down thinking the door has been opened if the feed pipe become blocked the water pressure sends air pressure to the switch when water is added. spin/drain setting it don't use this sensor switch, but on filling up it will. its usual down to a blocked pipe , or a leak in the line. sometimes it can be the switch, the pipe is located at the bottom around 2 inches from the bottom and the feed wire goes to a sensor , take the pipe off and blow down it best to have some water in the bottom of the drum, so suck and blow on the pipe to loosen anything blocking the pipe. switch don't blow or suck on this as it can damage the sensor. if the sensor is at fault you can only replace it as the valve inside for the switch if you use anything it will pierce the valve , hope this helps you.

Jun 24, 2017 | Washing Machines

1 Answer

My HP CP 1518ni printer's alert says front door open but its not... is this a sensor problem.?

Hi there! You can easy check if the front door sensor is broken.Open the front door at look for a little hole in the right or left.In that hole you should see little metal lever.Take something thin and long and carefully push that lever.It should make a "click" sound.If the printer detects that the lever has been pushed down the message should go away.In that case the plastic that is located on the front door is broken and can`t push down the metal lever.Even after pushing down the lever the message is there,you need to open the printer and check if the sensor is working fine.If the sensor is working,then you have problem with your DC board and you need to replace it, which will cost you allot of money and time:D.So please replay if you have any other questions about something.Thank you for using!!!

Jun 22, 2011 | HP LaserJet CP1518 Printer

1 Answer

Need answer to opener #41A4315-7A replaced sensors door will not go down with remote. have to hold wall button down in order for door to come down all the way. when i press remote or wall buttton drive...

The wiring to the sensors must be right. If you notice the original wiring is color coded. One wire to each sensor is solid white and the other is white with a black stripe. I have a felling you miswired the right sensor.

Feb 19, 2011 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

Craftsman door opener. light flashing 10 times. must hold down the button to make it go up or down

There are 2 sensors that are near the bottom of the door tracks on either side. They have to "see" each other so it is likely that something is blocking one of them or one got bumped so they are out of alignment. Check to ensure nothing like a box lid or something fell in front of one of them then use the lights on them to line them up. Both lights should be on. Check to see if the door works at each step. If all this does not help check the sensor wiring for damage and if it has staples holding the wires to the wallboard it is possible that an errant staple is shorting out the wires to the sensor. Highly unlikely unless they have submerged in water a sensor itself may have gone bad. I hope this helps gets your door opener working. If this helps please vote yes, thumbs up. Thank you, Dean

Dec 12, 2010 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

The passanger side sliding door on my 94 Crysler Town and Country had been working fine, this morning however when my daughter tried to close it the door bounced back open, and now the door will not close,...

I think something maybe blocking it from closing check really well around the door and near the sensors. If that doesnt work i think a sensor went bad and now wants to stay open. Its like a position sensor tells the door how far to go and when to stop.

Sep 08, 2009 | 1994 Dodge Caravan

1 Answer

Cd door wont shut

this is possible but can lead to more frustration. The cd door usually has a plastic tab that depresses on a button or blocks the opto sensor to indicate it is closed. I presume that your cd door is missing this tab or the circuit that activates when the door is closed is faulty. Block the opto sensor manually using paper or keep the button depressed that the door tabe closes on. You will not need anything to keep door closed unless it is reqiured to play the cd then just use a brick

Aug 15, 2009 | GPX Karaoke Party Machine CD+G Portable...

4 Answers

Garage door only works partly

some thing blocking sensor or laser is not in proper alinement

Feb 18, 2009 | Sears Craftsman LiftMaster Chamberlain...

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