Top 20 liftmaster Chamberlain Garage Door Opener Transmitter 300MC Questions & Answers

29 years is along run on an opener. Personally I would replace it and not spend any money trying to repair it. You can try and find a control panel, or buy a new opener for $200.00 at HD. you can leave track in place replace rollers from new opener box.

It is probably the lubrication in the rollers. You should lubricate them and make a small adjustment to the torque sensor. When it gets cold the lub gets stiff. The torque sensor will detect this and open the door, a safe position.

batteries in remote maybe?

Try posting in the correct forum for better results

http://support.liftmaster.com/articles/How_To/LiftMaster-receiver-and-remote-compatibility-1484145638635 I don't believe a universal remote will work. Here is a link to compatibility

hi check that the door is free from stifness

This sounds like a similar problem that I had. The circuit board on the garage door motor has a capacitor that goes bad and this prevents the remotes from working. You can either buy a replacement circuit board online (for around $80 if I remember) or if you can solder, simply replace the capacitor for a few dollars. I answered a similar question on this site before after I went through the process. There are more details there. The capacitor in question was close to a heat producing component and over time it cooks.

Yes, follow the directions with your liftmaster, that should solve the problem.

Check alignment of the obstruction sensors .... they shoot a light beam across the doorway about 6 inches above the floor. One is mounted on each side of the door track near the floor.

It will only take a 4 digit program code. After you program the code, and then enter that code to open the door, hit an additional number on the keypad. Some need the additional digit to act like an 'enter' key.

Disconnect power to the opener! Then, with a dental tool or small screwdriver scrape off any corrosion etc from the contact in the center of the socket. Also note if it is lying flat against the bottom of the socket. If so, gently lift the center so it has some spring retention and rises up off the flat bottom of the socket.

Try connecting transformer to your other 115 volt line

Sounds like loose connections. Unplug, remove the cover and be sure all connections are tight and secure. While doing this be sure there are no burnt connections or burns on the PCB. Replace cover, plug in and it should be OK.

Your answer is in the last line, unless you have those lights, the opener assumes something is in the way. Make sure you have the green one pointing in the direction of the local sunsets as this is also a problem certain days of the year.

this is likely a force setting issue, with all the humidity the door might be getting more stiff, on the back or side of the unit there should be a screw it adjust, or you can reference the manual, but before doing so you should release the door from the opener (handle on the trolley) and check to see just how stiff the door is, if the spring has broken you will have to get a door guy to fix it.

One should be green and the other amber - The amber one stay on all the time, the green one tells if the alignment is OK or not (solid green means OK) Hope this helps, if it does please click 'helpful below'

That is the quickest way to get one that works.

Hi Laura: Mine does this too. I just thought that it was supposed to do this as it made sense to me. The light automatically turns off after a few minutes, so if the sensor indicates that someone is walking in and out while the door is open, the light stays on. I'm thinking........... It ain't broke..... don't fix it.

If it's just off a little you can adjust the limits. If it's off alot you need to take the gear set back out and set the belt / chain / screw to the closed position. run the operator to the closed position and then install the gear set.

The most likely cause of this problem is that the door is unexpectedly hitting the ground before the shut off of the motor. It is possible that the door is also jamming which makes the unit think there is an obstruction. If there is no mechanical problem with the door itself, you can make adjustments to the up/down force and the up/down limits. These adjustments are at your lifter motor unit and you should check or download your particular manual. I have linked a video showing the basics for this adjustment.https://www.youtube.com/watch?v=GebkW96Sd_c