Question about liftmaster Chamberlain Garage Door Opener Transmitter 300MC

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Lift-Master GDO goes up, not down

1/2 HP Lift-Master GDO. No recent gear replacement or adjustments. Door started to fail to go down. Adjusted down sensor to max, no effect. Electric eye operation is normal. No evidence of gear shavings inside, RPM sensor seems to be working correctly. (When I disconnected it, it failed differently)
Door will come up just fine once down. Even when I disconnected trolley from door, trolley only moves about 12 inches, then reverses. LED sensor flashes 4 times. Any hints?

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If the door operates freely without any binding, while operating it manually then It would appear that the obstruction sensor mounted across the doors path is ether out of alignment, lens dirty,or malfunctioning

Posted on Feb 22, 2009

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It sounds like the gears are stripped out when the door is trying to come up

It could be. As I recall, the gears are nylon composite gears so they could be stripped out.

First, check the force adjustments to be sure they are adjusted correctly. If the UP force is not adjusted properly, the mechanism could be slipping and the door not opening. Try adjusting it to see if the door will open and close properly. The DOWN force adjustment is for making sure the door seats properly and should not impact the door closing unless you have it set too high, in which case it could be trying to exert excessive force on the door when closed.

If these simple fixes do not work, look at the owners and parts manual you received with the opener, or check on line to see the exploded parts manual page from Chamberlain and see if the gears are available before you attempt to dismantle your opener. If you don't have experience in mechanical repairs, or the opener is old, it may behoove you to purchase a new opener on sale with a new warranty.

Usually, gears that strip are from a door that is too heavy for the opener, an opener that is of insufficient power for the door, a door that is not properly adjusted and places too much strain on the opener, or an improperly adjusted opener.

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1 Answer

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I would say you got your money's worth, I would suggest just replacing the opener.

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It's a 7' high 5 panel door controlled by a lift master .5HP opener. It stops when the top roller hits the curve in the railing. I've cleaned and lubricated the hinges, and cleaned the tracks. The...

Sounds like a broken spring??

If you have a torsion spring look for a gap in the spring.

I would have it replaced by a professional - it can be dangerous.

If the spring is OK it probably need to be adjusted or the opener needs adjusting.

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1 Answer

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1 Answer

The motor makes a noise but seems locked up. 2265R Chamberlain lift master professional 1/2 hp

Make sure the door is running well with out the openers help first of all. If it is making this sound then look inside the unit with the unit unplugged for white shavings. If so you will need to replace the gears. Thanks BB

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My liftmaster garage door only opens 8 inches and then stops

It sounds like the opener is stopping because the weight of the door is tripping the lift sensor on the opener. There are two screws on the side of the opener to adjust the lift and close pressure. Find the lift pressure screw and ajust it higher to see if that remedies the problem.
Also, because you said the door will not stay open at the top when you open it manually, I think your springs are not adjusted correctly. They should hold the door open in the up position when not connected to the door opener. That may be the reason the opener lift pressure is kicking it out.
If you have to adjust the springs, be careful that you know what you are doing. There is a lot of potential for getting hurt if you don't know the proper proceedure.
Good luck.

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My Liftmaster Professional 1/2 hp unit opens to the correct limit, however, after it stops, it starts to slide back a few inches, the motor engages and pulls it back up, it slides, it pulls it back up,...

there are internal limit switches that look like little plastic wheels on a screw. if these wheels dont push the buttons in on either side as it travels it will try to keep traveling see if you can locate these plastic wheels and the switches they push in both the full up and full down position and make sure they are actually pushing the levers

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1 Answer

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The motor will need rewinding, and the condensor will probably need replacing.
That should do it:)

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1 Answer

Liftmaster gdo won't operate with door or remote

Hi there, when the problem first started was the door being used frequently? If your GDO was used quite a few time's in a short period of time the "overload" may have triped. The makers of all GDO's now adays install an overload witch is an electrical safety device protecting the motor. This prevents over heating in turn burning up the motor. To rectify unplug for 15-20 mins. If you have Model number 1270 turn to pg. 7 in owners manuel. Insure all door locks are free. Insure power to electrical outlets by pluging desk lamp in same out as GDO. what model do you have?

Mar 17, 2009 | liftmaster Chamberlain Garage Door Opener...

2 Answers

Grage door reverces and goes back up after touching the ground

try adjusting the close shut off switch.(limiting switch) It sounds like when the door shuts, it has too much pressure. The sensor picks this up and reverses the door.This is a saftey feature. It just needs adjusting

Mar 06, 2009 | liftmaster Chamberlain Garage Door Opener...

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