I'm trying to troubleshoot a garden variety Liftmaster. The chain sprocket broke so I replaced the sprocket assembly. Now the door goes down less than a foot, then comes back up. The kicker is that the light on the motor doesn't blink at all, like it normally does when there is something blocking the door sensors. The door sensor lights appear to be aligned and functioning correctly. I can't find any information about this. When I search it, every result that comes up is where the motor light does blink when the door won't go down.

Do not ever tie a loop or noose in the manual pull rope.

You’ve got the limit switch settings screwed up. Too tight.

https://support.partner.liftmaster....he-travel-and-force-limits-1484145519999

I would start here as well

I'm not familiar with the Liftmaster, but on some door openers, there is a knob/dial that adjust current settings. If the current draw is above a set point, the door try to close, but will reverse automatically after a foot or so. Sometimes just a dry chain and rollers on the door will cause the problem. Dry chain and rollers cause the door to be harder to open, thus increasing the current draw. Before you adjust anything on the board, take some chain lube and give the chain and rollers a good lubing.

Another common problem is the door was not positioned properly when the chain/sprocket is put on. Did you make sure the door was all the way open or closed, when you put the chain on. If not, the limit/proximity switches, that tell the door when it is open/closed, are not set properly and this could cause this problem.

There's more, but these are the 2 most common.

Thank you for the link and diagnosis Swifty52! I'll adjust the down force screw per the instructions in the link and hopefully that will solve the problem.

Not force screw, travel screw first

You will find there are experts of all subject matter on the 'Fire. It is the ultimate universal brain trust and some specific members know absolutely everything themselves. We are a blessed community. Cumbaya.

Correct, on mine you can remove the cover and see the operation. On the gear drive it’s practically impossible to get the thing back in the same position as when it busted which means the travel limits are way off. I had no issue with the torque.

I just got done going through this myself. These are my suggestions:

A. Make sure The garage door can be lifted and lowered smoothly and easily by hand by adjusting the torsion spring and the drum rollers. The drum rollers on each end have to be identical tension.

B. Make sure the travel limiters are adjusted properly.

C. If your Government-mandated safety item reversing sensors are mounted on the track, take them off and mount them permanently to the jam.

My sensors were mounted to the track, and when the door started to move they wobbled just enough to make the door reverse. Once I mounted them solidly to the jam using wooden blocks, the door worked perfectly.

Direct sunlight on one or the other eyes can stop the door.

Or, take them off and mount them to a paint stick about an inch apart on the rafter and pay attention that there's nothing under the door when you push the button.