Hello, I have a problem with a Liftmaster 1040-6 Garage Door Opener. All of the sudden it stopped working due to a humming sound. I am pretty sure it's not the door because the same thing happens when the chain is disengaged from the unit.

I searched the net and a common cause of this seems to be a faulty capacitor, so we replaced it. Same thing.

Then we noticed that the base plate that is attached to the motor and the worm gear 'jumps' about 1/8" as I press the open or close switch. The end result is that the worm gear won't engage with the main gear. If I hold the base plate down so it won't jump then the motor will actually run!

Then we noticed the gear was worn so I ordered the kit and replaced it as well. Still won't work properly however.

As a workaround, I actually made the unit work by placing a long screw in a way that will keep the base plate from jumping. At this point I managed to get the garage door opener working again.

But I am not comfortable with this, it's not the way it's supposed to be and could be an indicator that something else is faulty. I suspect the worn gear is really a result and not the root cause of the problem.

Just to be sure, I tested the safety reverse mechanism and it all works as it should, after a few adjustments.

So again what I am trying to find out is, what could be the cause of this base plate/worm gear jumping just enough to not allow the gear to move?

Thanks in advance