Anytime you try to close the door the main light flashes 10 times and the door reverses to the open position it is a door sensor problem. Make sure they are pointed at one another and the small light on each one is lit and not flickering. Tweak them a bit. If you cannot get both lights to come on you have either a bad sensor or the wiring to them is bad.

I've read my situation over and again, but have tried all suggestions. I've changed the worm gear and sprocket with no problems. Now the opener goes about 1 foot one way and reversed itself back to the start point. The assembly on the shaft is taught. The black plastic rotary wheel rotates with no problem thru the sensor. I guess my next step is to buy a new sensor. Just not sure how this would have gotten damaged. It wasn't touched while replacing the gears other than removing the wires plugged to it. If there's a reset button or any suggestions for a fix, I'd be greatly appreciative. Thanks,

Make sure you put the black cup back on the end of the motor shaft and that it is pressed all the way on. Make sure the RPM sensor is plugged in. If neither of these are the issue, then you probably did not have the motor shaft pushed all the way back when you tightened the coupler after replacing the worm gear. Loosen that coupler up and from the front of the motor (opposite end in which the coupler is on) push the shaft back as far as it will go. Hold it there while you tighten the coupler back up and then try it.