The adjustment for this is on the side of the unit. Use a small screwdriver and turn the 'down limit' in the opposite direction of the arrow printed on the cover.

If you have a wireless keypad and that also has quit working then it is definitely the receiver. Otherwise check to make sure the light in the wall control is not flashing. If so, press and hold the lock button for 3 seconds. You can find a manual at ManageMyLife.com. First though you need the correct model number. It is on the end of your opener nearest the door and starts with 139.

Read the instructions again and find and adjust the "travel limits". I think that will fix your problem. Also set the chain back where it was to begin with. HTH, Mike

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.