I have just completed a worm gear replacement on a craftsman 1/2 hp GDO. After assembly the door will only travel a short distance before going right back to its starting point (with chain on or off). I have adjusted everything on the opener but still have the same result. Would the RPM sensor have anything to do with this? Safety sensors on the door are working properly as well.

If the remote and keypad both quit working at the same time you have a receiver problem. The receiver is part of the logic board and that needs to be replaced.

jiyu - If it is the remote you can buy a replacement and it is easily programmable. My mother has a Craftsman 1/2 HP unit like this, which is actually made for them by Liftmaster, and if memory serves there should be a button where the wires connect to the unit that states program. Press that button at the same time you press the button on the new remote until it starts flashing and the remote should be programmed. This may not be exact, but there should be instructions with the new remote and if not have Sears pull out a manual on one of their openers. Also my mother has a switch on the wall that looks like the remote and one of those 3 buttons has a lock symbol, that locks out the remote, so that no one from the outside can access the unit with a remote. She accidentally pressed that button by mistake and her unit stopped working, so you may want to check that on the wall and remote. The light problem you mentioned could be a sign of a more serious problem. Good Luck!

open it up and check for a broken wire to the light. if the wiring and light socket are good, then you likely have a bad logic board. check the wires for voltage when the light should be on. if the wires have voltage but the socket itself does not, then there is a problem.