sears 1/2 horsepower garagedoor opener

[elk4m3]

Problem originally started when worm gear needed replaced. I replaced the worm gear and then garage door would only open or close a foot either way. read the forums and checked I did not get the new assembly mounted down the whole way and rpm sensor wasn't seated deep enough. I reinstalled everything, new gear was seated at right depth, and rpm sensor was at correct location. Now the opener will run the whole cycle of the up movement, but it will only move a few inches on the down cycle and return to the up movement. The opener is sitting on my work bench and I am doing the testing there. If I undo the small clip holding the gear assembly and move the middle gear thread of the limit switch assembly the whole way to the down position and then reconnect the gear. When I start the opener it will go the whole back to the top on the limit assembly and stop as you would expect. When I hit the power again to have it reverse (close) it moves a little and returns back to the open position limit. I have also replace the rpm sensor along the way also. I am wondering if this is a problem on my logic board or am I missing something else?

[Helper]

Does this opener have photo eyes? If so you need to have them plugged in for the opener to finish the close cycle. If you are still doing the work on the bench you can simply use one piece of wire to jump the two photo eye terminals together to close the circuit.

[DixieDoor]

Does this opener have photo eyes? If so you need to have them plugged in for the opener to finish the close cycle. If you are still doing the work on the bench you can simply use one piece of wire to jump the two photo eye terminals together to close the circuit.

Bingo. Safety feature prevents closing (entrapment) but allows opening. Install a light bulb on the unit and once it refuses to close, it will blink a certain amount of blinks, a code in which you can use to determine the problem. Most likely find a sticker on the unit or its in the manual, but in this case it will most likely be informing you that the photo eyes are not lined up or installed properly. Good luck.