Sears Craftsman 1/2 HP garage door goes all the way down, then back up. The lights do not blink. Checked for obstructions, none. Nothing blocking the sensors. What can I do to fix this?

The dial is the force adjustment. if it ever does it again and the light on the opener isn't blinking, its a bad rpm board

Check the resistance down button (There is one for down and another one for up). You may need to adjust the sensitivity. That way even if for some reason the have hard time coming down, less sensitivity may solve that issue.

you may need to adjust limit switches in back of operator.Most of the time with this problem one of the gears inside the operator has stripped out.

Check your door springs. Could have a broken one. Also remove the cover from the motor unit and check the drive gear. It could be stripped. If the light on the back is blinking randomly that is normal. It can also send a code. See if it blinks a number of times, pauses and then repeats.

if the stops are not wrong.
they tell it how far to go up and down.

then I think the safety sensor is misaligned.
make sure the light on one side is pointed at the receiver on the other. maybe it is dirty or blocked.

good luck!

I have worked on a few garage door operners. Sometimes the solder breaks where the metal maked contact. Could have it checked or may need a replacement from Sears.

If the main light blinks 10 times when you try to close the door it is a door sensor problem. Make sure the small light on each sensor is lit and not blinking. Tweak them a bit if necessary.

with the door down, disconnect with the emergency release, see if the motor operates
with no load...if the the track moves you probably have something obstructing the door
ie; a broken spring, door locks, etc ... the chain should be adjusted for just a little
**** mid way down the rail (1/4") if it still doesn't move ... call sears.

If you can press and hold the wall button and the door will go down, you have a photo eye issue. Check the photo eyes at the bottom of the door.

you did not give enough info. If it closes completely and right away goes up, if bulb blinking. if it is, something on door is blocking safety beam. If light is not blinking, DECREASE down travel.