I have an older model (no sensors) Craftsman 1/2HP garage door opener. Any time I attempt to close the door, it activates and closes a few inches, then will trip and open back up. I noticed that there was quite a bit of slack on the chain, so I adjust it so it would be a little tighter but that did not solve the problem.

Somewhere your garage door is binding. Since it jams when closing, I would guess the loose chain was on the side that pulls the garage door open. Before the light sensors came out, the openers were designed to detect any binding, and interpret it as a possible object in the door’s closing path, which would then cause the door to open up again.

The gondola is the little thing that glides along the track. I’m assuming you do not have a screw-drive. The opener bar is attached, one end to the gondola, and the other, to the garage door. It (the gondola) needs to slide smoothly along the track. Then there’s the door wheels. Or do you have a 1-piece pivoting door, typically found in areas where there is no snow?

Did you recently adjust a spring or door track? Maybe someone hit the door or track. There are also a couple of screws on most of the opener units, which allow you to adjust the opening and closing force.

Try pulling the emergency handle to disengage the opener from the door. Then open and close toe door manually and see if it sticks anywhere. You can also try to consult your manual for more troubleshooting tips, if you still have it.

It could also be something internal to the unit, in which case it would probably be cheaper and easier, in the long run, to just go buy a new unit.

TomR is right on the money. I'd just like to add a suggestion (I have the same setup), oil the wheels on the door. In my garage I tend to have to oil the wheels once a year or so. Be sure to oil both the wheel and the shaft, this will allow the wheels to rotate freely and not bind. Good luck!

I have the same problem with my older unit, Model 139.53606 serial # 5061A0D272. At first oiling the wheels helped, but lately it does not work. Try pulling the emergency release and hit the open/close button. Does the motor run and move the chain longer than before? On mine it does not. I believe my problem is electrical, and inside the unit is an optical coupler mechanism that senses when the motor is turning. On the end of the motor shaft is a plastic encoder wheel which rotates between an LED and an optical sensor (probably an opto transistor). If the shaft is rotating the light beam is repeatedly broken causing an alternating signal on the opto sensor. My guess is that if this signal in not present, the circuit assumes you door is jammed, or the motor is stuck, and shuts off the motor power to keep it from burning up. Do you have an electrical diagram or schematic of the unit? I don't even have a manual.