We have a Model 139.53525SRT 1/2 HP . We recently had the springs replaced, had been working ok. We have had the partial opening then going back up with the light flickering situation, which I guess was an optical sensor issue. Most recently, occasionally the door was going down too far and bouncing back open. Now it simply buzzes when you hit the opener, nothing moves, the buzz pauses briefly and a second buzz happens again and nothing moves. It seems to me we had this happen a few years ago, too, and we got it going again, but we can't remember what it was. Seems playing with the sensors, lubricating the rails or flicking the switches have gotten going again in the past. Warmer weather helps, too. Suggestions welcome. Haven't looked up in the gear / sprocket area too close yet. We have the manual ... seems overtravel might be an issue / jammed into stop bolts it suggests

Ok, had some free time yesterday and spent a few hours trying to fix this darn opener. I now got the opener to go all the way up, but it still won't go down more than 6 inches. What I do is trick it by hitting the button on the remote and then hitting it again when it is about to reverse. I do this over and over until the door makes it all the way down (what a pain), then I adjusted it perfectly to stop once it goes all the way up. What I did to get it to go all the way up I'm not even sure. I messed with all the wires to make sure nothing was loose or disconnected, everything was fine though. I just kept playing around with everything and poof, all of a sudden the sucker was going all the way up. Now I need to figure out what to do to get this thing to go down. I have tried over and over using the down force and the other down adjuster, but it does nothing to help this problem. I'm hoping one of you guys will know what is causing this now that I at least got the door to go up fine. Thanks!

Your first problem sounds like the door is hitting the floor and the safety is reversing it to the open position. Adjust the 'down limit' on the side of the opener about 3 or 4 turns in the opposite direction of the arrow printed on the cover. This should cause the door to stop short of the floor. Now you can adjust to just close the door. Your second problem is what you suspect. Your door position is out of sync with the chain position.

just found this thread as I am in the market for a new garage door opener. My 8 year old screw drive opener (craftsman 1/2 hp) is fine, except it just lost a circuit board from lightning and power spikes. The repairman (Overhead Door) also replaced the pulleys while he was here. It opens a lot smoother now with the new pulleys. My 25 year old Craftsman 1/2 HP chain drive opener is in need of replacement (motor died). My Overhead Door dealer doesn't sell screw drive openers. So now I need to get a new one for that bay. decisions... decisions... I'm tempted to go with Craftsman 1/2 HP again, but I don't see the screw drive choice on their website. As far as the OP goes, probably a 3/4 HP would solve that problem. I would think that the HP would be more important than the chain or screw drive or belt style factor -- or who installs it.