Here's my tale, and request for advice. I just installed a Craftsman 1/2 hp garage door opener. The installation went well and the door opened and closed smoothly. So I started working through the adjustments. The door reversed when I obstructed the safety lights. The door also reversed when a 2x4 was placed under it. In each case, the lights flickered as expected. While testing, I found that I needed to increase the up force to 3kg. And I adjusted the down distance a little.
My problem occurred when I adjusted the up distance. Now when pressing any button, the opener goes down about 6", then goes back the same 6" by itself, with no flickering lights. No further adjustments had any affect. I have worked the door by hand - it runs smoothly. I have removed the chain from the drive, without change. Could some circuitry have burned out while I was testing the door? I am at a loss and welcome any advice.