Craftsman garage door opener not closing
I have a Craftsman 139.53615SR opener with a 41A3621 circuit board. No door sensors. No remote is being used (just the wall controller).
The door opens with no problem. When is push the button to close it, however, it travels 4" and stops. If I push it again, it travels 4", stops, and then goes back up 4". If I hold the button, it travels down as long as I command it, but goes back up as soon as I let go of the button.
The gears look fine and there is no plastic "sawdust". I've adjusted both of the travel dials and the force dials, with no effect. It behaves the same whether the traveler is connected to the door or not. Any advice is appreciated.