I have never seen a windlass with and up and down separate motor but I have not seen every windlass. The units I usually work on have a reversing solenoid that turns the motor in opposite directions. It is possible the solenoid is bad but also possible there is a loose, corroded or bad connection on the one side for down. I would start checking wiring and connections first. Remove them one by one, check the connectors, and clean both the connectors and the attachment points. Be sure and check the same on all switches if you have them at the helm and if you have foot switches. If this does not resolve the problem the solenoid should be checked next. A simple way to do that is to reverse the wires and see if the problem now trips the breaker in the up position. If it does then you need a new solenoid. If not then the problem lies with the motor. Good luck