Unfortunately, since the declination drive motor, encoder and all the rest of the system including the computer are part of a closed loop control system, it is difficult to find the problem without appropriate test jigs and procedures. Well, this should give all you mapuggers who have had runaway dec drives a chuckle. It has just happened to me. This morning I went to the Madison Astronomical Society site for our annual picnic. I got there two hours early to clean up the observatory and get the LX200 polished and running for Solar observation.
Nothing Turn it on and turn it off a few times.
Talk to it. Talk in no uncertain terms. Kick the pier. Kick the pier harder. Took off the dec drive cover and wiggled everything carefully.