A collector gave me this engine and tender that was still in the original box. Don't think it has ever been run. When I put it on the track the engine headlight comes on, it hums, but it will move only a fraction of an inch and stop. It acts like the wheel links may be out of sync....like when the pedals on a tricycle are not in position for the riders feet to push the pedals forward or backward. I took the shell off the engine, then removed 2 screws from the pan between the wheels but cannot determine who to get into the guts of it to see if the electrical connectors are contacting the wheels. Any thoughts?