Make sure you don't have problems with the wiring on the docking connector (wires inside the player going from the connector to the motherboard), make sure you don't have a loose screw rattling around inside the player shorting out components. Make sure the docking connector itself is tightly screwed down (it has special screws that allow it to wiggle even when the screws are tight).

You are right that it is unlikely to be the AC connector. The problems with that connector usually manifest themselves as the player not properly sensing its home/car mode.