He may even be best to disconnect the USB input outright - internally ( no harm if its already out of warranty, but if you're going to try it, TURN IT OFF FIRST AND DISCONNECT IT).
Some of these inputs are faulty - thats what i found in my case anyway and thats what i was told by the geek. This remained the case even after he installed another brand new input/dock, but it still didn't work even when its internally illuminated outline made it appear as though it was functional.
