Sounds like a bad cap problem on the Composite, S-Video, Coax board. I would check that board for bad bulging leaking capacitors. The board is probably located at the rear inputs, the coax, composite and S-Video ports being physically attached to it, with the front inputs connected to it by wire. It could be that there are 2 separate boards for the Component and VGA inputs and the Composite/SVideo/Coax or it could be just two separate paths on the same board.
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