Are the two boxes the same models? If not, then swapping parts may not work. If they are the same model then I would start by swapping out the power supply first. That doesn't require any soldering. You might also swap out the hard drive. I can't say for sure that the hard drive would cause the bad video but it could if the "live buffer" that gets recorded is what you are viewing. Another thing to try is to see if the feedthrough RF port on the Tivo has good or bad video. It should go directly into the Tivo and be split off to go out again. Also, have you tried using a different set of output ports from the Tivo (e.g.: the S-video instead of the composite)? Good luck.