How the rrod happens is that from turning the xbox on and off so much the solder expands and shrinks until the connection isn't made. So they install the thermal pads to reflow the solders. If you do it in the oven it fixes it a lot better.
The same idea is used when your xbox stops displaying picture, but plays sound through the TV.
The same idea is used when your xbox stops displaying picture, but plays sound through the TV.