are the regulators on heat sinks??? they must be on heat sinks and mounted with heat sink grease or sil-pads. if they have metal tabs, either the 79xx regulator needs it's own heat sink, or it needs an insulating washer on the mounting screw. the tab is connected to the output pin of the regulator, and the 78xx tab is connected to ground. so if they're on the same heat sink, the 79xx needs to be electrically isolated from the heat sink, while still thermally coupled to it