One additional thought: The 7904A is newer and easier to access stuff to fix. The upper and lower chassis hinge apart. I would hunt down the 15v short and fix that one first and see how the unit works. As a newer unit, it might be in better overall condition. Also, check if it has the boxer fan on the back or if it has the older tek custom fan inside. The boxer fan units were the very latest production. I have one of those and it looks brand new all over.
Reinhard Metz
