Dead RTX 4090 gets cooked beyond salvation — VRAM swap and multiple signal patch jobs fail as buried PCB traces give up for good in unsuccessful repair attempt

A lifeless RTX 4090 with 48GB of VRAM landed on a repair bench, showing no display output. What followed was a deep dive into diagnostics, power rail checks, and trace hunting-only to reveal hidden PCB damage so severe that even expert fixes couldn't bring the GPU back from the dead.