12v power plug not working

Hi, I have an Arduino Due board that worked fine when new. I can't get the board to power up using the A/C adapter. I tried replacing the 3.3v voltage regulator with no improvement. Can someone tell me where I can find a good wiring schematic to troubleshoot this? I have looked everywhere on the internet looking for a diagram showing the boards components. Thank you for your help.

Google “ Arduino due schematic” it’s the first or second hit ...

Thank You!