Dell 1815DN Displaying Door Open Front Door or Fuser Door Open Error

If your Dell 1815DN is displaying "Door Open Front Door" or "Fuser Door Open" even though the front and rear door are closed, you should replace the High Voltage Power Supply. The HVPS contains most of this machines sensors and switches which can go bad causing these errors.
Dell 1815DN High Voltage Power Supply:  Part# - WH773.