The motherboard schematic for Asus X53U
PBL60 Mainboard – Compal LA-7322P
CPU: AMD Brazos APU + AMD Seymour-XT
Chipset: Hudson M1
OEM: Compal Electronics, Inc.
Motherboard code name : LA-7322P
Document Number: LA-7322P
NO POWER ASUS X53u
PU301 – RT8205LZQW
Near PU301 you will find 3VALWP and 5VALWP.
Those voltages are always on even before power button its depres.
To check them you need to probe on PL303 for 3VALWP and PL305 for 5VALWP.
If you got a short with ground reference the lift the coil in question and see where the short is located. inject 1-2v with max 1amp to located the faulty component.
Maybe problems where found on the B+ or B++ with mosfets that where connected to ground or SMD caps.
Check the main BIOS if there activity on pin 1,2,3 and 7.
On oscilloscope it will show even if power button its not press, only with adapter connected.
If those pins got flat line on oscilloscope showing constant +/-3.3V without any activity, reflash the bios using an external BIOS programmer.
After flashing the BIOS with the right image activity must be on those pins with only adapter connected.
Sometimes the BIOS IC may be broken and it will show only when Verify its operation its done on the chip. Replace the chip with same model.