Notice the line (Main Power Rail). In older laptops, B+ just went straight to the CPU buck converter. On the LA-C781P, trace the B+ line to PQ100 and PQ101 (the isolation MOSFETs).
"Always-on" rails required for the Super I/O and BIOS. +1.35V: Dedicated power for the DDR3L memory modules. +1.05V_VCCST: Sustained voltage for the CPU. +VCC_CORE: The main power supply for the processor. La-c781p Schematic
Let’s break down why this particular schematic has become a legend in the repair community. Notice the line (Main Power Rail)