If your power brick light goes out when you plug it in, you have a short on the main 19V rail ( B+ ). The schematic helps you isolate which power stage (CPU, GPU, or WiFi) is pulling the voltage down.
It shows exactly how 19V from the DC jack is stepped down to 5V, 3.3V, and eventually the tiny voltages required by the CPU and RAM. la-g121p schematic
Modern motherboards are multi-layered puzzles. Without a schematic, you are essentially guessing. The LA-G121P schematic provides: If your power brick light goes out when