Obtaining the correct schematic is the first step. The LA-H103P is a popular board, and its files are available from several resources, both free and paid.
The primary power rail generated directly from the AC adapter or battery. It distributes voltage to all major step-down switching regulators. la-h103p schematic
Once you have mastered the basics, the schematic allows for more complex troubleshooting. Obtaining the correct schematic is the first step