Laptop boots to an external monitor, but internal keyboard/trackpad do not work. Schematic Section to Study: EC (Embedded Controller) I/O lines (Sheet 5 or 6). Common Culprits:
This is the hardest part. Motherboard schematics are copyrighted and not officially distributed. However, the repair community shares them. la-h103p schematic
Finding the is the "Holy Grail" for diagnosing board-level issues. Whether you are dealing with a laptop that won't power on, a "plugged in, not charging" error, or a short circuit on the main rail, this technical document is your roadmap. What is the LA-H103P? Laptop boots to an external monitor, but internal