The schematic cleverly shows a "Back Drive Protection" circuit. If you inject 19V directly onto the main cap without consulting the schematic, you might blow a fuse you didn't know existed. But worse, the schematic highlights that (a TVS diode) is designed to short to ground if voltage spikes above 22V.
Engineering forums and board-level repair technicians frequently cite specific failure patterns regarding the LA-C781P. Probable Cause Diagnostic Step Corrupted BIOS or failed EC. Check for +3.3V on the BIOS chip (Pin 8). Re-flash EC_BIOS . Dead (No LED at Jack) Shorted input MOSFET or blown fuse. Measure resistance to ground on the main rail. Instant High Fan Speed Thermal sensor mismatch or failed FCH. La-c781p Schematic
: Often features the NPCE388N or similar multi-controller. Troubleshooting Common Power Issues The schematic cleverly shows a "Back Drive Protection"
When you open the LA-C781P PDF, focus on these critical pages: Re-flash EC_BIOS
(Charging IC). Pin 20 should have 19V, and Pin 6 (ACDET) should be around 2.4V to 3.1V to enable the entry MOSFETs. No 3.3V/5V Standby: