Schematic: La-c781p

: DDR3L (1.35V) or DDR4 (depending on the specific revision generation)

When the power button is pressed, the EC sends enable signals to turn on the remaining rails: Powers the DDR3L memory modules.

Power enters through the DC jack, passes through an EMI filter, and reaches the first two isolation MOSFETs (often labeled PQ42 and PQ44, or similar depending on the exact revision). La-c781p Schematic

This section details the complex power distribution system on the LA-C781P. It includes the DC-in jack, the charging circuit for the battery, and various voltage regulators that convert the main power source into the different voltages required by the CPU, RAM, and other components (e.g., 3.3V, 5V, 1.05V, etc.). Troubleshooting power-on issues often begins here.

If you are currently troubleshooting a specific issue on this motherboard, let me know (e.g., completely dead, fan spins but no display, blinking LED error codes), what power rails you have already measured , and if you have access to a DC regulated power supply . I can guide you to the exact components or pins to check next. Share public link : DDR3L (1

A common point of failure where the KBC (keyboard controller) shorts out, preventing the charging light from illuminating.

The Compal LA-C781P motherboard represents a common architecture in budget notebooks. While finding the official PDFs requires searching specific forums, the resources are out there and are essential for professional repair. It includes the DC-in jack, the charging circuit

: Verify 19V input at the DC jack. In many failure cases, 19V is present at the first N-channel MOSFET drain but fails to pass through to the source because of a missing gate signal from the charging IC. Charging IC (bq25a) Pins : Pin 20 (VCC) : Should have ~19V.

If the laptop shows no signs of life (no LEDs, no fan spin), technicians must first locate the inductors (coils) for these two rails to verify if 3.3V and 5V are present immediately after plugging in the AC adapter. Secondary and Run Rails ( +1.0V_RUN , +1.35V_RAM , +VCC_CORE )