La-c781p — Schematic ~upd~

Based on technician repair guides, here are the critical stages for diagnosing a "Dead" LA-C781P board: 1. VIN Section & Input MOSFETs

The entry point of the 19V DC-in often features two N-channel MOSFETs. If these are shorted, the board will be completely dead with no lights. The schematic helps identify the "gate" signals coming from the charging IC to see if they are being driven correctly. C. Corrupted BIOS/EC Firmware

Let’s walk through a real-world example: Dell Precision 7510, no power, no fan spin. La-c781p Schematic

These can short to ground, preventing the 19.5V from reaching the rest of the board.

| Page Range | Block/Function | Description | |------------|----------------|-------------| | 1-3 | Block Diagram & Power Tree | High-level power flow (e.g., DC_IN → +PWR_SRC → +3.3V_ALW) | | 4-10 | CPU & PCH Core | VCC_CORE, VCCGT (Graphics), VCCIO, VCCSA | | 11-20 | System Memory (DDR4) | SODIMM slots A/B, data lines, SPD, VDDQ | | 21-30 | PCH & I/O Interfaces | SATA, USB 3.0, PCIe, LPC bus, SPI (BIOS), HDA audio | | 31-40 | Embedded Controller (EC) | ITE IT8587E, keyboard, fan control, power sequencing | | 41-50 | Power Management ICs (PMIC) | Charger (BQ24780S), DC-DC converters (SY8288, TPS51285) | | 51-60 | Discrete GPU (NVIDIA) | Quadro power phases, FBVDDQ, VDD_GFX_CORE | Based on technician repair guides, here are the

💡 If the charging IC is faulty and a replacement isn't available, some technicians use a DC power supply to manually "tap" the MOSFET gates for testing, though this prevents battery charging.

Repair technicians often encounter "No Power" or "No Start" conditions with this board. Common diagnostic steps include: The schematic helps identify the "gate" signals coming

Measure the gate pins of the input MOSFETs. It must read higher than 19V (usually ~24V) to turn on N-channel switches. If it reads 0V, use the schematic to verify the VCC , ACIN , and REGN supply pins of the charging IC.