Lac781p Schematic Top Jun 2026

The IC stabilizes and biases the isolation gates, populating the primary B+ rail across the board.

Depending on the specific board configuration, it will feature Intel HD Integrated Graphics or an optional AMD Radeon Discrete GPU connected via PCIe lines.

The voltage passes through two N-channel isolation MOSFETs managed by the charging IC (often a BQ-series chip). If these MOSFETs fail or short to ground, the board will remain completely dead. Always-On Regulators (3V/5V Standby)

Intel Broadwell/Skylake U-Processor (Dual-Core, 15W TDP). Handles PCIe lanes, direct memory interfacing, SATA link, and low-power state management. lac781p schematic top

When using the schematic to diagnose "No Power" issues, focus on these top-layer sections: Check for 19V at the drain of the first N-channel MOSFET.

If 3.3V is present at the power button but the board doesn't react (no current draw change), the Super IO may not be sending the "S5_ON" or "RSMRST#" signals to wake the chipset.

Linear regulator output, usually providing 6V . The IC stabilizes and biases the isolation gates,

This indicates a complete lack of power, likely in the adapter input or primary power stages.

From the schematic top, note that the Darlington pass transistor introduces a saturation voltage of ~2V. This means your input must be at least 2V above the desired output (e.g., for 5V out, input >7V). This is higher than modern LDOs but typical for classic 78xx designs.

in more detail (which voltage comes first). If these MOSFETs fail or short to ground,

Which on the LA-C781P board are you currently inspecting? Share public link

Verify voltages at various coils; for example, 0.9V is typical for RAM and 1.1V/1.05V for chipset/PCH logic.

LAC781P (TO-220) ____________________ | (Tab connected to Pin 2 - GND) | | | | | 1 2 3 |__|__|__| | | | VIN GND VOUT