These voltages are critical for powering the Super I/O chip and the SPI BIOS chip before the user ever presses the power button. 3. S5 to S0 State Transition Upon pressing the power button: The Super I/O sends an enable signal to the PWM controller.
The main power rail (VIN). It enters through the DC jack and passes through two entry MOSFETs controlled by the charging IC. +3VALW / +5VALW: "Always-on" rails. On this board, the RT8243 (PU2) often acts as the PWM controller for these voltages.
+3VALW powers the Embedded Controller (KB9022Q) and the BIOS ROM chip. +5VALW powers USB ports and sleep-state circuits. Suspend and Run Rails (S3/S0 State)
Utilizes Intel HD Integrated Graphics, with some premium configurations featuring an optional AMD or NVIDIA discrete GPU (dGPU) embedded on the PCB.
The is a vital blueprint for electronics engineers and component-level repair technicians. This specific motherboard layout—often designated as ABL51—is commonly used in Lenovo Ideapad laptops (such as the Ideapad 300 series). La-c781p Schematic
Two DDR3L (1.35V) SO-DIMM slots supporting up to 16GB of RAM.
This guide provides a comprehensive overview of the LA-C781P motherboard, how to use its schematic for repair, common faults, and where to find the essential files and BIOS binaries you need to bring a dead laptop back to life.
This chart tells you the order in which voltages must turn on. If +3VALW is missing, +5VALW will never start.
A schematic diagram is a visual representation of an electronic circuit, showing the components, their connections, and relationships between them. It serves as a blueprint for engineers, technicians, and manufacturers to understand, design, and build electronic devices. Schematics are essential in the development, testing, and repair of electronic equipment. These voltages are critical for powering the Super
Single or dual-channel DDR3L (low voltage 1.35V) SO-DIMM slots. ⚡ Power Distribution & Sequence
Dedicated pages for the 3.3V/5V "Always-On" buck converters. 5. Troubleshooting Steps
What is the laptop showing? (e.g., completely dead, blinking light codes, spinning fan but no display?)
Compal LA-C781P (ABL51) is a laptop motherboard commonly found in the The main power rail (VIN)
Ensure 19V is present after the entry MOSFETs.
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If pin 4 has 0V, the 19V rail will not pass the second MOSFET, leaving the board with no power. 2. Charging IC Requirements (BQ25A) To function correctly, the IC requires: Pin 20 (VCC): ~19V power supply. Pin 6 (ACDET): Usually ~2.4V to 2.8V to detect the adapter. Pin 16 (REGN): Should output a stable 6V . 3. Power-On Sequence