(also known as the Compal ABL51 ) is a motherboard schematic frequently used in HP 15-af series
laptops. It is a common reference point for technicians troubleshooting "no power" or "no display" issues on these budget-friendly AMD-based machines. Board Specifications Model Name : Compal ABL51 LA-C781P. : Designed for AMD processors (e.g., A4-5000, A6-6310) using the BGA769 (FT3b) socket. : Supports (Low Voltage) RAM across two slots. Application : Primary motherboard for the notebook series. Troubleshooting "Top" Faults
If you are working with this schematic, these are the most reported issues encountered by repair experts: VIN Circuit Failure
: A common "dead" board symptom where the 19V main power rail enters the board but fails to distribute due to faulty MOSFETs or current sense resistors near the power jack. Missing Always-On Rails : Technicians often check for the
standby voltages. If these are missing, the laptop will not respond to the power button. BIOS/EC Corruption
: The board may appear dead or fail to trigger if the Embedded Controller (EC) or BIOS firmware is "frozen." A hard reset (pulling main and CMOS batteries) is a standard first step. Low Power Consumption
: A healthy standby board typically draws very low current (approx. 10mA). If it stays at this level after pressing the power button, it indicates a "no trigger" fault, often tied to missing power-on signals from the Super I/O chip.
The LA-C781P (also known as ABL51) is a motherboard manufactured by Compal for the HP 15-AF series laptops.
If you are looking for technical data to repair or analyze the "top" (primary component side) of this board, Board Layout & Component Overview
The LA-C781P typically supports AMD A-Series processors (such as the A8-7410 or A4-5000) and features a compact design common in budget HP notebooks. Processor: Integrated BGA CPU (e.g., AMD A8 or A4). Memory: Two DDR3L RAM slots.
Graphics: Integrated Radeon HD graphics or dedicated GPU variants like the HD 8600 2GB. Power Rail: Uses a 19V main power rail (VIN circuit).
Common Failure Points: Repairs often focus on the "VIN" circuit or missing standby voltages like #+3VALW_EC. Where to Find Schematics & Boardviews
Full schematic diagrams for Compal boards like the LA-C781P are proprietary but can be found through specialized technician databases:
Schematic Sources: Technical documents for the Compal ABL51 LA-C781P are available on platforms like Laptop-Schematics and OlderGeeks.
Repair Guides: For visual troubleshooting of the top side, sites like DIY-LaptopRepair offer guides specifically for this model.
Video Walkthroughs: Technicians often provide "top-down" repair views and circuit explanations on YouTube, specifically addressing No Power issues on this board. lac781p schematic top
The Compal LA-C781P (ABL51) is a motherboard commonly found in HP 15-af and HP 255 G4 series laptops. This guide provides a technical overview of its primary "top-side" components and common troubleshooting steps based on its schematic design. 1. Primary Components (Top View)
The "top" of the LA-C781P board typically contains the following critical systems:
Processor (APU): Most versions feature an integrated AMD A-Series (e.g., A6-6310) or E-Series APU soldered directly to the board.
Memory Slots: Supports DDR3L (1.35V) SDRAM with a maximum capacity of 8GB across two slots.
Charging IC: Typically uses the bq24725A (labeled bq25A) to manage power input and battery charging.
Embedded Controller (EC): Uses the KB9022Q chip to manage power sequencing, keyboard input, and fan control.
Storage Interface: Provides a SATA III (6 Gb/s) connector for HDDs or SSDs. 2. Common Power Rail Schematics
When troubleshooting a "No Power" issue, technicians check these specific points on the LA-C781P: Power Rail Description Test Point / Component +19V (VIN) Main adapter voltage Check DC-in Mosfets and CLR (Current Limit Resistor). +3VLP / LDO Low drop-out always-on voltage Available at the RTC cell and battery connectors. +3VALW / +5VALW Always-on system power Generated by the RT8243 (PU2) step-down IC. ACDRV Gate control for entry Mosfets Should be ~25V if the bq25A IC detects a valid adapter. 3. Troubleshooting "No Power" (Dead Board)
If the laptop does not turn on and consumes 0.00A on a DC power supply, follow this diagnostic path:
Check VIN Section: Verify 19V is reaching the first Mosfet's drain.
Verify ACDRV: If the source of the entry Mosfets has 0V, check if the bq25A charging IC is outputting ~25V on Pin 4 (ACDRV). If it is 0V, the IC may be faulty or sensing a short circuit.
LDO Check: Confirm 3.3V is present at the RTC battery connector. If missing, the 3V/5V regulator IC (RT8243) may be damaged.
Short Circuit Test: Use a multimeter in "Diode Mode" or "Beep Mode" on all major coils to ensure no power rails are shorted to ground. 4. Upgrade Compatibility
RAM: Must use DDR3L (Low Voltage). Standard 1.5V DDR3 may cause stability issues or fail to boot.
SSD: Any standard 2.5-inch SATA SSD is compatible for a significant performance boost over the original HDD. (also known as the Compal ABL51 ) is
LA-C781P Motherboard Schematic Overview Compal LA-C781P (often labeled as ) is a common motherboard found in series laptops. It features an AMD Stoney Ridge or similar APU architecture and utilizes the embedded controller. Technical Quick Specs : Compal ABL51 Common Laptop Models : HP 15-af011ur, HP 15-af series Embedded Controller (EC) : ENE KB9022Q Main PWM Controller : Often utilizes the for power rails (e.g., positive 3 cap V cap A cap L cap W cap P positive 5 cap V cap A cap L cap W cap P Troubleshooting Common Issues If you are dealing with a "No Power" (Dead) state, technicians frequently focus on the VIN circuit and the power sequence for the EC. Check the +3VALW rail : Ensure it is reaching pin 15 of the EC (KB9022Q). VIN Circuit
: Inspect the initial MOSFETs and the current sensing resistor for standard DC-in voltages. Resources for Repair Schematics & Boardview : You can find downloadable PDF schematics and boardview files on technical forums like DIY-LaptopRepair or specialized archives like Laptop-Schematics Community Guides : Detailed repair guides for specific models like the HP 15-af011ur are available on DIY-LaptopRepair
: Always verify all connections are secure and run diagnostics before and after board-level repairs. measurement or a for a particular component on this board?
Based on the alphanumeric code "LAC781P" and the request for a "schematic top," it is highly likely that you are dealing with a printed circuit board (PCB) or a specific electronic module where this designation refers to the component placement on the top side of the board.
Because "LAC781P" is not a widely recognized standard industrial part number (like a generic 7805 voltage regulator or a 555 timer), it is likely a custom OEM part number, a specific house number for a manufacturer (such as a car audio module, industrial controller, or appliance board), or a specific revision code.
Below is a technical report template regarding this designation, including how to interpret it and steps to find the specific schematic you need.
In the context of a "Top View" schematic or service sheet, you are typically looking at the component placement layer. Here is the general layout and signal flow for this type of module:
1. Input Section (Usually Top of Board):
T1 or Trafo. This provides galvanic isolation and the balanced-to-unbalanced conversion.R1 or Gain) to set the nominal input level.2. Equalizer Section (Middle of Board):
3. Output/Bussing Section (Bottom of Board):
4. Power Supply Regulation:
The keyword "lac781p schematic top" encompasses more than just a diagram—it represents the complete understanding of a reliable, classic linear regulator from its high-level circuit connections down to the physical placement on a PCB’s top layer.
By mastering the standard application circuit (input filtering, regulator, output decoupling) and recognizing that LAC781P is functionally a 7812 in TO-220 package, you can confidently repair old equipment, design new power supplies, or adapt it into larger audio or embedded projects.
Remember these key takeaways:
Whether you are a student building your first bench supply or a technician restoring legacy hardware, the LAC781P’s straightforward top-level schematic will serve you reliably for years to come. Keep a copy of this guide handy, and you’ll never be lost when you encounter that enigmatic three-terminal regulator labeled LAC781P. Schematic Top View (Component Layout) In the context
Appendix: Quick Reference – LAC781P Pinout (Top View)
LAC781P (TO-220)
____________________
| (Tab connected to Pin 2 - GND)
| | | |
| 1 2 3
|__|__|__|
| | |
VIN GND VOUT
For further reading, search for "L7812CV datasheet" and "linear power supply design tutorial."
The (ABL51) is a motherboard schematic manufactured by Compal Electronics, primarily used in HP 15-AF series laptops.
This "top-level" documentation is essential for technicians performing board-level repairs, such as fixing "no power" issues. Motherboard Specifications
Based on technical teardowns and available documentation for the Manufacturer: Compal Electronics (OEM).
Associated Laptop Model: HP 15-AF series (e.g., HP 15-af011ur, HP 15-af123ur). Processor Architecture: Typically utilizes AMD processors. Revision: Commonly referenced as Rev 1.0 or Rev 1_OLD. Critical Power Stages
The schematic outlines several vital power Rails and ICs required for the laptop to boot:
Charging IC (BQ25A): Responsible for voltage boost and controlling the N-channel MOSFET gates. If the "AC Drive" (Pin 4) does not output voltage (typically 22–23V), the motherboard will fail to power on.
Step-Down Section: Manages the conversion to 3.3V and 5V rails, which are necessary for the standby power state.
3V LDO: Found at the RTC cell and battery connectors; its presence indicates the initial power stage is functional even if core voltages are missing. Common Troubleshooting Steps Technicians use the schematic to diagnose "dead" boards by checking:
VIN Section: Verifying 19V input at the DC jack and through the first two MOSFETs.
Short-Circuit Testing: Using a multimeter in "beep mode" on all coils to identify grounded power rails.
Voltage Injection: If a specific rail (like 3.3V) is missing, low voltage may be injected to identify overheating components using thermal imaging or touch. Documentation & Resources
For full technical details, including boardview files and circuit diagrams, you can find resources through the following platforms:
The output pin is directly connected to the emitter of the pass transistor. From the schematic top, you also see a discharge path (a resistor to ground) that ensures the output voltage falls quickly when input power is removed, preventing latch-up conditions.