Discrete AMD R17M GPU with dedicated DDR3L VRAM.
Managed by a multi-phase CPU PWM controller, these rails deliver high current and low voltage (ranging from 0.8V to 1.2V dynamically) to the CPU cores and integrated graphics engine. They only turn on at the very end of the power sequence. Common Failure Points on the LA-E791P Motherboard
3. Run and Suspend Rails ( +1.2V_MEM , +1.0V_PCH , +1.05V_VCCST )
The schematic provides a detailed map of the hardware components and their electrical connections: La-e791p Rev 2.0 Schematic Diagram
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If you are working on any of the above models and see the marking CSL50/CSL52 LA-E791P Rev 2.0 silk-screened on the board itself, you are in the correct guide.
: The laptop appears to power on (fans spin, LEDs light up), but the screen remains black. Common Fixes : Discrete AMD R17M GPU with dedicated DDR3L VRAM
The motherboard is a reliable, if aging, workhorse in the HP mid-range lineup. For technicians, having the correct schematic PDF and matching BoardView file is non-negotiable for diagnosis, particularly when dealing with the Intel Skylake power sequencing or the BQ25A charging circuit.
Once +B+ (the main 19.5V system power rail) is stabilized, it powers the step-down Pulse Width Modulation (PWM) controller responsible for creating the baseline standby voltages:
Look for the (IC U5000). This is the primary gatekeeper. The schematic reveals the pinout: Common Failure Points on the LA-E791P Motherboard 3
Locate the SPI Flash IC (usually an 8-pin SOIC chip near the PCH/CPU). Verify pins 8 ( VCC - 3.3V), pin 1 ( CS# ), and pin 2 ( DO ). If voltages are correct, the flash data itself is likely corrupted. You will need a hardware programmer to re-flash the chip with a verified clean dump file containing a cleared Management Engine (ME) region matching the Kaby Lake/Skylake PCH. 5. Tips for Reading the Compal LA-E791P Document
💡 Search with the exact board number and “Rev 2.0 schematic” in quotes.
Measure the voltage on the current sensing resistor (usually labeled R010 or similar near the charging area). If it reads 0V, trace back to the entry MOSFETs.
Based on real-world repair logs, here are three frequent failures unique to this revision.
Inspect the signals to ensure the power-on signal is being sent.