HP Pavilion 15 (hp 15bw504ax) no display repair - LA-E841P main board

In this repair case, a customer brought an HP Pavilion 15 laptop that was completely dead with no power indication. The laptop did not respond when the power button was pressed, and there were no charging or status LEDs.

After opening the laptop and removing the bottom cover, I began troubleshooting by checking the main power input connector on the motherboard.

When the power adapter was connected, the adapter initially supplied 19V, but the voltage immediately dropped to 0V. This behavior typically indicates that the main 19V rail is shorted on the motherboard. When such a short circuit exists, the adapter’s protection mechanism shuts down the output to prevent damage.

Diagnosing the Short Circuit

To locate the source of the short, I performed a standard motherboard diagnostic procedure by measuring the resistance between ground and the main power inductors.

During this test, one of the inductors showed a direct short to ground. Further investigation revealed that this inductor belongs to the power rail supplying the graphics processor (GPU).

This finding indicated that the graphics chip power rail was shorted, which is a common failure in laptops that use dedicated GPUs.

The diagnostic process confirmed that the laptop’s 19V rail was collapsing due to a short circuit in the graphics power supply line. In many cases, this condition is caused by a faulty GPU or a shorted capacitor in the GPU power circuit.

To confirm the source of the short circuit, I removed the power inductor PLV1, which supplies power to the graphics section of the motherboard. After removing this inductor, the short circuit disappeared and the 19V main supply rail stabilized, confirming that the fault existed on the downstream side of the GPU power circuit.

Although the input supply was now stable, the motherboard still did not power on. This indicated that additional components in the graphics power stage could be damaged.

The next step was to examine the MOSFETs controlling the GPU power rail, identified as PQV1 and PQV2 in the motherboard schematic.

After measuring these components with a multimeter, PQV2 appeared to be functioning normally with no abnormal resistance readings.

PQV1, however, showed a short circuit between the drain and source terminals, which is a clear indication of MOSFET failure.

A shorted MOSFET in a switching regulator stage can prevent the power rail from operating correctly and may also cause the upstream power rail to collapse.

To proceed with the repair, I attempted to remove the faulty MOSFET PQV1 using a hot air rework station. However, the removal process was unsuccessful. Because MOSFET drain pad was welded to the copper layer due to the heat during laptop operation. therefore i had to cut down the copper layer to remove the shorted MOSFET.

After referring the schematic of the board, i realized that converting discrete graphics (dis) to UMA may solve the problem and bring board back to life.

How to convert dis to UMA

1. Disconnect power to the graphics chip. Remove PJV1 connection.

 

2. Remove Graphics power driver.

 

3. Shift R65 resistor(10k) into R67 as described in the schematic diagram.

  

4. Connect 56k into R214.

  

5. Connect pull up resistor(10k) here. some board versions does not come with this resistor.

 

After doing all those modifications, i was not lucky. when i pressed the power button, fan spins at full speed and no sign of life. therefore i removed defective graphic chip and its RAM.

  

Success !!!!. I was able to boot up the motherboard. Display was ok. I edited the bios settings and boot order. tried to install windows 10. Setup was smooth in the beginning. But somewhere middle of the installation, machine freezed with the following screen.

 

This issue occurs because the BIOS is configured to recognize a discrete graphics subsystem. Internally, it retains a mapped address space intended for switching and communicating with dedicated GPU hardware. However, since the discrete graphics hardware is no longer physically present, the operating system still attempts to access this predefined address during initialization or driver loading. As a result, the system becomes unresponsive, as there is no actual hardware available to respond to these communication requests.

The solution to this issue is to program the BIOS with firmware that supports only UMA (Unified Memory Architecture) graphics. To achieve this, the BIOS was reprogrammed using firmware from the HP Pavilion 15-BW255G6 motherboard, which is designed to operate exclusively with integrated (UMA) graphics. This approach eliminates references to discrete graphics hardware, and the system operated successfully after the modification.