water damage Apple MacBook Pro A2338 Computer Screen Dark repair

Machine model: Apple MacBook Pro A2338

Main board model: 820-02020-A

Fault: The computer screen is dark.

Maintenance process:

I received an Apple MacBook Pro A2338(M1), and the customer described that the notebook water damage had been cleaned, but it still didn’t work.

Remove the back cover, plug in the charger, the current has been turned on, use the lower case key to turn on the light, use the flashlight to illuminate the screen, and find that the computer screen is dark.

Disconnect the power-off screen interface, and visually inspect it. It is found that there is no trace of water damage corrode on the interface.

Before, there was a notebook with a broken shell and cracked liquid crystal. You can see the upper half of the light. After installing the test, it was found that the backlight was still not bright, which was caused by the motherboard.

Remove the motherboard, and visually check that the motherboard is relatively clean. Measure the key points of the main board, starting with the display interface JP600. Because of the dark screen of the machine, the LPDP display data part and MIPI_FTCAM Camera data part can be skipped directly for the time being, and no measurement is needed.

water damage Apple MacBook Pro A2338 Computer Screen Dark repair figure 1.

Focus on checking the boosting part:

1.PPVOUT_LCDBKLT

2.PP3V3_SW_LCD_CONN

water damage Apple MacBook Pro A2338 Computer Screen Dark repair figure 2.

PP5V_SW_LCD_CONN

water damage Apple MacBook Pro A2338 Computer Screen Dark repair figure 3.

4.I2C_BKLT_SCL，I2C_BKLT_SDA

water damage Apple MacBook Pro A2338 Computer Screen Dark repair figure 4.

For the key points of the boosting part, the ground impedance tests PPVOUT_LCDBKLT, PP3V3_SW_LCD_CONN, PP5V_SW_LCD_CONN, I2C_BKLT_SCL and I2C_BKLT_SDA are normal, and no abnormality is found.

Turn on the key points of the step-up part, and connect it to the screen for testing. PPVOUT_LCDBKLT VCC is normal, PP3V3_SW_LCD_CONN 3.3v is normal, and only 1.8V of PP5V_SW_LCD_CONN VCC is abnormal. I2C_BKLT_SCL,I2C_BKLT_SDA, temporarily unable to measure with VCC.

Determine the fault point, PPVOUT_LCDBKLT, without VCC; PP5V_SW_LCD_CONN, only 1.8v; 3. According to the backlight power-on sequence, first check the screen, I2C bus communication is normal, turn on the screen 3v,5v screen VCC, and boost the voltage.

The probability that the screen VCC of PP5V_SW_LCD_CONN is only 1.8v is relatively high, so it should be traced and repaired first. Open the drawing, inquire from the source and pass PR621, the test resistance is normal, and the other end is only 1.8v

water damage Apple MacBook Pro A2338 Computer Screen Dark repair figure 5.

water damage Apple MacBook Pro A2338 Computer Screen Dark repair figure 6.

Continue to trace the source of PP5V_SW_LCD from UP700, inquire about its working conditions and find that the problem is VCC convert transistor, and the test main V VCC is only 1.8v, so the DS conduction is only 1.8V. It is determined that the problem is that PP5V_S2 VCC is low, only 1.8V, and the ground impedance is normal.

water damage Apple MacBook Pro A2338 Computer Screen Dark repair figure 7.

Tracing the source of PP5V_S2, UC300 measured the working conditions of the VCC IC, the main VCC and VCC were normal, and some problems of BST bootstrap boost were found. RC332 CC332 had corrode, and the measured resistance was more than 500 ohms. After replacement, the startup was normal.