Maintenance of Apple MacBook Pro A2485 Notebook Screen with Dark Screen

Machine model: apple MacBook Pro A2485

Main board version number: 820-02100-11

Fault symptom:water damage notebook screen is dark.

Maintenance process:
Received a 2021 latest M1 MacBook Pro A2485 notebook computer,water damage caused a dark boot screen, and the external monitor could be used normally.
Machine detection, boot keyboard case can be switched, external can also be displayed.

Apple MacBook Pro A2485 notebook screen dark screen maintenance Figure 1.
Disassemble the back cover, there is still water left on it, and there is no obvious corrode.

Apple MacBook Pro A2485 notebook screen dark screen maintenance Figure 2.
Remove the motherboard.corrode on the back of the motherboard is serious.

Apple MacBook Pro A2485 notebook screen dark screen maintenance Figure 3.

Apple MacBook Pro A2485 notebook screen dark screen maintenance Figure 4.

Without drawings, the following points can be drawn from the analysis:

There is a high possibility that the position of corrode is the backlight part.
The machine can be started, the sound is normal, and all functions are very good, so the IC of corrode has nothing to do with the sound card,Nand, etc.
Look carefully next to the IC, the components without boosting backlight system, the nearest IC,Capacitor CN7, and the standard common point Capacitor.

Apple MacBook Pro A2485 notebook screen dark screen maintenance Figure 5.

After the serious treatment of corrode, the two resistors are gone.
Through the motherboard circuit, it is found that one end of the two resistors is connected with the common point of the motherboard, and the other end is connected with pin inside the IC. The impedance of this resistor is conventionally designed, and diode value should be very small, 0 ohms or 10 ohms.

Apple MacBook Pro A2485 notebook screen dark screen maintenance Figure 6.
According to the drawings, it is found that these two resistors are 0 ohm precision sampling resistors, so they should be replaced.