IQOO UI backlight brightness cannot be adjusted for maintenance after screen change

Malfunction model: ViVO iQOO UI
Fault phenomenon: After the machine falls, the screen is changed. When the machine is turned on, it is found that the backlight is the brightest state no matter how the brightness is adjusted.

IQOO UI backlight brightness cannot be adjusted for maintenance after screen change Figure 1.

Fault analysis: this backlight is in the brightest state and cannot be adjusted, mostly because the circuit is damaged, and the lamp control ic VREF cannot be given, so the CPU outputs with the rated VCC backlight.
Maintenance process: First, observe that the motherboard has not been damaged.

IQOO UI backlight brightness cannot be adjusted for maintenance after screen change Figure 2.

IQOO UI backlight brightness cannot be adjusted for maintenance after screen change Figure 3.

Find the light control here, refer to the drawings, and find that this iQOO UI version is not the same model as iQOO U1.

IQOO UI backlight brightness cannot be adjusted for maintenance after screen change Figure 4.

But its lamp control is the same one, so find the lamp control circuit and the corresponding pin bit.

IQOO UI backlight brightness cannot be adjusted for maintenance after screen change Figure 5.

I found that a resistor was burned here, and I don’t know whether it was discharged. My colleague described short-circuit here, and the backlight can be lit, but the backlight brightness cannot be adjusted.

IQOO UI backlight brightness cannot be adjusted for maintenance after screen change Figure 6.

Therefore, it is judged that either the above reference resistor is damaged here, or the original output here has been repaired, but the peer described that the machine fell and did not lose any components. The small Capacitor resistor can’t be dropped. Since short-circuit can be lit here, it is assumed that there is a pull-down reference resistor here. According to the pull-down reference resistor of Huawei backlight circuit.

IQOO UI backlight brightness cannot be adjusted for maintenance after screen change Figure 7.

Need a resistor within 10 ohm to make up, so find a Huawei machine, measure both ends of the resistor on the whole board, and find a 6.1 ohm resistor to make up.