The mobile phone can't adjust the backlight brightness after changing the screen of VIVO iQOO UI

The mobile phone can’t adjust the backlight brightness after changing the screen of VIVO iQOO UI.

After changing the screen of VIVO iQOO UI, the mobile phone can’t adjust the brightness of the backlight. This backlight is the brightest state and cannot be adjusted. Most of the circuits are damaged, so it can’t give the reference voltage to the light control IC. Therefore, the CPU outputs with the rated voltage of the backlight.

Machine model: VIVO iQOO UI version

Symptom: The backlight brightness cannot be adjusted.

Maintenance process:

A second-repaired VIVO iQOO UI, fault description: The screen was changed after the machine fell. When it was turned on, it was found that the backlight brightness could not be adjusted, and the backlight was in the brightest state.

Mobile phone cannot adjust backlight brightness after screen change of VIVO iQOO UI Maintenance Figure 1

This kind of backlight can’t be adjusted in the brightest state, mostly because the circuit is damaged, and it can’t give the reference voltage to the lamp control IC, so the CPU outputs with the rated voltage of the backlight. First, observe the motherboard.

Mobile phone cannot adjust backlight brightness after screen change of VIVO iQOO UI Maintenance Figure 2

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

Mobile phone cannot adjust backlight brightness after screen change of VIVO iQOO UI Maintenance Figure 3

But its light control is the same one. Find the light control circuit and find the corresponding foot position.

Mobile phone cannot adjust backlight brightness after screen change of VIVO iQOO UI Maintenance Figure 4

I found a resistor burned here. I wonder if it is discharged. The home is directly shorted here, and the backlight can be lit, but the brightness of the backlight cannot be adjusted.

Mobile phone cannot adjust backlight brightness after screen change of VIVO iQOO UI Maintenance Figure 5

It is judged that either the reference resistor above is damaged or the original one has been repaired.

Since the short circuit can be lit, it is assumed that there is a pull-down reference resistor here. According to the pull-down reference resistor of Huawei backlight circuit.