I. Description of the phenomenon, problem
The fault on the maintenance work order for the phone does not charge, plug USB does not respond.
Second, the key process, root cause analysis
1. As the motherboard for the market repair, dismantling the motherboard before doing any maintenance actions, first consider whether the motherboard is burned out or customer plug and play Damaged USB interface phenomenon, that is, the first visual inspection of J1602 (USB interface) and the surrounding components appearance, found no abnormalities.
Considering that the phone does not have any response when plugged into the USB, the motherboard fault for not charging, do not identify the USB, it is likely that USB The interface has open pins or path open phenomenon. But the measurement of the USB interface of the various pins to ground impedance, and normal board comparison are normal.
3. Since the ground impedance is normal, the motherboard is no problem with the channel, but does not mean that the motherboard voltage and power supply are normal, so view the circuit diagram , through the circuit diagram USB interface pin by pin towards the measurement of each pin path voltage.
Huawei P8 Youth Edition Mobile 4G does not charge, does not identify USB repair Figure 1
4. The measurement process and corresponding measurement points are shown in the following table.
Huawei P8 Youth Edition Mobile 4G does not charge, does not recognize USB repair Figure 2
Visible measured voltage values are also normal, but considering the VBUS_USB to charge management chip (U201) between the Also through a field effect tube Q1602, this field effect tube is to control the VBUS_USB voltage to protect U201 So we measured the voltage of VCHG (C1622) and found that the voltage is 4.23V, which can be seen after Q1602. The voltage is reduced by 0.7V. Consider the voltage reduction of the control due to Q1602 body damage.
Conclusion, solution and effect
After replacing Q1602, the phone charges normally and identifies USB normally.
IV. Summary of experience, preventive measures and standard recommendations
The two faults of not charging and not recognizing the USB are often both present at the same time, and when fixing such faults be sure to link them together for a comprehensive repair. Location. The key point of such failure is about the USB pin measurement, step by step in accordance with the pin measurement anomaly, against the wiring diagram for Find out why.