1. Check whether the welding between the Micro USB port and the mainboard is normal;
2. Confirm whether the 3.8V power supply is normal;
3. Supply power with DC Digital power, press the Power on key and Volume increase key to enter the loading firmware mode at the same time for about 3 seconds, then release it. And observe whether the current is maintained at about 30mA; If the current is normal (the module has entered the loading firmware mode), check whether the USB switch U4 and its periphery circuit are normal. If the current is abnormal (the module has not entered the loading firmware mode), check whether the Q11, Q12, Q and 24 triodes are normal or not. And check whether the key circuit is normal.