How to repair U disk chip common failure

Nothing happened when the USB flash drive was plugged into the machine
Maintenance ideas: According to the fault phenomenon, the U disk machine does not work, we can find the cause of the fault through some methods and solve
1. Power Supply
U disk chip power supply is divided into the power supply required by the main control and the power supply required by FLASH, these two are the key, and the U disk circuit is very simple, such as no power supply is generally insurance inductance damage or 3.3V regulator block damage, when it comes to the regulator block again here also say, The three pins are power input (5V), ground, and power output (3.3). The working principle is that when the input foot inputs a 5 voltage, the output foot will output a stable 3.3V. As long as you find out where the source of the power supply is, the problem will be solved well
2. Clock
Because the master must work at a certain frequency, and the FLASH communication also needs the clock signal to transmit, so if the clock signal is not available, the master must not work. When checking this aspect of the circuit, in fact, the clock generation circuit is very simple, only need to check the crystal oscillator and its peripheral circuit can be, because the crystal oscillator is afraid of brushing and the U disk is small and easy to fall on the ground caused by the crystal oscillator damage, as long as the same crystal oscillator can be replaced. Note: Crystal vibration is not measurable, the best way to judge its quality is to replace a good crystal vibration to judge.
3. Main control
If the above two conditions are normal, that is the main control chip of the u disk is damaged. Just change the control
The computer prompts "Unrecognized device"
Maintenance ideas: For this phenomenon, the first point shows that the circuit of the U disk is basically normal, but there is a fault in communication with the computer, and for communication there are the following points to check:
1, U disk interface circuit
There is no special component in this circuit is two data lines D+D-, so when checking this circuit as long as the measurement between the data line and the main control line is normal, it is generally connected between the data line and the main control circuit will be two small resistance values, in order to play a protective role, so to check whether the resistance value of the two resistances is normal.
2. Clock circuit
Because the USB flash drive and the computer to communicate at a certain frequency, if the working frequency of the USB flash drive and the computer can not be synchronized, then the system will think that this is an "unidentifiable device". It's time to change the crystal oscillator. There are many instances of crystal vibration damage in actual maintenance!
3. Main control
If the above two checks are normal, it can be judged that the main control is damaged