U disk failure and maintenance

When the following faults are repaired, first of all, USB interface damage and PCB board welding should be eliminated, and the USB extension cable is normal, and then maintenance judgment.
1. There is no reaction when the USB flash drive is inserted into the machine
Maintenance ideas: According to the fault phenomenon, the whole U disk does not work, and the conditions that U disk tools must have are the focus of our maintenance. No matter what the U disk of any scheme wants to work, it must have the following conditions:
(1) power supply, 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, there are three pins are power input (5V), ground, power output (3.3), The working principle is that when the input pin inputs a 5V voltage, the output pin will output a stable 3.3V. As long as you find out where the root cause of the lack of power supply is, the problem will be easily solved.
(2) Clock, because the master must work at a certain frequency, and FLASH communication must also be transmitted with the clock signal, so if the clock signal is not, 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 is damaged. Just change the control.
2. When the USB flash drive is inserted into the computer, the message "Unrecognized device" is displayed.
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 in checking this circuit as long as the measurement between the data line and the main control line is normal, generally between the data line and the main control circuit will be connected to 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 points are normal, it can be judged that the main control is damaged.
3, you can recognize the U disk, but when you open the prompt "disk has not been formatted" but the system can not format, or prompt "Please insert the disk", open the U disk inside is garbled, the capacity is not consistent with itself, etc.
Maintenance ideas: For this phenomenon, you can judge that the hardware of the U disk itself is not much of a problem, but a software problem.
Solution: Find the master control solution repair tool to get it. This requires everyone to see what the main control of the U disk is to decide.
FLASH disk failure The failure to write or store files is generally caused by poor flash performance or bad blocks. U disk is different from MP3, there is no firmware, but some manufacturers put their own software inside, there will be no low grid.
Tell you a very simple way, that is, when the main control is damaged or can not find the corresponding repair tools, you can use the USB FLASH kit to re-make a new USB flash disk, the method is to remove the flash of the faulty machine and put it on the new PCB board. U disk kit includes (PCB with master control (1.1/2.0) and a set of shell), maintenance is very simple, and data recovery is more convenient.