Prompt for "unrecognized device" after inserting U disk

1.U Disk Interface Circuit

U disk Interface circuit only two data line d+, D-, in the inspection of this circuit, as long as the data line to the main control chip between the test can be. Between the data line and the main control circuit has a string of two small resistance resistors, this resistance is to protect the resistance, so the resistance of the two resistors to check whether normal.

2. Clock circuit

u disk and computer communication, to be in the same frequency, if there is no synchronization, the system will be considered an "unrecognized device", then the crystal vibration will be replaced.

If the above two points are normal, it may be the main chip damage.