Figure 3.3.2.2 Troubleshooting diagram for “USB is not
2. Troubleshooting flow chart for “USB is not connected” is shown in the picture 3.3.2.2:
Y
Y
Y
Y
Y
N
N
N
N
USB is not connected
Check whether 5V
of Q2 is grounded
normally
Check whether 3.3V
and 1.8V are normal
Check
D+, D- resistance
to ground
Upgrade software
Q2 has trouble or USB
socket has rosin joint
Check each DC-DC switch
circuit and peripheral elements
Check whether T1 or USB
socket has rosin joint
Check
whether oscillation
of 12M crystal oscillator
is normal
Change crystal oscillator
or capacitor n two sides
Change the main decode
chip
Whether
software upgrading is
available
N
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