Usb Trouble - LG U990 Service Manual

4.7.1 USB trouble

USB Initial sequence of KU990 is :
USB connected to KU990 → USB_VBUS(C540) go to 5V
→ USB_D+(VA202) go to 3.3V → 48M Crystal on → USB_DATA is triggered → USB work
Cable is insert?
USB_VBUS is about
USB_D+ is about to 3.3V?
Change the Main board
U507(USB_D+)
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Start
NO
YES
NO
to 5V?
YES
NO
YES
NO
48MHz is run?
YES
VA500(USB_D+)
X200(48MHz)
R514(USB_VBUS)
C540(USB_VBUS)
U500(USB_VBUS)
U304(USB_D+)
4. TROUBLE SHOOTING
Cable insert
Check C540, R514,U500
USB cable
Check VA500,U507,U304
Check X200
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