Usb Trouble - LG U300 Service Manual

4.9. USB Trouble

USB Initial sequence of U300 is :
USB connected to U300 → USB_VBUS(U403 Pin_4) go to 5V → USB_D+(U403 Pin_1) go to 3.3V →
48M Crystal on → USB work.
Cable is insert?
USB_VBUS is about
USB_D+ is about to 3.3V?
Change the Main board
USB_D-
(U403 6pin)
USB_D+
(U403 1pin)
USB_VBUS
Start
NO
YES
NO
to 5V?
YES
NO
YES
NO
48M is run?
YES
- 99 -
4. TROUBLE SHOOTING
Cable insert
Check U403,USB cable
Check U403
Check X200
X200(48MHz)