Usb Troubleshooting - LG U970 Service Manual

4. BB Trouble Shooting

4.11 USB Troubleshooting

USB Initial sequence of U970/KU970 is :
USB connected to U970/KU970 power on → USB_VBUS(Q400) go to 5V → USB_D+ go to 3.3V →
48M Crystal on → USB_DAT is triggered → USB work.
Power is on?
Cable is inserted?
Q400 pin 4 is 5V?
USB_D+ is 3.3V?
48M clock is running?
Change the Main board
Start
NO
YES
NO
YES
NO
YES
NO
YES
NO
YES
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4. TROUBLE SHOOTING
Go to power on trouble shooting
Insert cable
Check Q400 (pin 4)
Check U503 (pin 6)
Check X200