LG U990 Service Manual page 115

4. TROUBLE SHOOTING
4.7.2 UMS(USB MASS STORAGE) trouble
UMS Initial sequence of KU990 is :
USB connected to KU990 → VREG_5V(R335, UMS) go to 5V → VREG_USB_3.3V(R301) go to 3.3V
→ USB_DATA is triggered → USB work
MICRO SD function OK?
Change the Main board
D501(VREG_5V)
LGE Internal Use Only
Start
Cable is insert?
YES
VREG_5V is about
to 5V?
YES
VREG_USB_3.3V is
about to 3.3V?
YES
YES
C529 (VREG_USB_3.3V)
NO
Cable insert
NO
Check R335, D501
NO
Check R301,C529, USB CABLE
NO
Follow the micro sd trouble
< TOP SIDE >
R301(VREG_USB_3.3V)
Copyright © 2007 LG Electronics. Inc. All right reserved.
- 116 -
R335(VREG_5V)
Only for training and service purposes