LG SNC4R Service Manual page 46

ELECTRICAL TROUBLESHOOTING GUIDE
ADAPTER POWER CIRCUIT
USB_5V is not 5 V
Check F301 Voltage 25 VA
Check FB304 Voltage 12 VA
Check FB305 Voltage 5.1 VA
Check FB306 Voltage 5 V
OK
YES
YES
YES
YES
YES
NO
NO
NO
NO
3-17
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Check Adapter
Replace Main PCB
Replace Main PCB
Replace Main PCB
Only for training and service purposes.