LG CM9750 Service Manual page 49

ELECTRICAL TROUBLESHOOTING GUIDE
USB FUNCTION
When insert USB,
IC501 pin U7, U8, A7, A8
USB_D signal OK?
YES
A
AUX FUNCTION
IC201
pin23, 24 AUX input signal
OK?
YES
IC201
pin42, 43, 44 I2S input signal
OK?
YES
IC201
pin41 ADC_DATA_IN output
signal OK?
YES
A
NO
IC312 USB Power
+5 VU OK?
NO
Check audio cable.
NO
NO
3-30
NO
YES
Check IC501.
Replace IC201.
Replace IC312.