LG CM4520 Service Manual page 32

NO SOUND
There is no sound output in the USB FUNCTION, repair the set according to the fol-
lowing guide.
5-3. IN THE USB FUNCTION
5-3-1. Solution
Please check and replace IC801 on MAIN board & IC502 on USB board.
5-3-2. How to troubleshoot (Countermeasure)
1) Check +5VU to USB board.
If the USB LED are turned on, the voltage is okay, if so not, check +5.6 V to pin6 of CN502.
2) Check USB D± from MAIN board to USB board.
a. Check USB_DN/DP signals to IC801(pin116, 117).
b. Check USB± signals to CN502 (pin1, 2, 4, 5).
If there is any trouble, check the power for each IC. The power is normal but , if the signal waveform to
the IC is distorted or no signal, replace it with a new one.
3) Check if "Digital audio AMP block" on item 5-2 is normal.
5-3-3. Service hint (Any picture / Remark)
USB
HUB IC
DAC_DATA
DAC_LRCK
IC801
MLC9800
DAC_BCK
DAC_MCLK
< USB function signal fl ow >
ONE POINT REPAIR GUIDE
USB
IC601
AMP IC
PS9854
TAS5612L
PWM
3-13
< Waveform of USB D± signal >