LG CM9730 - No Sound

3-17
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output in the USB FUNCTION, repair the set according to the fol-
lowing guide.
6-2. IN THE USB FUNCTION
6-2-1. Solution
Please check and replace IC501, IC504 on MAIN board & IC3U01 on USB board.
6-2-2. How to troubleshoot (Countermeasure)
1) Check +5VU to USB board.
 If +5.6 VA to pin2 of IC3U01(LDO) doesn’t come out, check pin4, 5 of CN502.
 If +5.6 VA is normal & +5VU of IC3U01 pin3 doesn’t come out, then replace IC3U01.
2) Check USB D± from main board to USB board.
a. Check USB_HUB_DN/DP signals to IC501(pin16, 18)
b. Check USB1/2_DN/DP signals from IC501 to CN502 (pin1, 2, 9 & 10)
 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”.
6-2-3. Service hint (Any picture / Remark)
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IR AMP
IRS2092+IRF6775
USB
Board
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IC504
USB2512B
USB1_D+/-
USB2_D+/-
USB_D+/-
< Waveform of USB D± signal >
USB D+ / D- (CN502 Pin1, 2 & 9, 10)
< USB function signal fl ow >