LG OK75 - Troubleshooting: No Sound (USB Function)

3-16
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Only for training and service purposes.
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output in the USB Function, repair the set according to the following guide.
6-3. USB FUNCTION
6-3-1. Solution
Replace IC204 on MAIN board.
6-3-2. How to troubleshoot (Countermeasure)
1) Check +5V_USB to USB board.
 If the USB LED are turned on, the voltage is okay, if so not, check USB_5V to pin4, 5 of CN803.
2) Check USB D1± or USB D2± from MAIN board to TOP board.
a. Check 2.0_D1±signals(pin U7, U8 ) or 1.1_D1± signals(pin A7, A8 ) to IC501.
b. Check USB± signals to CN502(pin1, 2, 7, 8).
 If there is any trouble, check the power for IC207.
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 6-1 is normal.
6-3-3. Service hint (Any picture/ Remark)
USB D-/D+ (CN502 pin1, 2 & pin7, 8)
< Waveform of USB D± signal >
D
D+
D-
< MAIN board top view >
CN502
CN502
IC501
IC501