LG CM9750 Service Manual page 40

NO SOUND
There is no sound output in the PORT. IN function, repair the set according to the following guide.
10-3. PORT. IN FUNCTION
10-3-1. Solution
Replace IC201 on MAIN board.
10-3-2. How to troubleshoot (Countermeasure)
1) Check PT_L/R signal from FRONT board to MAIN board.
2) Check if PT_LR is entered pin25 & 27 of CN605  pin25 & 27 of CN315.
3) Check PT_L/R signals to IC201(pin9, 10).
4) Check if ADC_BCK, ADC_LRCK & DAC_MCLK are entered from IC501 to IC201.
5) Check if ADC_DATA is entered from IC201 to IC501.
  If no signal, check +5 V & +3.3 V(ADC) for IC201. If is NG, replace it a new one.
6) Check the following I2S signal flow from IC501 to IC202.
  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.
7) Check if the digital audio AMP block is okay.
  If AMP is damaged, replace it with a new one.
10-3-3. Service hint (Any picture / Remark)
POT_L/R
IC201
VOLUME
CS5346
ADC/MIC_DATA
MCS_MCLK
MCS_BCK
IC501
MCS_LRCK
MLC3730
MIX_DATA_OUT
< PORT. IN function signal fl ow >
ONE POINT REPAIR GUIDE
POT. IN
Board
IC202
IR AMP
PS9860
IRS2092+IRF6775
PWM
< MAIN board bottom view >
3-21
IC201 IC201
PT_L/R PT_L/R