LG CM9750 Service Manual page 42

NO SOUND
There is no sound output in the MIC IN function, repair the set according to the following guide.
10-5. MIC IN FUNCTION
10-5-1. Solution
Replace IC200, IC206 on MAIN board.
10-5-2. How to troubleshoot (Countermeasure)
1) Check MIC_SIG signal to pin33 of CN605.
  If no signal, Check the signal to pin33 of CN315 on the FRONT board.
Check if the signal is entered from pin6 of CN605 to MAIN board.
2) Check if MIC_SIG is entered from pin33 of CN605 to pin3 to IC200 (MIC AMP).
3) Check if the amplified signal comes out from pin4 of IC200.
  If no signal output, check +12 V for IC200, replace IC200 with a new one if it has a problem.
4) Check if MCS_BCK, MCS_MLCK & MCS_LRCK is entered from IC501 to IC206.
Check if MIC_DATA_IN is entered from pin9 of IC206 to pin T1of IC501.
  If no signal, check +5 V & +3.3 V for IC206. If it is abnormal, change replace it a new one.
5) Check the following I2S signal flow from IC206 to IC501.
  If there is any trouble, check the power for each IC. If the signals are abnormal, replace it a new one.
6) Check if the digital audio AMP block is okay.
  If AMP is damaged, replace it with a new one.
10-5-3. Service hint (Any picture / Remark)
MIG_SIG
IC206
PCM1808
ADC/MIC_DATA
MCS_MCLK
IC501
MCS_LRCK
MLC3730
MIX_DATA_OUT
< MIC IN function signal fl ow >
ONE POINT REPAIR GUIDE
MIC IN
IC200
MIC
S4308
Board
MCS_BCK
IC202
IR AMP
PS9860
IRS2092+IRF6775
PWM
 
 
 
  MCS_MCLK. pin6 MCS_MCLK. pin6
  MCS_LRCK. pin7 MCS_LRCK. pin7
  MCS_BCK. pin8 MCS_BCK. pin8
  MIC_DATA_IN. pin9 MIC_DATA_IN. pin9
  MIC_OUTPUT. pin14 MIC_OUTPUT. pin14
< MAIN board top view >
3-23
 
 
IC206 IC206