LG CM9750 Service Manual page 43

NO SOUND
There is no sound output in the Bluetooth function, repair the set according to the following
guide.
10-6. BLUETOOTH FUNCTION
10-6-1. Solution
Replace IC501 on the MAIN board or B/T module on the Front Panel.
10-6-2. How to troubleshoot (Countermeasure)
1) Check BT_RX, BT_TX signal to pin4, 6 of CN504.
  If no signal, Check the signal to pin4, 6 and pin10 (+3.3 V) of on the Bluetooth module and cable
connection state.
  If there are no signal out from module, replace new module.
2) Check if BT_RX/TX is entered from pin4, 6 of CN504 to pin K1, L1 to IC501 (DSP).
3) Check the following I2S signal flow from IC501 to IC600.
  If there is any trouble, check the power for each IC. If the signals are abnormal, replace it a new one.
4) Check if the digital audio AMP block is okay.
  If AMP is damaged, replace it with a new one.
10-6-3. Service hint (Any picture / Remark)
B/T Module
BT_RX,
BT_TX
IC501
MLC3730
< Bluetooth function signal fl ow >
ONE POINT REPAIR GUIDE
IC202
PS9860
PWM
MCS_BCK
MCS_LRCK
MIX_DATA_OUT
IR AMP
IRS2092+IRF6775
BT_TX. pin4 BT_TX. pin4
BT_RX. pin6 BT_RX. pin6
< MAIN board top view >
3-24
CN504 CN504