LG CM9550 Service Manual page 37

6. NO SOUND
There is no sound output in the USB FUNCTION, repair the set according to the following
guide.
6-1. IN THE USB FUNCTION
6-1-1. Solution
Please check and replace IC501 on MAIN board & IC300 on USB board.
6-1-2. How to troubleshoot (Countermeasure)
1) Check +5VU to USB board.
  If +5.6 VA to pin2 of IC300(LDO) doesn't come out, check pin4, 5 of CN304.
  If +5.6 VA is normal & +5VU of IC300 pin3 doesn't come out, then replace IC300.
2) Check if "Digital audio AMP block".
6-1-3. Service hint (Any picture / Remark)
MCS Interface
16.9344 MHz
LC78615ERF+ SERVO
USB_HUB_DP/DN
EN
(+3.3 V_CD, VCC 1.2)
MIC CODEC
MLC3730
MCS LOGIC
ADC CODEC
24 MHz
PWM_MCK/BCK/
MIC_O_DATA0
12.288 MHz (+3.3 V)
X/RX
CS/MCU_RST
TAS5548
I2C/EXT_MUTE/RST
PWM
SPENA
Front : 470 W X 2 ea
Woofer : 460 W X 2 ea
Front1 : 470 W X 2 ea
< USB function signal fl ow >
ONE POINT REPAIR GUIDE
USB1 USB2
(+3.3 V_USB)
BT
MIC_SIG0
MIC_DET
BT_RX, BT_CTS
MIC_SIG
(+5_MIC)
MIC
S4308
DAC_MCLK
(+5 V,
+3.3 V_ADC)
/BCK/LRCK
ADC_DATA PT_L/R
CS5346
Portable
AUX_L/R
AUX
TUNER_L/R
(+3.3 V)
TUNER
CLK/DAT/CE/RST/GPO2
LRCK
AGL_F/R
FL
FL± FL
DAC IC FL
RL
RL± RL
AZ4580
RL
FL1
DRIVER
FR ± FR FET
DAC IC FR
IRS2092
IRF6775 FL2
RR ± RR
AZ4580
(x 4 EA) RR
(x 12EA)
SW DAC IC SW SW1
SW1
AZ4580
SW2
SW2
AMP_OSC
TH
AGL_SW
PROTEC /
SD/DCP
FAN_CTL OTW
D+
D-
< Waveform of USB D± signal >
USB D+ / D- (CN502 Pin1, 2 & 9, 10)
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