LG CK57 Service Manual page 49

NO SOUND
There is no sound output by DIGITAL AUDIO AMP DAMAGE, repair the set according to the following
guide.
5-2. BY DIGITAL AUDIO AMP DAMAGE (IN ALL FUNCTIONS)
5-2-1. Solution
Please check and replace IC701, IC702 on MAIN board.
5-2-2. How to troubleshoot (Countermeasure)
1) Check PWM_FL±, PWM_FR± & PWM_SW± signals from IC700 to IC701, IC702 each input function.
 If no signal, check if I2S audio signals are entered to IC700.
Refer to "I2S audio signal interface" on Item 5-1.
2) Check PVDD.
 If PVDD is abnormal, check the SMPS.
3) Check +12 V for driving the gate of AMP IC.
a. All the powers are normal, but if +12 V is low, there is possible for AMP IC to be damaged.
b. Remove L702, L703(FRONT), L701 and L704(WOOFER) one by one.
When removed a inductance, if +12 V is recovered, the IC connected to it was damaged.
c. Replace the IC with a new one.
4) Check the impedance between IC701/IC702_OUT_A/OUT_B/OUT_C/OUT_D & GND.
a. If the impedance is 0 Ω, the IC must be damaged.
b. After removing the heat sink, replace it with a new one.
5-2-3. Service hint (Any picture / Remark)
OUT_A OUT_A
ONE POINT REPAIR GUIDE
OUT_B OUT_B OUT_C OUT_C
IC702 IC702
L703 L703 L702 L702
< MAIN board top view >
OUT_B OUT_B
OUT_A OUT_A
OUT_D OUT_D
IC701 IC701
L704 L704
3-12
Copyright © 2018 LG Electronics Inc. All rights reserved.
OUT_C OUT_C
OUT_D OUT_D
L701 L701
Only for training and service purposes.