No Sound - LG CM4550 Service Manual

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 IC601 to IC701 & 702 each input function.
  If no signal, check if I2S audio signals are entered to IC601.
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 L710, L711, L712 and L713 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 & 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)
ONE POINT REPAIR GUIDE
IC702
IC701
< Signal check point >
3-12
L711
L712
L710
L713