LG CM9520, Service Manual

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3-29
ONE POINT REPAIR GUIDE
NO SOUND
There is no sound output by DIGITAL AUDIO AMP DAMAGE, repair the set according
to the following guide.
6-3. BY DIGITAL AUDIO AMP DAMAGE (IN ALL FUNCTIONS)
6-3-1. Solution
Please check and replace IC701, IC702, IC703 on MAIN board.
6-3-2. How to troubleshoot (Countermeasure)
1) Check FL±, FR±, RL±, RR±, SW1±, & SW2± signals from IC602 to IC701, IC702 & IC703 each input
function.
If no signal, check if I2S audio signals are entered to IC602.
Refer to “I2S audio signal interface”.
2) Check PVDD_50V.
If 50 V is abnormal, check the SMPS.
3) Check +12 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 a ferrite bead among FB703, FB707 and FB713 one by one.
When removed a ferrite bead, 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 SPK+ & GND and SPK- & 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.
Comments !!
If a AMP IC among three is damaged, “AMP_PDN” to R103 changes HIGH to LOW at regular intervals.
The sound is not output by AMP power down function.
6-3-3. Service hint (Any picture / Remark)
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< Signal check point >