LG 40LX770H Service Manual page 24

8. AV/Component Audio (in) Trouble shooting guide
Check input signal format.
Is it supported?
Y
Check AC cable for damage
For damage or open conductor
Y
Check JK3402
Can you see the normal waveform?
Y
Measure waveform at C3404, C3405, C3406 because it's more easy to check.
Y
Check Audio AMP output
L5602,L5603,L5604,L5605
Y
This board has big problem because Main chip (M14+) have some troubles.
After checking thoroughly all path once again, You should decide to replace M14+ or not.
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Only for training and service purposes
N
Check the input of M14+(IC101).
Can you see the normal waveform?
N
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Replace JK3402
Replace L5602,L5603,L5604,L5605
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