42LH55 (CHASSIS:LA92B) - LG TV Service Manual (repair manual). Page 25

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1. TV/ CATV
Check TU1 Pin16(SIF)
Can you see the normal signal?
Check the input (Pin W2) of  LGE3159((IC100).
Measure waveform at C147 because it’s more easy to check.
Can you see the normal waveform?
YES
NO
Could you measure voltage of
 TU1001 & IIC lines?
Are they all normal?
NO
You should check power line 
& IIC lines.
YES
You should replace TUNER.
NO
After checking audio signal line,
you should decide to replace item or not.
2. AV/ Component/ RGB- PC
Check JK1206, JK1202, JK1205
Can you see the normal waveform?
NO
JK701, JK707, JK700, JK702, JK703 
may have problem. Replace this Jack.
Check the input (PinAA3,Y1,AE1,AF3,AE3,AE2,AA1
AB1,AB2,AC2,AB3,AC3) of  LGE3159(IC100).
Can you see the normal waveform?
NO
YES
After checking audio signal line,
you should decide to replace item or not.
YES
Check the Output
 (Pin Audio_MASTER_CLK ,MS_LRCK
MS_SCK,MS_LRCH) of  LGE3159(IC100).
Can you see the normal waveform?
NO
After checking audio signal line, 
Check IC600(NTP-3100L) L606/L607
YES
NO
After checking audio signal line,
you should decide to replace item or not.
you should decide to replace item or not.
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