19LN4050 (CHASSIS:LB35A) - LG TV Service Manual (repair manual). Page 10

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TROUBLE SHOOTING
1. NO POWER-Main PCBA
Is Adapter 
Output VOLTAGE 19.4V
through of JK700?
NO POWER
Is 3.3V at C708?
Check waveform of X501 
YES
NO
YES
NO
YES
check open or short at Line.
or change Adapter.
check the Lines of IC701,
If there is any problem at Line, 
Change IC701
NO
Check Line short or open between 
IC501 and X501,
Change IC501 or change X501
1
2
4
Is 1.8V at C745?
is 1.25V at C742?
3
YES
check the Lines of IC711,IC704
If there is any problem at Line, 
Change IC704,IC706.
NO
Insert F/W
is 3.3V at 1pin of P120?
when push power key,
Is 0v at 2pin of P120?
Change control
Or check Line short or open of P120
5
is there any waver at 11pin of P120,
when use remote controller? 
6
NO
YES
change IR board
Or check Line short or open of P120
NO
4
X501
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