19LN4050 (CHASSIS:LB35A) - LG TV Service Manual (repair manual). Page 16

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7. Abnormal sound (TV)-Main PCBA
Put into RF cable completely?
Abnormal sound (TV)
YES
NO
insult RF cable tight and then 
Cable nut screw tight.
1
2
3
4
NO
Change Main PCBA
WAVEFORMS
Is 1.8V at 7pin of TU401?
Is I2C waveform 
At 3,4pin of TU401?
Is IF waveform at 43
,44 pin of IC501?
NO
NO
3
3Pin of TU401 (SCL)
4Pin of TU401 (SDA)
4
43,44pin of IC501
If 1.7V is not at plus pin of TU401,
check It is over 3V at 2pin of IC401, 
if it is not, Check Line between TU401 
and IC401 is open or short.
Another is change IC401 or TU401
Check Line between TU401 and IC501
is open or short,  Another is change 
IC501 or TU401
Check Line between TU401 and IC501
is open or short,  Another is change 
IC501 or TU401
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