Read LG 42LH50YD (CHASSIS:LJ91C) Service Manual online
8. HDMI Video Trouble Shooting
Check Signal Format
Is it supported signal?
Y
Check HDMI Jack
JK500, JK501, JK503
N
Y
Y
Check HDMI Cable
Replace Jack
Check IC601 Voltage Level
+1.8V_HDMI, +3.3V_HDMI
N
Replace one of
L601/L602/R665/R663
Y
Check I2C Signal
R670/R671
/R605/R606/R616/R617/R639/R64
2
N
Replace It & Recheck
Y
Maybe BCM3556(IC100)
has problems
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