Read LG 42LH50YD (CHASSIS:LJ91C) Service Manual online
6. RGB Video Trouble Shooting
Check Signal Format
Is it supported signal?
Y
Check RGB Jack JK701
N
Y
Y
Check RGB Cable
Replace Jack
Check RGB Signal
L708, L709, L710
N
Replace It & Recheck
Y
Check Sync Signal
IC702 #11, #3
N
Replace one of R759/R761/IC702
& Recheck
Y
Check EEPROM (IC703)
N
Replace it or re-burn
& Recheck
Y
Maybe BCM3556(IC100)
has problems
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