LG Electronics 55LA790V/W/9-ZA LCD TV , First of all, Check whether all of cables between board is inserted properly or not.

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Normal
audio
Y
N
Move to No
video/No audio
No video
Normal audio Check Back Light
On with naked eye On Y
N
Check Power Board
12v,3.5v etc. Normal
voltage
Y
N
Replace T-con Board
or module
And Adjust VCOM
Repair Power Board
or parts
Check Power Board 24v output
Normal
voltage Y Replace Inverter
or module
N
Repair Power
Board or parts
End
Always check & record S/W Version and White
Balance value before replacing the Main Board Replace Main Board Re-enter White Balance value
※Precaution
Established
date
Standard Repair Process
Revised date
LCD TV Error
symptom A. Video error
No video/ Normal audio
☞A5 ☞A1
☞A5
☞A28
☞A4 & A7
First of all, Check whether all of cables between board is inserted properly or not.
(Main B/D↔ Power B/D, LVDS Cable,Speaker Cable,IR B/D Cable,,,)
2012. 12 .06