42LC4R, 42LC4RB (CHASSIS:LP78A) - LG TV Service Manual (repair manual). Page 19

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1) After once shining, it does not discharge minutely from module. 
2) The relay falls.(The sound is audible “Click”.)
3) It is converted with the color where the front LED is red from green.

Is the Power Board

normal ?

Replace Power Board.

Is output the normality Low/High
voltage except Stand-by 5V?

Yes

No

No

Is the each

connector normal?

Replace the connector.

Replace the fuse.

Replace Y-Board.

After connecting well each connector,
the normality it operates? 

Yes

No

No

Is the Y-Board

normal?

Is the fuse

(FS2,FS3) on Y-B/D

normal?

Is the output voltage
normal after remove P1
connector of Y-B/D?

Yes

No

FS101,

FS102

No

Replace Z-Board.

Is the Z-Board

normal?

Is the fuse

(FS1,FS2) on Z-B/D

normal?

Is the output voltage

normal after remove P1

connector of Z-B/D?

Yes

No

No

Is the X- Board

normal?

Is the

output voltage

normal after remove P1, 2,

3, 4, 5 connector of

X-B/D?

After remove P1, P2, P3 output voltage
normality: Replace Right X-B/D
After remove P4, P5 output voltage
normality: Replace Left X-B/D

No

Yes

Replace the fuse.

Yes