LG LST-5600A Service Manual page 31

(D)
Check NTSC mute signal is low.
OK
Check HD-II NTSC encoder part.
OK
Check NTSC analog output buffer part
NO
End
NG
NO
Check power:IC604(8); +5V IC604(4) ; –5V
NO
Check composite: FIG.16 top, Input:
IC604(3,5) Output: IC604(1,7)
3-24
Check Q501 base voltage.
Must be low.
If not, check IC201 pin 47
Check NTSC encoder pixel clock:
IC605(13) FIG.15