LG LST-4200A Service Manual - Page 45

NTSC Front-End part

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7. NTSC Front-End part START YES NO Is power charging normal? YES Is RF input signal normal? NO (Use spectrum analyzer) YES Check voltage between R511 and NO earth. 5V : Abnormal(Bad), 1V ( below) : Normal YES Check video output signal of NIM NO Tuner Tuner(IC500)(pin 16, Fig.04). YES END Check power line, referring to circuit diagram. (+5V_Alive, +5V, +30V, +1.8, +3.3V) Check antenna connection condition. Replace Q501, Q502. Replace tuner. Fig.04 IC500(16) NTSC Video Output Signal 3-36

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3-36
7. NTSC Front-End part
Is power charging normal?
Is RF input signal normal?
(Use spectrum analyzer)
Check voltage between R511 and
earth. 5V : Abnormal(Bad), 1V
( below) : Normal
Check video output signal of NIM
Tuner Tuner(IC500)(pin 16, Fig.04).
Replace tuner.
END
START
Check power line, referring to circuit dia-
gram.(+5V_Alive, +5V, +30V, +1.8, +3.3V)
Check antenna connection
condition.
Replace Q501, Q502.
NO
NO
NO
NO
YES
YES
YES
YES
YES
Fig.04
IC500(16) NTSC Video
Output Signal