LG CMS8450F/W Service Manual page 48

ELECTRICAL TROUBLESHOOTING GUIDE
No AMP output
Is the
C904 Voltage
about 390 V?
YES
Is F911 normal?
NO
Replace F911.
NO
Is Q905~Q906 OK?
NO
Replace Q905~Q906.
NO
Is the
PFC P.CTL OK?
Is the
VCC 12 V supplied to
IC904 pin16?
Check or replace
IC904, Q907~Q910.
YES
Is the
AMP P.CTL OK?
Is the
VCC 12 V supplied to
IC902 pin8?
Check or replace IC902 and
Check Q905~Q906 gate(pin1)
Components (Resistors, Diodes).
3-27
NO
YES
NO
YES
NO
YES
NO
YES
Check PFC P.CTL from μ-com.
Replace D908, Q955, PC903.
Check AMP P.CTL from μ-com.
Replace D908, Q956, PC902.
Check or replace D954~D955.
Check line of MAIN PCB is short or not.