LG SB74, Service Manual

Page: 13 / 39

3-2
3. MUTING CIRCUIT (MUTE)
NO NO NO
Does “High” appear
at Q206, Q208 “B”?
YES
Check D205,D204
MUTE
Check R202,R203 Check JK601 pin50
NO
Check the “Low” of
Q206, Q208 “C”
YES
NO
Replace Q206, Q208 Check R635
4. AUDIO ABNORMAL
NO
YES
YES
Check the connection of speakers
NO
Check the “High” of U200 pin7
NO
Check the function input
Check the output of U200 pin1,2,14,15
Check the input signal of U200 pin4,12
Check the DC 12V of U200 pin3,13
YES
NO
Normal Check the FB302
Check the Power Circuit
YES
NO
Check the IC603 pin81
“HIGH” or “LOW”
YES
Replace IC603