Muting Circuit (Mute) Troubles; Audio Abnormal - LG SB74 Service Manual

3. MUTING CIRCUIT (MUTE)
Does "High" appear
at Q206, Q208 "B"?
YES
Check the "Low" of
Q206, Q208 "C"
YES
MUTE

4. AUDIO ABNORMAL

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
Check the FB302
Check the Power Circuit
NO
Check R202,R203
NO
Replace Q206, Q208
YES
YES
YES
YES
NO
Check D205,D204
NO
Check the connection of speakers
NO
Check the "High" of U200 pin7
NO
Check the function input
NO
3-2
NO
Check JK601 pin50
NO
Check R635
NO
Check the IC603 pin81
"HIGH" or "LOW"
YES
Replace IC603
Normal