SONY FH-7 III humming sound(fix)

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fyj2972

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Symptoms: Background humming or buzzing noise from speakers even volume is at lowest setting.
Check ACU-78 power supply unit: +/-32v +/-20V and +21V output are normal . Five 2200 mpd filter caps ESR readings are perfect.
now what?
Short both amp STKs inputs in TA-78 to ground, Humming is gone, I disconnected D108, then feed 20V(pre-amp 18V source) with pure DC through D107. Humming came back. This time I am sure its not ripple cause humming.
Well, Attack EQ section. ($%$&#@%&*&(^) save your time)... after replacing IC102 (M5218) with NE5532. Humming is not there anymore.
Gottcha, radio is fixed. :)))))
To be honest, OP IC goes bad is very rare, But It happens.
Just share my 2 cents, Thanks for reading.
 
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