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.
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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