i have an old scott receiver that i am trying to fix, all audio outputs on the left side (speakers and also head phones) have the same electric humm mixed with the sound. does anyone know what i need to be looking for. what could be causing this
60Hz hum is almost always a ground problem. In this case that is likely to be either a bad capacitor or capacitors (look first in the power supply) Or since the problem is in only one channel a bad coupling cap in that channel. If this is a receiver that has sat unused for any period of time, the caps have probably dried out. There could also be a bad connection in the signal path being caused by a solder joint that has dislodged or severely oxidized/corroded. A worst case scenario is the power transformer could have problems.
Buzz and other noises above 60Hz are typically transistors or other semiconductors having problems. I would first check all the diodes. In short, with a unit that has some age on it, check everything.