Hey look for bad Filter Caps on the PSU , and bad e-caps on the main board as well. Check for bad solder joints on the jack pack board they usually see alot of action from being plugged and unplugged.
I wold start here first.
All so check the vcc pin at the audio processor and audio IC.
If no or low voltage is present lift the vcc pin and retest the voltage.
If the voltage returns after you lift the vcc pin the suspect the IC is bad and replace it.
and of course if it is still not there or low , the you have to start tracing it back to the component that is bad.
