The ground for the sound board goes through the connectors. Repin those with some new trifurcon pins.
J2 - pin 3,2,8 all point to ground.
Also, check your volume potentiometer in the bottom of the cabinet. I haven't had to replace one of these yet; usually working the knob back and forth clears up static.
And, as others have said; get a cap kit and replace them all.