Check the fusing resistors on the 82E20 card which would be R22, R60 (Ch 6) and R24, R62 (Ch8).
I've had these blow out, along with the associated transistors, T15, T27, and T17, T28.
This part of the circuit controls the voltage to the VCA bus.
If you have a computer, run !TES and see if the computer responds to the VCA faders under the Input test page.
Anthony.