Hey guys I have kind of solved this but I thought I should post anyway.
So I went in to service this 4K and all channels were super hot and distorted
without the peak light coming on. They desk kind of worked with the
channel thumb wheel set to any group (no matter where that group fader was
set oddly enough) with a lot of noise on the quad buss.
So after some head scratching, by-passing the computer
and taking some measurements of VCA voltage at fader wiper, computer
send and return etc, I read -17 volts at the thumbwheel input on the
channel VCA card thumbwheel input! Normally that voltage would be
0-5v.
So after talking to the famous Vinny Fast and looking at the center section
schematics, I replaced the 20 card with a spare and the problem went away,
So I believe I tracked it down to a couple parts on the 20 card I will be back
with my findings...
