Ampeg SVT 400 T Distortion

[vbsproul]

I have a SVT 400 T that will produce extreme distortion when the Slider EQ circuit is activated. It works great as long as that function is not used. The pots(Low,Mid,Sweep, High) are smooth and do not make any noise when rotated. I have installed a new cooling fan and have done a grounding modification to it that Ampeg sent me. It was doing this before the mods. Both the Low and High boost switches work. Any ideas. Mark