[R-390] AGC and Stability

[Steve Hobensack]

I was recently running psk31 and using the r-390a as a receiver. I got some garble in the copy and noticed there is a slight trace wobble in the waterfall that moves with agc action. It is quite stable in MGC. I have changed bfo and pto tubes, the VR tube glows. I do use audio derived agc that is tapped off the line gain but just a smidgen. It still doest it when the line output is off. Where should I look next? 
Thanks
Steve N8YE