OBERHEIM SYNTH

I have an 8-voice OBXa and have a couple of nagging issues I haven't been able to resolve.  

First, I seem to get some slight distortion from voice board #8.  If I move the board to 
another location, it sounds fine.  If I move a known good voice board to the #8 position I 
get the same distortion.  It is most obvious on the organ-type sounds.  I have been using 
it as a 7-voice until I can track down the problem.

Second, if I play the chord "G,C and Eb" in the middle octave of the keyboard, it also 
sounds the "E" below the G.  Needless to say, this can be annoying!  Must be something 
having to do with the keyboard scanning, but I don't know what exactly.  The double mode 
also doesn't seem to work 100%.  Maybe a related issue?

Any thoughts on what might be causing these and how to fix them?  I have the schematics, 
but I don't really know what I'm looking at since I'm not a tech.

Thanks for any help or advice!

Jonathan