Yamaha CS80

Hi all.

When I just put in another Kenton board (very late SN# CS80),
something looked strange to me. There was a PC Board with a bunch of
diodes on it attached to the inside of the front panel, next to the
Sub Osc levers.

I didn't remember seeing that board before. So, I pull up all the
pictures I've taken of the insides of the CS80s I've worked on and see
three different versions!  Some have no board there. A couple have a
very small board, and the one that caught my eye is the only one with
the larger board.

I've put all the pictures in the folder "mystery board" under photos.
Can someone tell me what the deal is with these?  Inquiring minds want
to know :^)

Thanks,

 DAvid