Discussion about the Korg PolySix synthesizer

Hello-
I've been handed another battery-damaged Polysix to repair;  what's 
different about this one is that it contains a MIDI board that appears to 
be from Korg --
it's labelled "KORG USA"  "Polysix MIDI Retrofit".
I haven't come across this particular board before;  does anyone have any 
idea where to find documentation for it?
Thanks.

~GMM