I use the SM from Sensos synfo.nl:
http://www.synfo.nl/servicemanuals/Korg/POLYSIX_SERVICE_MANUAL.pdfand a camera-"scan" I did myself, from an original
http://fa.utfs.org/diy/korgpolysix/polysix_service_manual.pdfThe file from Sensos site, which is very black&white trimmed, is better
for overview. In my photography based copy, which is more gray scaled,
some details are better readable.
About your problems: I have recovered a battery damaged P6 some months
ago, it had some high frequency noise too and I found that much trouble
comes from bad grounding. Also you should whatchout that the cables from
the keyboard do not cross the audio board. Korg has bent them carefully
along the corner of the board.
And last but not least:
"It throws a high pitched whine like the freq envelope is has a slow
attack. "
I don't understand, what this sentence shall mean. I am german, so maybe
this im my fault, but to me this is not really clear English. Please try
to explain it with some other words.
Florian