There are some JX-8 info and schematics for the JX-3P here;
http://www.synthzone.com/roland.htm

You could try the JX Yahoo group;
http://launch.groups.yahoo.com/group/rolandjxanalogs/

One of these places should have the schematics (for sale);
http://216.239.59.104/search?q=cache...chematic&hl=no

(http://www.musicparts.com/sciman/)

http://www.mglinsky.www5.50megs.com/msg4.html

http://216.239.59.104/search?q=cache...chematic&hl=no