The pinned topic has schematics in still images, this one is a beautifully composed PDF. All the notes are in japanese, however. Still, it should be much easier to search in this one.
Original source: http://green.ap.teacup.com/junker/25.html
The guy who did this has a ton of other stuff up there, including schematics for the 4mb ram expansion, or the kof95 rom cart. Since the kof95 rom cart is now dumped, it may be possible to build that cart with the schematics.
There's also much more research there, such as gigantic in-depth tables detailing the differences on various different Saturn motherboards, etc.