I've never found schematics for DSI products. I was about to start reverse-engineering the board in the DSI-2400
Do you have a way to scan the manual that you have and could you take some pictures of the boards inside?
It looks like this was built before they started making their own reader assemblies (it looks like a Decitek reader)
They had been making their own punches for a while.
I was just down a rathole looking at reader assemblies over the weekend and adding a bunch of information
on them to bitsavers.