Try jeff@nakamichi.us. I think thats his website. He has been repairing these decks for years. I bet he could steer you towards finding a manual or least copy of one.
Unfortunately Nak has become more mass cheap electronics but if you find a kind soul in the company they should be able to dig you up a copy.
I might have the original laying somewhere but trying to find it it another thing. hehe.
Happy listening,
the Prisoner