Being older, as in "Pre-Klipsch buying the company", I doubt you'll find one. They didn't generally have many manuals for subwoofer amps and when they went bad under warranty, they replaced them, kept the old ones and sent them to a few service shops for repair, just to have them on hand for out of warranty situations.
Have you tested the speakers to find out if they're not the cause? Is it possible that the cable unplugged at one end or the fuse is blown?
A good service tech should be able to find the problem.
