I can't really help with this too much. Except for this...
Google search for H||H VS Musician schematics. That is H||H stuff that can be found for free with simple search and the diagrams should be online at least on some of the found links (though not all of them and frankly I'm too tired to search for the working ones). At least the power amp designs from that particular era seem to revolve more or less around the sort of design found from those diagrams and not too much of the stuff should be different. Can't say anything about the preamp, they shouldn't be rocket science either so finding basic faults from everything else but the potted modules shouldn't be excessively difficult.
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