hifi engine

Need service manual and/or schematic for JVC KD-A77 cassette deck

Hello Everyone,
I'm looking for service information for a very nice 1980-ish top-range JVC 3-head full-logic cassette deck that a mate gave me.
I've seen the schematic on other paid sites, with prices ranges from $9 to a "go fish!" $24.
The machine seems to work OK, but the lighting seems a tad dim and it stopped once on me recently for no good reason (tape was OK). Also the meters seem to read a tad low, and the sound is rather soft/mushy with a noticeably dim treble range. I also have heard the treble jump up a bit momentarily, all of which suggests an iffy PS rectifier diode, or maybe even a regulator.
Any help with this would be gladly appreciated, but you knew THAT!