Most sites on the net want to sell you the diagram/manual. Here's a link about your PL and perhaps you can contact them for further assistance: **broken link removed**
Also, this schematic may be close to your model: **broken link removed**
Here's a master list of Phase Linear service info.: **broken link removed**
Phase Linear made some excellent, high end equipment in their day. I own a preamp of theirs and sonically, it's superb, even better than my $500 Soundcraftsman. Your PL is worth restoring if money allows it. Equipment like that and that of other esoteric brands from the 70's & 80's have a classic character all of their own, compared to today's garden variety junk that lasts only a few years. I hope this information meets your needs. Good Luck.