I rescued a Fender Stage Lead II 2-12 blowing the main fuse. Trying to diagnose.

I have a grainy schematic.

Stage Lead II Schematics

I started with a dim bulb tester.

I have disconnected the preamp and controls, leaving only the power amp connected. Still a bright light (fuse blower). The power amp section has a fused lower-voltage section and an unfused higher voltage section (~63V, +/- ~34V). When the 63 V section is not getting power (wires pulled from molex connector), the fault goes away. When the fuses for the low voltage section are fulled, the fault persists. Voltage measures correctly on transformer leads (63VAC) when disconnected so the transformer looks OK

When in fault mode with the dim bulb tester in place, the AC voltage across the big rectifier is 2VAC if thatr is any clue.
 
Any suggestions for hunting the faulty parts? All of the electrolytics show well in range on my ESR meter, no shorts or open. Nothing obviously burnt. Not a lot of parts there!

I'm focused on the schematic on the bottom half of the second page on the linked images.