2014-12-28 Yamaha RX-V757 Power Supply Fixed
Yay! $0.55 AUD part fixed my Yamaha RX-V757 amplifier.
Turns out, it's a common problem. The amp had survived at least one large power surge (an 11kV line on the power pole outside the block of units had dropped down onto the 415V lines - blew the power board off the wall on a neighbouring block!) and probably copped another one during a lightning storm. After that, the amp failed to power on - no relay clicks, no front display, not much of anything. Opening it up, I found that there was no power going to the main large transformer, and so no power going to the power button. A bit of searching around, and it's pretty well documented, as described in this video:
That was it - I unsoldered C405, which was supposed to be a 22nF metalized polyester film greencap capacitor, and measured it - 1.5nF. Quick trip to Jaycar and bought a 22nF 630V capacitor, measured it (yep, 22nF) soldered it in, and works perfectly.