What's missing, the logic control signal to the BJT's for the PWR ON relay ? Or the Vcc that would be on C2206 in that 1st manual ? Where's that Vcc com from, some 3-pin regulator or little circuit from a StandBy rail ?
I'd start with it turned off, with a DMM I'd check over all the power rails, and Vcc rails on each board. Then I'd make sure the relay circuit itself is working, I might discount some of the boards or cut power to sections , just until I was sure the PSU section is ok.
So why did you get the Stereo? For fun, profit, learning experience, /etc ?
I bought 1 used stereo last winter, and it had problems on day 1, but I kept it for fun and to learn more about them. Some of the input chips on mine are acting up, and /or the main MCU. So I'm programming my own MCU to help out, when my stereo doesn't do what it should be doing.