So, it appears my HK AVR 7300 isn't truly Lazarus, risen from the dead but more like Rip Van Winkle rising from a nap. Here's the symptoms:
It had been sitting plugged in but unused for a longggggggg time. At least a year, maybe two. When I first turned it on it ran for a minute and shut off. Then it ran for a few seconds and off. Then nothing. Sounded like a bad cap to me so I spent months looking for schematics. Once I got them I discovered the problem is now the reverse. If I press the power button, which is white (IIRC) on standby at first nothing... not a click, not a change in color to indicate it's on, zero. BUTTTTTTTTTTTTT if I push it several times it will begin to first change color... then the first relay clicks after a few tries... then after a few more the second relay and the display comes on... and finally it fires up. Just like a car that's been sitting for ages. Once it starts up, if I start it daily, it's fine. One click and it's on. Soooooooooo if you're still with me this far (thank you!), I'm thinking it's a cap early on in the circuit. Attached is a schematic with my guess but since disassembly is a horror show I'd love any other opinions.
Thanks a million!

 

Check the 5V standby line for proper filtering. Also the driver transistor(s) for the relays might be defective. With the unit working as expected if used daily, it suggests that there are caps starting to fail as you mentioned.

Dan