Need a circuit diagram for a Pioneer AV Receiver VSX-523

I'm working on a Pioneer VSX-523 for a friend, and it keeps shutting off consistently after turning it on for about 3 to 5 seconds. There aren't any indicators telling me what the problem is, and the situation doesn't match anything in the manual's troubleshooting section.

Does anyone have access to a circuit diagram for this particular receiver or any advice about this type of receiver? It would be appreciated!

Thank you.