My pioneer sx-315 audio reciever turns on for a few seconds and then automatically shuts off... Is there something wrong with the power supply? Does anyone have a schematic?

The problem you are having is the unit is going into protect.

You can try disconnecting all the speakers and then see if it turns on. If it does turn on you may only have a bad speaker.

Then just turn the unit off and plug in one speaker at a time. If it still turns on, that speaker is good. Keep doing this with each speaker until it goes into protect again, and then you know the last speaker plugged in is the bad one. Make sure you turn it off after checking each speaker.

If it still goes into protect with all speakers disconnected you most likely have a problem in the amplifier circuit.

I have the complete service manual in PDF format with parts list and schematics, but it cost $10.00
Let me know if you want to purchase it and I will give you instructions for that. I can give you a direct download link after purchase using PayPal.

If you would like any further help just let me know.

Dave