Denon AVR-1604 too large front speakers blew the avr
Try disconnecting the speakers at the receiver. turn it on radio or any other source and turn up the volume. If the receiver still shuts of, there is an internal capacitor issue and needs serviced. More than likely though, it's a speaker problem. If the speakers were underpowered and at max volume, chances are the damage was to a voice coil in one of the speakers. If the receiver continues to stay on without being connected it's ok. check your speaker wires as well. Frequently loose braids on wires touch each other and create very little resistance until turned up, more volume, more resistance. Then the receiver puts itself into protection mode so no damage will occur. If you need further help, post a comment and I can help you troubleshoot further.