I had this with my old Yamaha (RX-V457) and ultimately concluded it was a dead microcontroller, so it went to the e-waste pile in the sky. Check the processor board is regulating the 5.5V down to 3.3V for the microcontroller. My 3.3V supply was present but all signals on the MCU were dead, including relay on signal, I later found online this does occur sometimes, perhaps power surge damage or bad flash cells degrading. In theory a new board could fix it, but I couldn't source one. The RX-V579 is a much newer generation though so you may have better luck, good luck either way.