Yamaha dgx 620 no sound

Yamaha dgx 620, powers up, displays everthing ok. When press style button the style playing leds shows that it is playing but no sound from speakers and even headphones. Playing keys also no sound. What is wrong?

There is no easy way to tell what is wrong without having the keyboard to test. It could be something simple like a bad volume pot, or an unplugged wiring harness. Or it more likely is an electronic problem on the amp board, or perhaps on the main board, or in the connection between them… There are lots of possibilities, and no way to find the answer without doing some testing.

I checked voltages to main board, and found to be 5.02 V and 4.98V from each voltage regulator located on power supply board . On main/mother board I found out that some circuits are supplied with 2.8V. Is this normal? I suspected low voltages. On part of audio i followed audio with my earphone all the way to small audio IC 4580 on main board. No sound. 4580 input is also not receiving any sound.