The DGX-530 and YPG-535 models by Yamaha® are virtually identical
This particular DGX-530 had all its lights, buttons, and display
functioning properly but there was no sound from the built-in speakers or the phones output.
The speakers and phones are driven by an audio amplifier IC, the LA4625.
An electrolytic capacitor connected to pin 2 of this chip was faulty, causing
the IC to shut down.