Yamaha CP30 repair

Hi there,

My Yamaha CP30 has a constant random crackle which is present even when no notes are pressed. Its volume corresponds to the master keyboard volume, and decreases as voices are turned off. With all voices off, there’s still a faint noise but this is manageable.

I have an oscilloscope and tentatively know my way around electronics, but I’m not sure where to start.

Is there something common that dies with these keyboards over time? Should I just replace all of the capacitors as a matter of course?