My Korg PA800 suddenly started making hissy noise. I usually switch it on a few hours every day. It was ok until about 8 pm on the day. When I started to play about 11pm on the same day (the keyboard was ON all the time) it started giving hissy noise like an untuned FM raido. It comes with all instruments. The noise increases when the volume is increased. I have reloaded the OS to latest after formatting. The noise still didn't stop. What could be the problem? Will it be a power supply issue or Power Amplifier or even the main board ? I opened it up and didn't see any physical leaked capacitors. Can anyone help me on this ?

That does not sound good!

Possibilities:

The D-A convertor is going bad. The hiss could be digitizing noise or noise in the conversion network within the chip.

Noise in a preamp op=amp chip.

Noise in a passive component such as resistor or diode.

Bad plated through hole in circuit board.

The power supply is NOT very likely and since volume affects loudness, teh power amp is NOT suspect..

Troubleshoot this IMMEDIATELY using circuit cooler to isolate bad part.

A tiny squirt on suspect components till you hear a change... then gentle warming with hair dryer till you home in on the part...

I SUSPECT you will find the parts are mostly surface mounted... IF you have not had experience in replacing these before, better take it ot a shop that is equipped to do this.