crackles when playing 2+ notes

I've been gifted this Casio small keyboard (don't know the model - it's prolly a 7xx or 8xx). It works fine except if I press two keys at once. Then it sounds crackly.

I suspect it's a chip problem. Anyone experienced this / got any ideas how to fix? I'm sure it's off warranty.

I would bet money I'd need to find and re-solder a chip or soemthing.

Just a thought...Crackly \ distorted sound is also possible if the correct mains adaptor is NOT used which is not providing the specified current to the keyboard.

[This message has been edited by Graham UK (edited 02-11-2008).]