I have a Korg Mono/Poly with a strange error.

When I turn on the MP4, it looks like everything is fine, but after some seconds all LEDs turns on (for all VCO, Key Assigne buttons, Effect), Sometimes the one or two of the OSC LEDs kan start to flicker. Nothing happends if I press any of the "Key Assigne" buttons. If i turn on the volume to maximum and set the "Output" switch to high I get some kind of noise sound and it doesn't matter what key I press on the keyboard, I only get this noise sound.

Anyone idees what it could be