I have recently purchased a Korg Ms20 from the US. It all seems to be in fine working order although i have had to use a converter for the two pin American plug. But after a while of adjusting the frequency modulation the keyboard no longer plays and I just get what sounds like a slow portamento on ...

I have recently purchased a Korg Ms20 from the US. It all seems to be in fine working order although i have had to use a converter for the two pin American plug. The problems occur when i set the highpass and low pass filter peaks to 9 or ten. The sounds changes to a constant drone and i can no long...