My Oberheim obxa had a similar problem and the CPU was broken. It has been checked in the Netherlands, but they could not find the problem. In the end I brought my obxa to Germany Oberheim Mellotron Novatron Simmons Kurzweil Oberheim Mellotron Novatron Simmons Kurzweil Erfahrungsberichte, Tipps, Technik, zu Mellotron, Novatron, Oberheim, Simmons, Kurzweil, Midi-Controller View on www.blue-jet.de Preview by Yahoo and he is very nice and could fix my obxa.Please try to change the CPU at first.