Discussion about the Korg PolySix synthesizer

hi everyone i have a korg ploysix background unknown but the battery 
has been replaced and the boards seem to be working(leds lit).but when 
i connect headphones or amp to output all i get is a faint hum,and no 
sound regardless of which keys or presets i select.is this a common 
fault ?.thanks any pointers in the right direction would be great.