music keyboard

Hi. I have a 1992 Ensoniq KT76 digital piano. It works, but the output volume is very very low, even when the volume fader all the way up (no noise from fader), either through earphones or the 1/4 jack outputs in the back, so i'm thinking something might be wrong with the amplifier inside? Could...

My wife's which she uses as a piano. We've had it about 14 years. Maybe it doesn't owe us anything. Managed to fix quite a few snags but a bit stuck now despite my electronics background as I just cannot find a specific Schematic. This is weird! It works perfectly well on external power yet when...