Korg Wavestation Ad Hoc Silence

[Bongomeister]

I have a Korg Wavestation, owned it for years, have recently relocated overseas and after getting it out of storage and setting up I'm finding that its silent on only certain sounds (e.g Midi grand and Warm Strings etc). Go up or down one and it works fine. Never had this issue before.

I am running a standard data and a piano program card. I've done the Init RAM and replaced the internal battery but it hasn't changed. Any ideas?

Thanks