UPDATE: by tweaking the envelope amount polarity control WAY over I was suddenly able to get some sound - even after tweaking the envelope controls a bit. Though I wasn't able to get and timbral change happening by messing around with other controls apart from frequency, etc... but I was able to get different pitches out of different keys...

UNTIL

then suddenly the mono-poly just started emitting constant (distorted) audio, having entered the UNISON mode on it's own. Key presses affect nothing. Then Key Assign Mode LEDs all dead and buttons unable to control anything.

WEIRD HUH

I'm not sure where to go on this - i guess look at the key assign circuit... though it could be just a byproduct of something wrong with the CPU