Discussion about the Korg PolySix synthesizer

hello it's me again.

well so far it looks like it's quite possible that the main cpu is
faulty. the full label is
NEC PD8048c-345
i have a few questions:

does this microprocessor have internal PROM? if so - do we have a
binary for it? how would i go about programming it? anyone ever did
that?

any idea if it could still be available somewhere? any known substitute?

anyone got any of those spare? from a broken polysix maybe?

best regards,
jure