Oh well.
I removed the battery and there was a fair amount
of corrosion there. Nothing had been eaten through but the tell-tale brown
discolouring was present. I had to wire-link several components just to be on
the safe side but the machine is still unwell.
Poly8 mode produces the most sound although it is
sporadic and most of the keys dont seem to sound. Poly4 mode produces a high
pitch static sound like the filter on full resonance over any faint sound that
may be there. Mono mode now is just a shrill digital fuzz.
Im beginning to suspect one or more IC's may be
faulty but i don't have a clue which ones.
I think it maybe time to hand it over to a tech who
knows what he/she's doing!
The only problem is, i don't know of
any!!
Anyway, thanks to everyone for the help.
I just hope i can find someone to get this thing working!!