Vintage Synth Repair

> You may remember I asked about a Korg Poly 800 with damage from
> a leaking battery a few weeks ago. Well, the bicarb and toothbrush
> technique has cleaned it up reasonably well, but there are other
> problems now.

You might want to test to the continuity between the CPU and the memory
chips for all the data/address/control lines and at the same time make sure
there are no shorts to other data/address/control lines.
 
> The CPU is an 80C85. Is this chip still in production or does
> anyone know of a surplus outlet who'll sell a one-off at reasonable
> cost?

Is it in a socket?  If it's not, put it in one (well, the replacement IC).
What's the whole part number on it?  Do you have schematics? I'd
like to see them.  You might be able to find one on ebay, although
you might also have to buy something that has one on/in it.  I don't
know of anyone that has them off-the-shelf.

GB