Archive of the former Yahoo!Groups mailing list: Discussion about the Korg PolySix synthesizer

Contrary to what you say the battery clearly has already leaked, just not
as bad as with many other cases.
The greenish residue around the vias and IC31 legs is a clear sign, so are
the dark spots on the large trace near the battery.

You should remove the battery at once and give the board a thorough
cleaning. Perhaps the board still can be saved.