Discussion about the Korg PolySix synthesizer

More thoughts.

Both the "B" and "2" LEDs are served by D01.

D01 is also used by the Subosc switch (and the Mod switch); however the
Octave switch (and the Waveform switch) use D00 (if the documentation is
correct; I haven't checked this with the PCB yet).

D01 comes from pin 6 of IC31. It should also connect to the R17 array.

IC31 also should connect from pin 12 to the processor pin 13.

Seeing that IC31 and its traces are usually most affected by the battery
problem I'd look for the problem there first.