Vintage Synth Repair

I recently received a dead Korg PolySix. The battery was replaced and the damaged traces were cut out and replaced with 30AWG wire. Currently when the synth turns on, the LEDs briefly light up and then go dark except for Program 1 and Bank 1. As they should.

There is no sound, however. Only hiss. When I turn up the volume pot, the hiss gets louder.

The voltages all match the schematic.

I suspect something is awry on the KLM-366 board.

Any tips on where to look first?