Discussion about the Korg PolySix synthesizer

I recently received a dead PolySix with the dreaded battery leakage problem. 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.

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

The voice LEDs (D10 on KLM-366) do not light when keys are pressed.

How should I proceed?

Thanks in advance,
Alex