Discussion about the Korg PolySix synthesizer

Hi, I just picked up a polysix with the battery replaced and board cleaned up. Everything is functional. The only issue is tuning. I followed the service manual and cannot get the synth in tune. It seems like the range of the VRs for the oscillators. If the high note C is in tune, the VR maxed out is still not C. And visa versa. After tuning high C at C6 with 4', C2 cannot be set to 0 cents either. It is more like A or A#. The scaling seems off. The opto is replaced with a VTL5C3 that tests correctly and has a fine-tuning resistor that i set at 1k2. Only that that seems weird is that when I put the test lead of my multimeter of pin 6 of the connector for keyboard tracking it shows -5V. VR5 and VR2 seem to do nothing. Help!