I found the possible bad components on the schematics. I do believe all these components are socketed.

One problem we had with dip sockets with old coin op video games (all digital) was that the sockets would build up an oxide between the pins and socket causing connection issues. The solution was to remove them and reinsert them which scrapes off the oxide.

I think for an experiment today, we'll try reseating the parts to see if that helps channel 6, if not then swapping them from channel 5 is a great idea. The other channels aren't perfect either, but they are much better than channel 1 and 3 so if the problem moves to channel 5 we know the culprit and I can buy new ones and install them.

Have you or anyone else watching this thread checked the tuning of their own functional Polaris to see how linear it actually is? I'm curious to know if the other channels going flat on low C is typical or atypical.

Thanks again. I'll post results after we test.