I was so close a month ago… I should have stayed with it. Sustain was low whenever it sounded okay. Whenever sustain reached the halfway point the keyboard would make a horrible screeching sound. The only reason it seemed to work was that it powered up to a random patch where the sustain level was low.
I thought back to Sam’s videos in the Synth Wizards series: start at the oscillators and work your way through the signal flow. I found that my envelope was peaking at 7v when the specs say that the output of the CEM3310 will be from 5v maximum. Attack wasn’t looking right, either - instead of slowly rising, it snapped to sustain level after a delay. Replaced the chip with an AS3310 I had on-hand and it is working great. Probably presenting too much load on the +12v line as well. I couldn’t see much change in the filter section, either, so swapped out the CEM3320 for an AS3320 as well. That’s sounding good now too.
I’ll take another look at the #0/Norm switch - Probably a bad 4066. Then I just have to finish rebuilding the keybed and tune it up.