God I hate these ‘one and done’ posters.
They ask for information and advice about their various projects and we offer advice, and hear absolutely nothing ever again.
I was very interested in hearing how this Moog Source restoration was progressing, but nada, zip. 
Not “done” yet, just had to walk away for a while…and for some reason I haven’t been getting notifications when others posted.
I have swapped around all but one IC on the synth board for good measure. Figured it was a long shot since it seems to be a digital issue, but it was quick and easy since they’re all socket mounted. Still no luck. So I’m back to the digital board, looking for something that’s causing it to hang up the address or data lines.
Also have a noise issue to contend with (oops), it also seems to be on the digital board, so I need to follow the audio signal circuit to see what’s unhappy there.
Going to replace the p/s caps…looks like one may be a little leaky (and I have them on hand), but the originals are still doing their job for now.
Probably spend a few late nights with the schematics and scope to see what turns up.
Strangely enough, I also bought a metal detector from the same guy. It also has a membrane switch issue…and happens to run a Z80 processor.
Any other pointers would be appreciated.
I’ll try to check the board more often and provide updates.