Super thanks for the online diagnosis. Based on your feedback I'm going to do this:
1) Pull the board, clean up, and test the surrounding traces
2) Replace the potentially fried chips via the rec'd approach with a socket vs. direct chip
3) Test and re-assemble.
While pulling this out I may also clean the key contacts as well as the knob contacts.
I've attached a couple photos verifying the corrosion that you mentioned as well as a spot where they repaired a broken circuit via a lead.
Thanks again - I'll post back updates here.
Best,
Adam
