Suzuki Omnichord OM-84 Repair - Diagnosis Tips & Dunce Moment

Got my 1984 Omnichord back from the studio to do some work on a project and... it broke down. I fixed the first fault, caused another, wasted almost a month on the fault I'd caused like a total berk, but but did get it going again. This might be of use to anyone looking to diagnose a faulty Omnichord, as I cover a few pointers here, and in fairness I didn't hide my dumb mistakes.

Note: a couple of minor corrections:

Early on I mention the amplifier being on the smaller circuit board. Doh. The amplifier is on the main (big) board, not the smaller switchboard!

The 2007 date on the new amp chip is dubious. The chip sheds black stains when given the acetone-on-a-swab test. I think it's been sourced from China and while it works, I think it's been recycled, re-surfaced, laser etched and dressed up. Not an uncommon practice nowadays but this can reveal fakes or duds. It's frustrating. I could've put the old chip back in but didn't want to stress the pads on the board further. I will keep that chip though.

The hex inverter chip for the master oscillator is legit though.