I think the power supply is definitely the culprit here- been doing some tests per the service manual and see that my 5v rail is draining. So by the time it drops to like 2-3 volts everything locks up. I made sure to test the power supply pins also with the connector off as it says to see if voltage exists there (pin 12 and 14) and I get nothing. So reading through the power supply notes it lists the potential culprit parts.
Knowing it's silly to repair without a recap I will be doing that as well.
The supply uses LM723N voltage regulators. Obsolete part. I found 1 in a pile of old ICs, but I don't know if it's good. Is there a way to test these (or any IC for that matter) with a scope out of circuit to see if it's working internally? I don't want to just start part-swapping with this synth, not at this caliber.


Also, it lists "P3" in the troubleshooting steps. I don't know what "P3" refers to. The connectors are P13x.