We did some more testing and troubleshooting today but the situation is still pretty much the same unfortunately. Couldn’t find any continuity issues. Unfortunately we don’t have access to a scope, I’ll have to try and get one one day.
The Preset switches themselves seem to be fine, the selection LEDs are turning on/off when we’re pressing them. The problem does seem to be either in the switch memory section with the three IG00157 ICs, or the TC4016BP selector gate IC. Because the LEDs are changing as expected (only one at a time on the last pressed button), I’m wondering if the switch memory stuff is working correctly but it’s a fault on the IC4 (TC4016BP) chip, and the gates for Manual and Preset 1 aren’t working.
There’s also the external connection into that section from the Initial Clear circuit that could be messing with the switching logic, but I have a hard time figuring out if that would cause the symptoms and how to even check if there’s an issue with that stuff. The associated connectors all seem fine.
So I’m thinking we’ll try the bypass, my main concern and question now is if there’s any reason why pulling IC4 and just bridging pin holes 1+2 with an appropriate resistor might cause other problems? -
If we leave Organ 1/2/3 disconnected will that be fine? Or might there be some other consequence to the overall circuit if we do that?