Your drive 4 is out (J1, pin5), and return 11 (J12, pin 7). Pretty sure you have pulled a wire somewhere along the line. Check the green drive wire that runs between all these switches..
drive (resized).PNG
And the tan return wires from these ones..
return (resized).PNG

See if you have 3V at J1, Pin5. Red probe on the pin, black on ground anywhere.

Well I'm pretty sure you're getting a strobing signal from there. The switch drive pulses between 0-4ish volts, so on average you get a percentage of that. On a scope it looks like this..
503C0CE5-8BF8-4A80-985C-619DC8DE6702 (resized).jpeg
In this range though, the difference between 2.65V and 3.1V(which is what I get on a working machine) is significant, so there could be a chip problem, but you would need a scope to be sure. The difference may be in our meters.

I'm not sure on all the ways a chip problem will manifest. I always thought if it was dead it was dead and you'd get nothing. That's how most things fail. I would think you wouldn't get a strobe signal at all.

You should probably check all your switch diodes as well. Occam's razor and all that..