Pin 15 U5 held low
Pin 12 Z26 held high

AFAIK the mod doesn't touch U5.  Pin 13 is the only one which buzzs out to where the mod is.....
Pin 40 on U1, with DMM 0.0 then jumps to around 4.5 to 4.8v and holds there.

Pin 40 should ALWAYS be 5V (or near enough) which means the cpu is NOT in reset, that's cool.

Re-Check :

Pin 15 U5 held low
Pin 12 Z26 held high.

The schematic shows they directly connect, if one is high so will the other, yet you see 2 different levels?

maybe a cracked track in between these 2 pins??