Newly built A4000 motherboard. Tested all resets, supply voltages, and there was video out. DiagROMs would also not initialize, indicating very early fault during boot (during reset routine). _OVL signal on CIA B (U350) would go to high at hw. reset, but would not return to low indicating the CPU didn’t write back to CIA registers to continue the boot process after chip RAM was tested.
Eventually found a manufacturing error on DATA lines (D5) KS ROM pin 24. The precision pin receptacle was wider than standard, causing ROM pin not to make contact. (see pictures)