I would hold off on CPU replacement - unless there is no E clock output (1 MHz).?
Focus on U45 - are you sure you have a 74LS02? Quad NOR gate part?
If you used a different part, e.g.? 74LS08 (Quad AND gate)? - that would explain U45A and
U45B operation - but not U45C - can't understand what is going on.
