Just an update in case anyone else is researching later on....
IC 20 was stuffed (and gate device, gates stuck on, read high on output pins when not called for)
also, it had taken out U28, the 74LS374 before it, couldn't test U20 till I changed U28
Also of note, when I tested the 7408 with a DMM, it tested OK. Pays to use logic probe as well once the board is powered on the bench.
