How driver board lamp latches work

Twelve 74175 quad latches (Z1-Z12) hold the lamp states. Four lamp data lines (LD1-LD4) go to all twelve chips, and each chip has its own data strobe (DS1-DS12); when a strobe pulses high the chip stores whatever is on LD1-LD4. Z12 uses both its true and inverted outputs so four pairs of lamps can be alternated.