Nova 2001 repair log #2

Another Nova 2001 repair log here after the one from Corrado.Here is the “patient” on the operating table today:

PCB was sent me flagged as “SOUND ERROR”, indeed when I fired it up, the music and sound FXs were only noises.Here is a record for a better understanding of what I mean:

All sound/FXs are generated by two AY-3-8910 chips so I went to probe them  and found no activity on all their pins.This was due a missing clock on PIN22 of both (signal is shared) as shown on analog scope:

I could trace the CLOCK signal back to PIN9 of a 7474 @3E and comparing the chip with a good reference one using with my HP10529A confirmed trouble on this output:

It failed miserably when tested out-of-circuit:

Mission accomplished, another arcade PCB preserved!