Thanx got the schematic, silly me 'selective reading' again, so i missed it hehehe

Umm, looking back at the start of post, although you have 'no displays at all' does the pin powerup or do anything? can u play a game, and flippers, bumpers, rollovers work and make sound etc??
(sorry if i missed this before).

I'm thinking maybe the master clock (Z3-7404 & Z2-7474 into U1-6502) might be dead? which would mean no bootup therefore no IRQ 'flash' that you expect to see.
The 'E2' link might be open?
Of course if the game runs, then ignore this, obviously the master clock is ok into the cpu...

Also, U1-6502, pin 39, which is a cpu clock signal going out to all PIA's, i'd be looking around there too, in & out of that Z3 etc....

The only bummer is you'll need a Cro or frequency display on your MM to measure the presence of the clock signal, capable of reading say 2-4Mhz ?? ??
You *might* be lucky that your logic probe has an inbuilt frequency-divider and will show a blinking pattern....try it i guess.

Also look at U5 pin34 (reset) and see what levle it is held at, maybe chip is held in a reset state??

I'd also look at U5 pin15 (Z26 pin12), and see what that signal is doing, it looks like the 'slam switch' does something to the score driver, blanking it? or something...if it's held in a state, maybe U5 is simply locked out, hence no IRQ??

Hope this helps.
MM.