Quoted from JBee:

Hey guys, I am really really interested in buying a BH. Was 11 in '81 and remember this fondly from the arcade. Am I insane? The more I read about this pin the more scared I get. I'm very handy but not an electronics expert. (repaired an EM Gulfstream myself) I also remember this pin being 'out of order' at my local arcade half the time

Quoted from goingincirclez:

Yay, turns out it was just the Z21 7448 after all! Replaced it and all displays work just like they should with no other repairs needed (Looks like one of those displays also has a busted filament wire but I'll move that to P4, and it's at least functional otherwise).
Have to say that little $20 40- and 74-series logic chip tester I got off ebay just paid for itself: I didn't expect to get a bad batch of 7448's, but glad to confirm, otherwise there's no telling how long I'd have been frustrated here!