Earlier this year I restored a Firepower from cab to playfield to boards, and it was an incredible experience. After getting it debugged and paying my dues, it played solid for several months. It rested while we moved and did some other stuff, but since I've taken to playing it again it's started crashing with a short in the switch columns.
It did this when I first fixed it, occasionally... usually after a couple hours and dozens of games. But now, it seems to happen within just a few minutes.
What happens is during the middle of a game it suddenly tilts. Troubleshooting after this happens, you can generally press any Column 4 switch (which has all the pops, the "F" rollover, a couple other standups) and the corresponding Column 1 switches (coins, credits, tilts) will fire. But interestingly, the "4" "5" "6" and "Center Power" targets will fire on the "F" rollover. So it's not an exclusive "This column to that one" deal.
Even so, you'd might think this would be a simple thing: something wrong with the "F" switch, or elsewhere in Column 4. Or with whatever switches register during the short. But not so fast:
In chasing this issue I have investigated every thing I can think of: all the diodes test fine. The switches work fine. The leads and wires are not touching anything they shouldn't be. I rebuilt the pop switches and replaced all the diodes on column 4. I'll find or "make myself see" a random (if seemingly unrelated) maybe questionable connection here or there. Every time I improve a connection... replace the suspect diodes... rebuild the switches... I think "THIS TIME" I've got it...
...but I clearly don't. Because the kicker is, when the short happens it blows the 74HCT9114 on my Rottendog board. So in order to test and see if I fixed anything, I have to replace that chip and see if I'm OK.
Well, every time, the game works fine for a while until it doesn't. I can abuse it with the glass off in full multiball riot mode on the playfield and all will be fine... then a boring slow plunge hits a pop and POW. There's nothing to indicate any consistent fault state. No warning signs, no predictability. It doesn't even seem thermal since sometimes the game plays for 20 minutes or more and other times, not even 5. (And yes, I've made sure I'm not "tilting" the game somehow, to rule out that column as the source of the problem).
So yeah. In chasing this I've gone through my stash of those 74HCT9114 chips, partly during a party just to keep the game active. But now I'm down to my last...
...and K's Arcade is now out of stock. The part is obsolete. It's not available anywhere reputably close!
So this one remaining ship from my stash is literally my LAST shot.
WHAT should I be looking for? And how?
If this last chip blows, I'm screwed!