It’s worth prefacing this for background by saying that since I adopted the pinball hobby - er, habit - over 5 years ago, I’ve gleefully plunged into board work. Becoming intimate with thousands of components, and learning thanks to helpful friends here, I've successfully rebuilt boards on over a dozen games from System 6 through 11 (including complete overhauls on full boardsets), and even socketing WPC memory. That’s hundreds of capacitors, ICs, transistors, and other components... easily thousands of solder connections. I went from someone who barely knew how to solder and what this bit or that component did, to someone who can look at a game and think “eh, board work needed = discount for me, I got this”. It’s an awesome feeling.

So let's cue the humble pie!

I picked up a Blackout a couple weeks ago needing the typical System 6 go-over: board recaps, a few transistors out, 40 pin replacement, etc. No biggie! I got the game playable and rebuilt the sound boards and connectors while waiting for an order of power supply caps to arrive. They arrived and I got to work. But the radial replacement for the 12000uf cap was *so small* in physical size, I kept questioning: Did I order the wrong one? No… the correct spec is on the invoice. Did they pack the wrong one? No, the cap itself is labeled properly. Did the factory screw up? Well in the unlikely event they did, I surely can’t be the first one discovering it?

So I tell my stupid brain to shut up and quit distracting me while I go about replacing all the other power supply caps as I’ve done dozens of times before.

Still, I’m so anxious that when I install the board, I leave the MPU connector unplugged. Cuz if something’s gonna happen, I don’t want to take out an expensive MPU / Driver. So I connect the transformer inputs, stand by the lockbar, and turn the game on: ooh nice hum, display pilots glow.... 1, 2, 3 seconds and counting with nothing amiss, cool! Guess that weirdly small radial 12000uf is OK after all, so lemme turn the game off (*click*) and now go ahead and get that CPU connector seated, yep I’ll just plug it in he- KAPOWWWWWW!!!!!

It was almost exactly like that Rick & Morty "And one screw turn... and two screw turns...." bit: The explosion was so unexpected, sudden, and @&^@*& LOUD, and the smoke so acrid, I was literally dazed into a stumble as cotton fuzz wafted around my face, yet I quickly snapped to the *OH SHIT SOMETHING BLEW UP QUICK TURN THE GAME OFF!* and flicked the switch (*click*)… except the game TURNED ON WTF? DUMBASS! TURN IT OFF! (*click*)

*breathes*

*looks at mess in head*

WTF just happened?!?!

I'm sure a few of you have guessed: Yep. I was so concerned with the weird cap, that I completely overlooked the fact that for the first time ever, I installed a (different!) cap backwards. All my double-triple checking on previous boards, all those thousands of connections I bragged about above, and I never once installed something backwards: not a cap, not an IC, not a transistor, not a plug. I’ve often heard about what happens but never experienced it until now.

So Lemme tell ya, when it comes to caps, folks aren’t exaggerating: Not only was the explosion extra loud with my face so precariously close, I found the casing *on the floor about 6 feet away*! My wife heard it upstairs as well. And the packing fuzz (and electro-slime) embedded itself everywhere. (Needless to say, I was lucky).

I’m still most shocked that the cap literally blew *after* the power was cut... I suppose had I been watching, I might have seen it swelling or give some sort of warning. By pure stupid fluke coincidence, I turned the game off before surging it completely off, BUT the damage was done and it let go a few seconds later, literally not exploding until I touched the CPU connector to the board. I was so daze-confused my instinct to turn the game off literally hadn’t caught up to the reality that the game already WAS off… so there I went turning it back ON to exacerbate the problem… ha ha ha??

Anyway… it’s age-old advice but everything you’ve heard is true: CHECK THOSE CAPS BEFORE YOU TURN THE GAME ON!

Epilogue: Thankfully the rubber seal on the cap remained attached to the board, thus presenting the only evidence that I had indeed connected it backwards (versus some other defect). I replaced the cap in the correct direction, and all is well with the game. My ego however has a newly appropriate bruise
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whthrs166 Egad! That sounds horrific... I'm sorry you had to go through that. Yes indeed I've been lucky. I even had backpressure from a PVC potato cannon AND a balky furnace element blast me in the face, cartoon-style... but I guess the glasses saved my pupils (eyebrows singed in both cases). Heh. I'm really as dumb as I look sometimes. But more to the point, you have my sympathies! Now I'm gonna be paranoid about PVC.

@Tomahawkjim Wow... I never would have suspected the main switch if it looked OK. I've bought a couple sketchy "disinfect before bringing in the house" projects and inspected, so I can see how that could go awry. Glad it contained itself! Excitement makes life worth living sometimes, right?

Well anyway I know my story posts go TL;DR in a hurry so thanks for commenting... I just like to share my foibles from time to time.