This looks long but please bear with me because I’ve diagnosed and fixed my share of WMS Sys 6 - 11 board issues, often without posting here, but I’ve got a weird one that’s frustrating me. Worse yet, it seems to be risking collateral damage and I’m nearly out of both parts on hand and ideas for the moment. Hoping for some insight to get me back on track.
Patient is my Time Fantasy UV conversion, freshly back from Pincinnati, its fourth show. It has the barakandl Special Solenoid Saver board installed, which I know works since TF has a geometry quirk where the ball occasionally gets “captured” between the right pop and the right wall rubber - it may oscillate in there “forever” and if pop bumper has enough, sure enough the fuse pops as desired before worse happens. To save fuses during “unattended play” at shows, I installed a 2A breaker there. And it works great: breaker pops before the transistor, reset that, try tweaking the pf level or whatever, and go on for several hours or more before the next occurrence. Point is: the protection circuit works as desired. Never had any other issues with this game.
Which makes this new scenario all the more baffling!
SCENARIO
At Pinci setup last Thursday, after a few hours (with sporadic set-up crew play) the lower pop went dead. Opened the head and the fuse for that pop had blown; replaced it and it blew immediately. Crap, that means the transistor right? Coil mech seemed fine but looked like the trigger switch got jammed somehow... ah, we have an explanation. So I adjusted the switch, replaced the TIP 102 and predriver, and was back in business. Cool! 'Cept I’m still a bit concerned the transistor blew WITH the fuse in this case: what gives? The fuse was only 1.25 A, it should have blown before the transistor could. But there’s no time to dwell on this at a show when I'm helping other people too... so I installed a 1.5A breaker in the fuse location for insurance.
Friday and Saturday played thru with no issues*. I personally play the game every hour or so to make sure it’s fine, and it was. Never even had to reset the quirky-troublesome right pop breaker either, go figure! *(technically there were a couple incidents owing to a rocket drain that mangled the outhole switch and caused some grief but I don't think that's related here).
Sunday was a short 4-hour show. Things were fine in the morning but an hour before close I realized the lower pop was dead again. Crap, but may as well wait and deal with it at home. Sure enough while breaking the game down to go home I see that yes, the breaker tripped, so there must be a deeper issue.
At home I discover the lower pop skirt is catching the edge of the playfield protector; I guess the protector shifted or something after all these years and moves. OK, that would certainly explain a pop getting locked on but the coil isn’t burned up too bad (wrapper is browned, but the plunger moves free), so yay for the fuse/breaker circuit! But after fixing the protector / skirt issue, and resetting the breaker, the transistor is dead again. Crap, again? If maybe not surprising…?
….But unfortunately, what IS surprising now is that every new replacement transistor (Tip102) blows IMMEDIATELY as soon as the pop bumper is triggered. No two-day's grace here. And the associated bumper fuse/breaker blows. AND the solenoid fuse on the power supply blows! This is not a slow-burn, 2-second time-bomb hear-it-buzz-can-you-react-first blow, it’s INSTANT. And also apparently new, because this didn’t happen Thursday!
TROUBLESHOOTING
-- At least I have a 2.5A breaker to put in the power supply for troubleshooting, and good thing too: Because under this blown condition, if I reset the breakers and turn the game on, they pop INSTANTLY even before attract mode starts.
-- If I remove the fuse/breaker for the lower pop state, the game boots and is playable.
-- If I replace the transistor + prediver combo again, the game boots fine. The components test fine in the board. No shorts on the board, which is really generally clean and nice. I can start and play a game. But as soon as I touch the affected pop bumper, POW. Everything dies.
-- I replaced the coil and diode with brand new: no help (and after removing the old I discovered that yikes, it was maybe more scorched than it looked).
-- I replaced the upstream driver IC8 with a 74LS02 (all I hand handy): no help.
IN SUMMARY:
the power supply fuse blowing instantly (AND the bumper fuse on this pop doesn’t work quick enough before) its transistor blows, is unlike any other symptom case I’ve dealt with. Obviously there has to be another short somewhere but I’m not seeing it, nor sure where to start. The wiring presumably should be fine. The connectors are good. The pop switch isn’t stuck because with new parts, the failure doesn’t happen until I close it.
It seems there’s something upstream that bypasses a “stuck coil burn in” and just kills the Q instantly instead, then runs with it all the way back to the PS and kills that too.
Could there be a short in the switch matrix somewhere, as previous collateral damage? Some other kind of wiring short to look for? Bad PIA to try diagnosing? I’ve not yet had time to pursue those ideas but before I head on a wild electron chase I thought I’d see if the hivemind had any ideas to narrow the field…
I installed the coil in the mech, note how that one points the lugs and diode AWAY from you... then resoldered the wires in their original locations. You'll note the other two coils have the double-wire on the doide's banded side. If this new diode is backwards... well crap, of course that's bad, and I wish I'd caught that yesterday.
Because of that I stepped back down to a 122 as originally spec'd in the manual, that actually caught on fire 
Maybe I can try another 122 and see if it... doesn't... catch on fire...?
