(Topic ID: 327010)

Game died after 4th show :( WMS sys7 transistor and fuses blow INSTANTLY

By goingincirclez

1 year ago



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  • 10 posts
  • 6 Pinsiders participating
  • Latest reply 1 year ago by zacaj
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#1 1 year ago

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…

#2 1 year ago

If the coil was heated up, it may have an internal short, or the diode on the coil may have shorted out. Disconnect the diode, and the power lead to the coil, and check the coil resistance, and the diode function. I seem to recall that just about every coil in early williams solid states are 23-850s, which should have about 5 ohms of resistance. If the coil is shorted out, as soon as it is fired, it will take out the drive transistor.

You can find the resistance for your coil here: https://flippers.com/coil-resistance.html

#3 1 year ago

Usually I'd think this is a bad diode, or other dead short, to blow it so fast. You replaced the diode and coil, are you sure you hooked it up correctly the second time? Check the resistance from the coil voltage line to the driver board pin / non-banded side of the diode, make sure it equals the coil resistance. Try firing the solenoid with the coil itself disconnected from the 34V line. Could be some other short has been introduced

#4 1 year ago
Quoted from goingincirclez:

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,

I thought that was just certain ones but I guess it's all of them.

I don't think circuit breakers pop as fast as fuses do, so you might want to use a lower value (1a?) instead in this situation. I had a laser cue where the drop reset coils would lock on occasionally, and the main solenoid fuse wouldn't blow, it just cooked the coil.

As for the core issue, if there are passives around the circuit, replace those as well or at least test. I'd test with the connectors removed to the special solenoids (input/output) and a logic probe so you don't blow anything (or it shouldn't, anyway) - compare other specials input/output to your problem one. You can ground the input to simulate what the game does.

Easy test to see if you've got a ground at the input on the connector, that might be the problem.... might have to trace the wire all the way down. Also, the activation switch, maybe replace the RC network there?
You can cut one leg of the cap on the switch off to test, the resistor and cap are only there to provide a minimum pulse.

#5 1 year ago

I think this is already mentioned but I’d disconnect the connector at the driver board powering the coil that causes the game to die when the pop bumper switch is made. Thinking along the lines of isolating the root issue from the board versus anything downstream to the coil. If after closing the pop bumper switch still results in a tripped circuit breaker (or blown fuse), I’d think it would have to be a short on the driver board or bad components. Btw, I had a bad TIP122 once after installing it. The replacement TIP122 blew right away (original was TIP122 that had failed); I switched over to TIP102 and it was fine. Point being the 122 should have worked but still was dead. I had 102’s around so put that in but I think I just had a junky supply of 122’s. Maybe you have some bad replacement parts?

#6 1 year ago

Finally home from surgery but still a bit groggy... but glad to see some hints thrown my way, thanks gents!

Quoted from uncivil_engineer:

If the coil was heated up, it may have an internal short, or the diode on the coil may have shorted out... should have about 5 ohms of resistance. If the coil is shorted out, as soon as it is fired, it will take out the drive transistor.
You can find the resistance for your coil here: https://flippers.com/coil-resistance.html

That's where I was last night when I replaced the coil. They tend to read bad with blown tansistors but even after disconnecting the diode, then the coil, it was still way off compared to the other two. I don't recall what it read, other than it was obviously wrong. So I put a brand-new unused coil in, it read properly, yet here we still are... but I'll come back to this in a bit. BTW I never saw that link before, looks handy. Thank you!

Quoted from zacaj:

You replaced the diode and coil, are you sure you hooked it up correctly the second time? Check the resistance from the coil voltage line to the driver board pin / non-banded side of the diode, make sure it equals the coil resistance. Try firing the solenoid with the coil itself disconnected from the 34V line.

Was going to try that, but stay tuned...

Quoted from slochar:

I don't think circuit breakers pop as fast as fuses do, so you might want to use a lower value (1a?) instead in this situation.

I'd heard that and it's valuable to remember, but here's the funny thing: Andrew recommends 1.25A fuses in his solenoid saver board. On that capture-pop, I found that would blow often. So I stepped to a 2A breaker as previously discussed and that worked fine in this application: even if the breaker might finally trip on delay, the coil and transistor are solid. I've never had to touch either despite that geometry flaw firing the pop hundreds of times a minute now and then.

Quoted from slochar:

if there are passives around the circuit, replace those as well or at least test. I'd test with the connectors removed to the special solenoids (input/output) and a logic probe so you don't blow anything (or it shouldn't, anyway) - compare other specials input/output to your problem one. You can ground the input to simulate what the game does.
Easy test to see if you've got a ground at the input on the connector, that might be the problem.... might have to trace the wire all the way down. Also, the activation switch, maybe replace the RC network there?
You can cut one leg of the cap on the switch off to test, the resistor and cap are only there to provide a minimum pulse.

All good ideas, and I had a couple of them last night while sleeping restlessly. I did test the pullups on board and they were fine. Thought about switches and tracing the wire(s) but hadn't gotten there yet... but may... but read on.

~~~~

So anyway, I'm groggy from surgery and the doc said "for the rest of the day don't drive, attempt to work from home, or do anything that might cost you money" ha ha. But I had a thought about the diode/coil and went for another look. Here's what's installed right now:

20221206_144245 (resized).jpg20221206_144245 (resized).jpg

Hard to see in that lousy photo BUT it looks like the diode on this new yellow coil was installed BACKWARDS compared to the others, arrgh! I did not catch that! 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.

So obviously that needs to be fixed but the BIG question is: could that one backwards diode be causing the entire insta-fry issue now? Remember, it existed before I swapped the coil, but it seems that same old coil might have degraded-to-shot by then. So maybe it's possible and worth checking BUUUT I'm down to my last spare TIP102 on hand 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...?

(remember what that doc said...)

#7 1 year ago

A backwards diode will instantly blow any transistor attached to it the first time it tries to fire. And it'll usually ruin the diode too, so even if you replace the transistor and realize your issue and swap the coil wires, it can still have an issue.

Without knowing what the original coil read/etc it's hard to say what the root cause but the reverse coil wiring explains all the current issues

#8 1 year ago

Get this fixed yet? I forgot about the diode being backwards on some coils.

#9 1 year ago

Phew, this update is late (was 100% busy Wed, Thurs, yesterday, and all-today-til-now) but YES I did get it fixed.

And yes it was that *&@^U^&@ coil diode!

Which... chrissakes man, I was on that suspicion track all along, when the original coil seemed suspect I replaced the diode first (no change) and then the whole damn thing (no change) and in the long day and compounding frustrations didn't realize the diode on the new OEM coil was *backwards*... so of course there was no change still, leading to my confusions... fffffuuuu!

Still, this was a pretty illuminating exercise as to how the collapsing EMF plays havoc upstream, without a proper diode. I've had bad diodes before, but never one to cause this type of problem. Still a bit annoyed that the added solenoid fuse wasn't enough to prevent damage upstream BUT I'm glad it wasn't worse.

Anyway, I reversed the diode/wires and replaced the transistor - with a weaker/OEM TIP122 no less - and am back in business. No other damage, and having identified the tricky root cause being the pf protector shifting, I hope to be solid from here out.

Thanks all for the assist! I owe a few brews at the next show, some find me

#10 1 year ago

A broken open diode is very different from a shorted/backwards diode in terms of the issues it'll cause.

I'd also recommend you stop thinking about diodes being "backwards" on coils. There's no such thing (on single wound coils). The diode determines what forwards is, and assuming that coils will be facing the same way is just going to lead to more mistakes like this.

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