(Topic ID: 294552)

LOTR Blowing Transistor, Coil, Fuse... I'm stuck

By MaxAsh

3 years ago


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  • Latest reply 2 years ago by FlippyD
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#1 3 years ago

Hey All, hoping for a little help and a sanity check. I'm helping someone with their Lord of the Rings, and I've hit a snag. Before I go further, I wanted to see if someone could offer some advice.

History:
A while back he had a dead pop bumper and a stuck-on flasher. I did some testing, pulled his driver board, and found the associated transistors were bad. I know they're a little weak on this game, so it wasn't a huge surprise. Replaced the transistors, as well as the burned out pop coil, and he was good to go.

Fast forward a couple months and he texted saying his F21 kept blowing. He realized it happened every time the ball goes into the Orthanc VUK. I checked and the coil was toasted, coil sleeve partially melted. Pulled the board and the associated Q4 transistor was shorted.

Current Attempt (failure):
I replaced the Q4 transistor (using the recommended IRL540 'upgrade' over the original 20N10L), replaced the coil, and the fuse. The old coil looked like it had its diode snapped partially off, which may have been the problem.
I tested the new transistor and coil before and after install, seemed good. Fired the game up, but as soon as that coil was triggered the same thing happened: Fuse, Coil, and Transistor all blew.

So I'm at a loss for the moment. Normally a bad transistor / coil have been the culprit for me over the years with most games. Is this a possible chip issue? With 3 transistors and 2 coils getting killed in the past few months, could something be going? Could just be a coincidence. Thanks in advance for any advice/help. Not sure where to go next.

#2 3 years ago

Additional note, the old VUK coil diode was snapped off on one side. I assumed maybe that's why it blew originally.

The guy who owns this game loves it to the point of playing hundreds of games a month. It gets played all the time, so hopefully with some help I can get him up and running soon!

#3 3 years ago

If the diode was snapped off of the lug, I would def check to make sure it's not making contact with something and shorting out when the PF is closed. In theory something or someone broke that diode leg off.

#4 3 years ago
Quoted from MaxAsh:

Additional note, the old VUK coil diode was snapped off on one side. I assumed maybe that's why it blew originally.

A broken/ missing coil diode will cause the drive transistor to blow every time, maybe not on the first activation but likely within 3.

Quoted from MaxAsh:

I replaced the Q4 transistor (using the recommended IRL540 'upgrade' over the original 20N10L), replaced the coil, and the fuse. The old coil looked like it had its diode snapped partially off, which may have been the problem.
I tested the new transistor and coil before and after install, seemed good. Fired the game up, but as soon as that coil was triggered the same thing happened: Fuse, Coil, and Transistor all blew.

Coils don't generally "blow" but fuses, diodes, and transistors sure do.

Coils with diodes MUST be wired properly, if the power wire is not connected to the same coil lug as the striped side of the diode (cathode) then the diode will be forward biased all the time and the instant you provide the return path for this power to flow (provided by the transistor the first time its commanded on) the diode will essentially act as a dead short and allow as much current as you can provide to flow through it and immediately destroys both the diode and drive transistor....which then blows the fuse.

The fix: replace the coil diode, drive transistor, and fuse all at the same time; the coil will be fine as zero current has flowed through it in this scenario. Verify the coil voltage wire is connected to the proper side of the diode and you should be good to go. I would also measure your coil resistance (with the diode removed just to be sure).

#5 3 years ago

Here's what I found when I pulled the original melted coil.

I actually did replace the coil, transistor, and fuse all at the same time. I tested the coil resistance before installing it, and it was in the low double digits (I forget the exact number at the moment, but 10-12 ohm range I think). The fried one was 1.5 ohms.

I'll double check the wiring to make sure I didn't install it backwards.

PXL_20210603_221827568 (resized).jpgPXL_20210603_221827568 (resized).jpg
#6 3 years ago

Did you test R4 when you replaced Q4? Drive transistors always have other components like resistors, diodes and capacitors in the same circuit. Those components can be taken out when the transistor is taken out. Usually you can test those components in circuit (after shorted transistor is replaced) and compare them to neighboring similar known working components.

Q4 doesn't have any diodes in the circuit (there's one on the coil), but R4 definitely needs to be tested. If R4 tests good, you may have a problem upstream of Q4. That's usually about the time I call Rob Anthony.

#7 3 years ago
Screenshot_20210604-181902 (resized).pngScreenshot_20210604-181902 (resized).png
#8 3 years ago
Quoted from phishrace:

Q4 doesn't have any diodes in the circuit (there's one on the coil), but R4 definitely needs to be tested. If R4 tests good, you may have a problem upstream of Q4. That's usually about the time I call Rob Anthony.

I would have to disagree with this as this single statement from the OP tells me there were no control issues with this board and that Q4 was operating perfectly until it was taken out on activation:

Quoted from MaxAsh:

I tested the new transistor and coil before and after install, seemed good. Fired the game up, but as soon as that coil was triggered the same thing happened: Fuse, Coil, and Transistor all blew.

#9 3 years ago

The Capacitor next (C267) to Q4 tests shorted at the moment. I noticed the same thing when the previous transistor was blown/shorted. As soon as I replaced the shorted transistor, the capacitor was fine, which makes sense. I did not fully test the resistor (it was not shorted though, I did check that).

Waiting for the guy to take a pic of the coil to verify the wiring.

#10 3 years ago

Just got the pic of the coil from him, and it makes sense now. Diode was reversed on the replacement coil. I missed that detail, and wired it backwards it seems. Boom.

Thankfully, I have a spare coil, transistor, and plenty of fuses. I don't think anything else would be blown, right?

#11 3 years ago
Quoted from MaxAsh:

Thankfully, I have a spare coil, transistor, and plenty of fuses. I don't think anything else would be blown, right?

I give you a 100% guarantee that the diode is a now a dead short and will need to be replaced. You also won't have to replace the coil as no current passed through it, all current flowed through the diode as it as the circuit would have seen it as a solid wire essentially bypassing your new coil.

I doubt anyone here cares about details on PN junctions and depletion regions so I wont explain why your diode failed.

#12 3 years ago
Quoted from Pin_Guy:

I would have to disagree with this as this single statement from the OP tells me there were no control issues with this board and that Q4 was operating perfectly until it was taken out on activation:

Ironically, I was looking at the board because of exactly what you quoted from the OP. He said he tested the new coil before powering up. He said he successfully replaced a transistor previously, so I assumed he knew to watch polarity on the coil.

There are lots of things I always double check before applying power. Diode orientation on a new coil is high on that list. Stern's are a little easier as the ground wire is usually a smaller gauge wire than the power wire.

#13 3 years ago

Yeah, I usually double-check, triple-check, and take pics. In this case I did the worst thing you could do: got all excited all the harder work was done, and rushed the final step.

Got back a bit ago. Everything is up and running well, and playing great. Didn't take long to pull the board, install the new transistor (again), and replace the coil (properly). He's thrilled to be flipping again. He easily puts hundreds of games on it a month, so I'm sure I'll get another call soon. He doesn't want to go LED all over, but he let me throw some warm whites in his lower GI, looks much better. A lot of bulbs were out too, ones he didn't notice, so the game looks a lot better.

I just need to convince him to start shopping it more. It needs new rubbers, a tear down and shop, etc. But that's for another time.

Thank you all! I appreciate the help. And Pin_Guy I don't mind hearing the explanation, I fill my brain with all sorts of info like that, it's fun.

Marking solved, much appreciated!

#14 3 years ago

Nice work. When I power up after replacing a drive transistor, I watch the fuse for that circuit, the coil the transistor drives and I listen for any coils firing. I switch the game off quickly if anything looks or sounds wrong, hopefully before the fuse blows or the new transistor shorts. If you take it slow and don't taunt the repair gods, they usually cut you a break.

Tell your friend about the Pinball Life 'special' flipper coils, if it doesn't already have them. Makes the game way more fun. You can jack it up to 7 degrees and make the ring shot all day.

https://www.pinballlife.com/lotr-special-flipper-coil-090-5020-2ot.html

#15 3 years ago
Quoted from phishrace:

Nice work. When I power up after replacing a drive transistor, I watch the fuse for that circuit, the coil the transistor drives and I listen for any coils firing. I switch the game off quickly if anything looks or sounds wrong, hopefully before the fuse blows or the new transistor shorts. If you take it slow and don't taunt the repair gods, they usually cut you a break.
Tell your friend about the Pinball Life 'special' flipper coils, if it doesn't already have them. Makes the game way more fun. You can jack it up to 7 degrees and make the ring shot all day.
https://www.pinballlife.com/lotr-special-flipper-coil-090-5020-2ot.html

Great that you power up cautiously but the fuse will go open circuit (blow) LONG after any semiconductor shorts.

Fuses are mechanical devices and semiconductors will short (with excessive load) virtually instantly before the fuse has any chance of opening.

A common misunderstanding is that fuses are there to protect your equipment - nope - they are there to prevent the device from catching fire and burning your house down. Fuses won't stop semiconductor devices from shorting.

#16 3 years ago
Quoted from pins4u:

More
Great that you power up cautiously but the fuse will go open circuit (blow) LONG after any semiconductor shorts.

That 5 amp slow blow fuse is going to start glowing before it blows. That's what I'm watching for. Powering off quickly before the fuse blows saves the fuse, the transistor, the coil and the diode. Takes literally a second to see or hear if there's going to be a problem.

Do you have a different power up procedure after replacing a transistor?

#17 3 years ago

https://www.circuitbread.com/tutorials/how-does-a-diode-work-part-1-the-pn-junction

Quoted from phishrace:

That 5 amp slow blow fuse is going to start glowing before it blows. That's what I'm watching for. Powering off quickly before the fuse blows saves the fuse, the transistor, the coil and the diode.

In the OPs case nothing would have saved the diode or transistor, his coil never fired and both the diode and transistor were destroyed the instant the drive transistor turned on, then the fuse went after the damage was done. He may have seen it glow and could have turned off the machine to save the fuse, but any fuse that glows red is going to get heat fatigued and should just be replaced anyway.

#18 3 years ago

Yeah, they blew pretty much instantly as soon as the switch for that coil was triggered. I saw the fuse go bright and pop, and knew I likely goofed something up (or that something else was wrong).

So Pin_Guy you're saying that coil is still probably good, and I can just swap the diode?

phishrace I'll suggest the flipper coil swap, though he seems happy with the game as-is. Always good to have options!

Sidenote: I noticed his spinner doesn't seem to register much of anything points-wise. Been a while since I played LOTR, I assume that it should always score something, regardless of mode? I spun it when no mode was active and it didn't do anything. Thinking the switch might be bad? Just figured since you guys were here, I'd ask.

#19 3 years ago
Quoted from Pin_Guy:In the OPs case nothing would have saved the diode or transistor, his coil never fired and both the diode and transistor were destroyed the instant the drive transistor turned on, then the fuse went after the damage was done. He may have seen it glow and could have turned off the machine to save the fuse, but any fuse that glows red is going to get heat fatigued and should just be replaced anyway.

You didn't answer my question.

Powering off a game quickly will absolutely save parts. If you disagree with that, I'm not sure what to tell you. I said a second is all it takes above, but really it takes less time that. A five amp slow blow fuse will survive a brief glow just fine.

#20 3 years ago
Quoted from MaxAsh:

So Pin_Guy you're saying that coil is still probably good, and I can just swap the diode?

Yes.

Quoted from MaxAsh:

Sidenote: I noticed his spinner doesn't seem to register much of anything points-wise. Been a while since I played LOTR, I assume that it should always score something, regardless of mode? I spun it when no mode was active and it didn't do anything. Thinking the switch might be bad? Just figured since you guys were here, I'd ask.

You can verify it in Portals switch test; its probably a bad switch but could be a broken wire.

pasted_image (resized).pngpasted_image (resized).png
#21 3 years ago
Quoted from phishrace:

Powering off a game quickly will absolutely save parts. If you disagree with that, I'm not sure what to tell you.

You are missing the point and if you don't understand this I cannot help you.

Quoted from Pin_Guy:

In the OPs case nothing would have saved the diode or transistor, his coil never fired and both the diode and transistor were destroyed the instant the drive transistor turned on

The fuse will glow AFTER the diode and transistor blow, these parts were destroyed immediately at switch activation as in a thousandth of a second at the most; the fuse will not glow until after these parts failed because if they didn't fail, the fuse would neither glow nor blow.

Was this a question for me?

Quoted from phishrace:

Do you have a different power up procedure after replacing a transistor?

I toss the board in and turn on the machine, the transistor was already verified functional on my workbench; and I wouldn't remove the board if the transistors failure wasn't already determined prior to pulling the board.

If I wanted to be extra careful I would leave the coin door open to disable high voltage and take a resistance measurement between the transistors tab and ground. If there is low resistance here the transistor is "ON"

#22 3 years ago
Quoted from Pin_Guy:

Was this a question for me?

Yes, both times I quoted you. It's painfully obvious you have a chip on your shoulder against me from that previous thread. That's very telling to me on a number of levels. It's obvious we aren't getting anywhere here, but thanks for helping others, anyway.

#23 3 years ago
Quoted from phishrace:

You didn't answer my question.
Powering off a game quickly will absolutely save parts. If you disagree with that, I'm not sure what to tell you. I said a second is all it takes above, but really it takes less time that. A five amp slow blow fuse will survive a brief glow just fine.

You obviously have no technical training in this field. No matter how fast you switch off, the damage to semiconductors happens in milliseconds - no time for you or the fuse to react. It doesn't really matter what you believe, semiconductors will short or otherwise be damaged regardless.

I suggest you do some research on how semiconductors work before misleading people (speaking with my electronic engineer hat on).

You may well be able to reuse a fatigued fuse but its performance will be seriously degraded.

#24 3 years ago
Quoted from pins4u:

You may well be able to reuse a fatigued fuse but its performance will be seriously degraded.

Yep, and it will likely blow at some point for no reason and ruin your game ... probably right as you make that last shot needed to start Valinor.

#25 3 years ago
Quoted from pins4u:

No matter how fast you switch off, the damage to semiconductors happens in milliseconds - no time for you or the fuse to react. It doesn't really matter what you believe, semiconductors will short or otherwise be damaged regardless.

Read what I posted again. I didn't say that killing power quickly would save parts in this specific case. Just a general procedure I follow after replacing transistors or if I suspect a transistor might be already shorted. I find incorrectly installed diodes on switches often enough, but pretty rare to find a coil diode reversed.

Between operating pins on location and running my own pin repair business, I've fixed thousands of games over the years. I claimed my repair business on Yelp when I started it and I've only gotten 5 star reviews. I won't claim to be the best tech ever, but I've done warranty calls for both Stern and CGC, so apparently someone thinks I have a clue. Do either of you guys fix pins for a living?

I've also been helping people here and on RGP for more than 25 years. That's not going to stop. And yes, I did go to school to learn my trade.

1 month later
#26 2 years ago

In a similar boat to this thread - my right flipper died mid game multiball. Never locked up or anything. I confirmed the diode was toast but the coil still has a normal resistance once I removed the diode. Based on this thread it sounds like just replacing the diode is not going to help me, the transistor is 100% toast as well and needs to be replaced in tandem with the diode? Or is there a chance I just replace the diode and the transistor is still good?

I did try replacing the fuse before I knew the diode was toast and it died.

Update also just tested Q16 and i get continuity (buzz) when testing the backplate to ground, while Q15 (good flipper) doesn't buzz... so it's gotta be the transistor as well at this point.

Thanks

#27 2 years ago
Quoted from Junglist:

In a similar boat to this thread - my right flipper died mid game multiball. Never locked up or anything. I confirmed the diode was toast but the coil still has a normal resistance once I removed the diode. Based on this thread it sounds like just replacing the diode is not going to help me, the transistor is 100% toast as well and needs to be replaced in tandem with the diode? Or is there a chance I just replace the diode and the transistor is still good?
Thanks

Hey saw you in the LOTR thread. It definitely sounds like you need to do the transistor. If you don't want to do it yourself and you don't know anyone local to do it there are several reputable people that fix boards. Rob Anthony is first one that pops in my head. Someone like that could even bulletproof the board with all upgraded transistors, new caps, etc.

Dig in here if you are inclined to go the DIY route or want further info on how to diagnose this issue: https://homepinballrepair.com/understanding-pinball-ss-transistors-diodes-rectifiers/

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