(Topic ID: 119804)

[SOLVED] Stern IM: Why both flipper transistors shorting?

By onetaste

9 years ago


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#1 9 years ago

I've just taken possession of a HUO Iron Man classic. It travelled over 3,000km to get here. After half an hour of play the Right Flipper fuse blew. It blew again immediately after power on, so I found a shorted transistor on the driver board (diode was OK). I replaced the transistor and right flipper works fine now.

However, after a further 1 hour of play exactly the same thing happened to the left flipper. This has me worried. Before I replace the transistor for the left flipper I thought I better check with the experts whether there may be something somewhere else in the circuit causing this problem. Any suggestions?

Thanks, onetaste

#2 9 years ago

Its pretty common on sterns for the flipper transistors to blow. Especially if you hold the flipper button too long. Happened to me a few times. make sure the correct transistor is in there as it may have been replaced before. I would also double check the coils and wiring. Never know what has been hacked up on a pre owned pin.

#3 9 years ago

Yeah, you're absolutely right, vintage4life, I was in multiball both times holding a second ball on the flipper. So it was holding the flipper that stuffed the transistors.

What is the solution to this problem? Put in a transistor that can handle higher amperage? Obviously there is a solution for this, since these machines are used in PAPA comps and the flippers don't blow there.

I am running the latest code update for Iron Man.

#4 9 years ago

I must say that is pretty sad for this to be happening now, on newer machines. I thought that most issues like that would have been worked out with better engineering.

#5 9 years ago

OK, found the answer, upgrade the mosfet transistor to P40NF10L or next best IRL540N.

#6 9 years ago
Quoted from onetaste:

OK, found the answer, upgrade the mosfet transistor to P40NF10L or next best IRL540N.

That was my solution -- but it still leaves you vulnerable. Perhaps it will take a longer hold period, for example, but it will happen again if you aggressively trap in multiball. I ordered some heat sinks from Great Plains Electronics, and I hope that the new transistors coupled with some heat sinks to dissipate heat will prevent the transistors from overheating and failing.

The Stern flipper design is to pump full power through the transistor to fire, and then pulse the current to hold the flipper up once it has fired. But after several minutes, even the pulses seem to be overheating the transistors.

A few posts from my travails here: https://pinside.com/pinball/forum/topic/acdc-flipper-problem-coil-stuck-on

Good luck!

#7 9 years ago

I just replaced the same transistors for a friend on his LOTR.Both were shorted and I put the IRL540N's in.
We will see how they work out in time.

#8 9 years ago

Thanks for your help, guys. I trap the ball for long periods during multiball. If this doesn't solve it I'll let you know.

#9 9 years ago

Oddly enough I recently had a recurring issue with a Nascar doing this. After the 2nd time I replaced the predriver IC 74hct373? just going off memory. Problem solved. It seemed this ic was marginal causing an issue as well. So now when I replace a bad flipper trans I socket and replace the ic as well.

4 weeks later
#10 9 years ago
Quoted from onetaste:

OK, found the answer, upgrade the mosfet transistor to P40NF10L or next best IRL540N.

Update: Stern support suggested the P40, which is a 40 Amp mosfet, but they were the 2 originals that blew. Someone here in Australia advised that the IRL540N caused him other problems on the circuit board. So I put in a new P40NF10L and attached heat sinks to each of the flipper mosfets and I've had no problems since.

#11 9 years ago

IRF540 is rated for 28A continuous or 110A pulse, if you are blowing these quickly I would make absolutely sure those diodes are actually good

#12 9 years ago
Quoted from onetaste:

Someone here in Australia advised that the IRL540N caused him other problems on the circuit board.

Do you know what those problems were? I have had the P40's blow in a couple of games, and I've replaced them with IRL540 with no further issues. I'm curious about what problems he saw, though.

#13 9 years ago
Quoted from flecom:

IRF540 is rated for 28A continuous or 110A pulse, if you are blowing these quickly I would make absolutely sure those diodes are actually good

I think you want the L version for logic level. F is something else and may pulse differently and cause early failure.

#14 9 years ago

Remove caps C52 and C53 from IP board.

#15 9 years ago
Quoted from Eddie:

Remove caps C52 and C53 from IP board.

What does that do? Change the pulse width?

#16 9 years ago
Quoted from barakandl:

I think you want the L version for logic level. F is something else and may pulse differently and cause early failure.

I missed the IRL part, I always use IRF540s without issue, haven't replaced one twice yet

#17 9 years ago
Quoted from barakandl:

What does that do? Change the pulse width?

I'm curious about this as well. I found another reference to it in the "what failed today" thread, but I couldn't find the reasoning.
https://pinside.com/pinball/forum/topic/what-failed-today-modern-pinball-machine-fails/page/4#post-2009676

#18 9 years ago

The schematic I have of the SAM IO board doesn't show a C52 or C53.

#19 9 years ago

IRF Gate threshold is 2v to 4v.
IRL Gate threshold is 1v to 2v.

IRL is the TTL part which is what the circuit calls for. While the IRF part may work fine, it also may cause problems with not fulling turning on. Pulse width could change too, but i am little shaky on the actual theory.

Andrew

#20 9 years ago

I've seen IRF MOSFETs cause problems on Stern flippers. They don't fully turn on when the hold voltage is being pulsed to hold up the flipper. A slight hit from a ball makes the flipper drop and high power to be reapplied. It gets annoying as the flippers drop and then pulse back up. Best to go with logic level (IRL).

#21 9 years ago

LOTR has had no further issues with IRL540 replacements so far.It's been about a month and the pin has had some heavy play at times.

#22 9 years ago
Quoted from barakandl:

IRF Gate threshold is 2v to 4v.
IRL Gate threshold is 1v to 2v.
IRL is the TTL part which is what the circuit calls for. While the IRF part may work fine, it also may cause problems with not fulling turning on. Pulse width could change too, but i am little shaky on the actual theory.
Andrew

last I checked they are being driven by 74 series logic so output should be about 5v or more than enough to drive either part

#23 9 years ago
Quoted from flecom:

last I checked they are being driven by 74 series logic so output should be about 5v or more than enough to drive either part

They are, but not directly. There is a 22k resistor between the driver and the gate.

#24 9 years ago

considering an IRF540 is rated to draw 22uA I think the voltage drop across a 22k resistor is negligible

#25 9 years ago

In steady state, yes, it is negligible. When switching, however, the resistor will slow the transitions, and the higher gate threshold can cause problems at certain switching speeds. I really don't know if that's the case here.

#26 9 years ago

are you sure you are not thinking of inductors?

resistors do not do what you are describing

#27 9 years ago
Quoted from herg:

The schematic I have of the SAM IO board doesn't show a C52 or C53.

1.jpg1.jpg

My final info on this issue.

#28 9 years ago
Quoted from flecom:

are you sure you are not thinking of inductors?
resistors do not do what you are describing

I really didn't mean to start an argument, but yes, a series gate resistor does affect the switching speed of MOSFETS.
http://www.edaboard.com/thread139630.html

Whether or not it makes any difference in this case, I don't know.

Quoted from Eddie:

My final info on this issue.

Hmmm... Those same capacitors are C248 and C247 on my schematic.

#29 9 years ago
Quoted from herg:

I really didn't mean to start an argument, but yes, a series gate resistor does affect the switching speed of MOSFETS.
http://www.edaboard.com/thread139630.html
Whether or not it makes any difference in this case, I don't know.

Hmmm... Those same capacitors are C248 and C247 on my schematic.

the circuit in that thread requires two fets, the first has a resistor from the input logic level to ground to slowly bring up the second fet (vs the sam board that just as a resistor in line to the fet)

2 weeks later
#30 9 years ago
Quoted from herg:

Do you know what those problems were? I have had the P40's blow in a couple of games, and I've replaced them with IRL540 with no further issues. I'm curious about what problems he saw, though.

He said it caused problems further upstream with capacitors. That's why he recommends replacing the mosfets with the P40s and attach heat sinks.

3 years later
#31 5 years ago

Hello, sorry to resurrect this old thread.

I’m a bit of a noob and I have the coil blow the flipper fuse instantly.

Can I replace my LOTR LE board with a rottendog board to solve the problem without having to solder on the board itself? I’m not able to find the bad transistor...

Thanks

#32 5 years ago

Would be cheaper and better to send this to an experienced board repair person.
And if the reason the fuse is blowing is not on the board but within cabinet, it may do the exact same thing with the replacement board.

#33 5 years ago
Quoted from PinPeet:

Hello, sorry to resurrect this okd thread.
I’m a bit of a noob and I have the the coil blow the flipper fuse instantly.
Can I replace my LOTR LE board with a rottendog board to solve the problem without having to solder on the board itself. I’m not able to find the bad transistor...
Thanks

The manual will tell you which transistor drives the flippers.

As per this thread, replace it with the upgraded transistor, with a heat sink if possible.

If you can’t do that work, there will be someone local to you who can. It’s not an expensive job, as GPE said above.

rd

#34 5 years ago
Quoted from flecom:

are you sure you are not thinking of inductors?
resistors do not do what you are describing

Adding to an old thread, but I will chime in anyways:

I deal with this somewhat often in my 'day job' designs...

Gate capacitance (inherent in ALL the MOSFET die, to different degrees), when combined with gate resistance, creates a time constant. FETs are resistive in between on and off states...that's when they dissipate the most power. Being completely 'off' or completely 'on' is NOT typically the issue (assuming they are rated correctly for the application)...it the time in between that can cause problems - if it violates what is called 'SOA', or Safe operating Area. Hergs comment about the different threshold voltages (Vth on the data sheet, is which is when the FET starts to conduct) does indeed also play a role. Increase the resistance and you increase the gate time constant, possibly violating the SOA limits since it's turning on slower. FET switch data sheets usually include SOA curves that you need to remain under.

I haven't looked up the data sheets for the FETs mentioned, I didn't want to derail the thread with a huge write up - I'm just referring to the standard guideline for using a FET in a switch topology. I can add more details if anyone is interested.

2 years later
#35 3 years ago

i have struck switch problems just now with some doofus using p20n10 mosfets
hit both flippers and a slingshot and the cpu boots with a verifying screen
on this 3 flipper game i used the tk42e12n1 mosfets , new 1n4007 and flicked off the associated smd cap (x3 sets of parts one per flipper circuit)
plus put a 100v mov across the cap on the 50v bridge
now seems good , testing will see its longterm.

#36 3 years ago
Quoted from Eddie:

[quoted image]
My final info on this issue.

stern saw the problem , but were silent?

1 month later
#37 3 years ago

New here.

After reading this thread last week, I decided to try and resolve my left flipper issue. I purchased some IRF540N Transistors and Replaced it today.
The original issue was it blowing a fuse at start up of a game. The flipper would go straight up and hold itself for 2 seconds then blow the fuse. After identifying the shorted transistor, I replaced it along with the fuse and All looked good until one push of the left flipper button and then, Stick, Blow fuse and a shorted transistor. What the heck?

Stern AC/DC Pro.

#38 3 years ago
Quoted from Rotellicaster:

New here.
After reading this thread last week, I decided to try and resolve my left flipper issue. I purchased some IRF540N Transistors and Replaced it today.
The original issue was it blowing a fuse at start up of a game. The flipper would go straight up and hold itself for 2 seconds then blow the fuse. After identifying the shorted transistor, I replaced it along with the fuse and All looked good until one push of the left flipper button and then, Stick, Blow fuse and a shorted transistor. What the heck?
Stern AC/DC Pro.

Test the diodes on the flipper coil.

#39 3 years ago
Quoted from Rotellicaster:

New here.
After reading this thread last week, I decided to try and resolve my left flipper issue. I purchased some IRF540N Transistors and Replaced it today.
The original issue was it blowing a fuse at start up of a game. The flipper would go straight up and hold itself for 2 seconds then blow the fuse. After identifying the shorted transistor, I replaced it along with the fuse and All looked good until one push of the left flipper button and then, Stick, Blow fuse and a shorted transistor. What the heck?
Stern AC/DC Pro.

Also check the coil resistance. See if the ohms are within specs for the coil.

#40 3 years ago
Quoted from Rotellicaster:

I purchased some IRF540N Transistors and Replaced it today.

You need logic level mosfets. STP22NE10L subs to a IRL540.

#41 3 years ago

I love this thread! It was the first thread I used to help me with my first pin in 2017. Got a TFLE and the second night we had it, my wife was holding a ball on the left flipper and it died. A total noob at the time, I freaked out about my new machine being broke and spent hours searching for a fix using the wrong words to explain but somehow found this thread.

Traced the issue to Q15 on the SAM board, watched a few YouTube videos to learn how to test a transistor with a DMM then I emailed Stern to verify removing the caps was ok and that was my first of many interactions with Chas.

Sad thing is I paid $40 for some local guy to replace it for me because at the time I didn’t know how to solder/desolder properly

#42 3 years ago
Quoted from CoreyStup:

You need logic level mosfets. STP22NE10L subs to a IRL540.

Will What I have not work or be any good?

#43 3 years ago

IRF540 will not work properly. They won't turn on fully when 5V is applied at the gate. You need logic level IRL540 or another comparable mosfet.

#44 3 years ago
Quoted from CoreyStup:

IRF540 will not work properly. They won't turn on fully when 5V is applied at the gate. You need logic level IRL540 or another comparable mosfet.

Thank you! I ordered the STP22NE10L and the Diodes.

#45 3 years ago
Quoted from CoreyStup:

IRF540 will not work properly. They won't turn on fully when 5V is applied at the gate. You need logic level IRL540 or another comparable mosfet.

Adding to Corey's comment, here's a data sheet SnipIt for the IRL540. Does look a little shy at Vgs = 5V (6V is listed, so interpolating).
pasted_image (resized).pngpasted_image (resized).png

For those not familiar with the FET's as a switch, you want them to be fully turned, meaning lowest possible resistance (Rds). The lower the resistance, the less heat dissipated. If it's somewhere in-between off and on - then it will dissipate power since it's essentially a higher value resistor and can be damaged.

A few more specs involved, but that's the basic idea (turn it fully 'on' or fully 'off').

#46 3 years ago

And while I'm at it, here's the STP22NE10L part.

pasted_image (resized).pngpasted_image (resized).png
#47 3 years ago

Thank you folks for your help! I'm back up and playing!!!

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