(Topic ID: 129955)

Stern Transistor question


By CookyJar

4 years ago



Topic Stats

  • 19 posts
  • 11 Pinsiders participating
  • Latest reply 4 years ago by CookyJar
  • Topic is favorited by 3 Pinsiders

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#1 4 years ago

Last year the right flipper on my LOTR went dead, on the recommendation of fellow pinsiders I replaced the original Stern transistor with a stronger IRL540N.

Last week the flipper went dead again. I called up Clive at Coin Op Cauldron and he reccommended replacing with a P24NF10L transistor. I have been unable to find this specific transistor, the closest that I have found is the type from Mouser.com: http://www.mouser.com/ProductDetail/STMicroelectronics/STP24NF10/?qs=sGAEpiMZZMsX0CFs5rpLHo2XEMS0C9r8

Is this the correct transistor and if not can someone point me in the right direction for the correct transistor?

#2 4 years ago

https://www.greatplainselectronics.com/products.asp?cat=106

Ed has a STP2nf10 , don't know if it's the same thing.

I'd stick another IRL540 in. Be sure you have through and across board continuity around the transistor legs.

LTG : )™

#3 4 years ago

Yeah, that transistor you linked should work fine, but it does have a max amp rating of 24A, whereas the IRL540 has a max rating 26A so a little beefier (both are overkill anyway).

I would just go with irl540
https://www.greatplainselectronics.com/search.asp

#4 4 years ago

If the transistors are overkill, why do they fail so often?

#5 4 years ago

I've been told this is a common occurrence with LOTR. But it seems to be something in the cabinet not the board, maybe a design flaw of some sort since it's so prolific. I still have a few more IRL540's from last year that I can try again, Clive just seemed to think his recommendation would work better.

If anyone has any ideas as to what may be causing this problem, I'm all ears.

#6 4 years ago
Quoted from RacerRik:

If the transistors are overkill, why do they fail so often?

There are some crappy components out there.

And when you put in a new transistor, grab a meter and spend a couple minutes checking the transistor legs for continuity to a spot a little farther away. To be sure you didn't lose through or across board continuity. I had that happen on a pin, cracked trace by the leg. And as soon as it opened up it takes out the transistor.

LTG : )™

#7 4 years ago

Thanks Lloyd will pull the board tomorrow and test out for any cracks then replace and test again.

#8 4 years ago

From what I have read, this commonly happens if you hold the flipper up for too long. Since the flippers use PWM for hold power, and this a FET type transistor, I suspect that the transistor is dissipating a lot of heat from operating too much in the switching state versus full on or full off. The current rating only applies for transistors operating in the fully on state.

One way to test this I guess would be to hold the flipper up and put your finger on the transistor. If it is getting hot, that would be an indicator that these are failing not from too much current but rather from exceeding the junction temperature capability of the transistor. And if that is the case, a small heat sink would probably solve the problem.

#9 4 years ago

Isn't LOTR also a game that many people have installed a stronger-than-factory flipper coil? That too may be adding to the driver's demise.

#10 4 years ago
Quoted from RacerRik:

From what I have read, this commonly happens if you hold the flipper up for too long. Since the flippers use PWM for hold power, and this a FET type transistor, I suspect that the transistor is dissipating a lot of heat from operating too much in the switching state versus full on or full off. The current rating only applies for transistors operating in the fully on state.

Oddly, I haven't had any problem with the left flipper transistor. Only the right which has blown the stronger transistor.

Quoted from CactusJack:

Isn't LOTR also a game that many people have installed a stronger-than-factory flipper coil? That too may be adding to the driver's demise.

I've read about people installing stronger than factory flipper coils, but I've kept mine to the original.

#11 4 years ago

My flipper got locked on my Ripley's, had to replace the transistor. Seems to be a Stern issue from that era of games.

#12 4 years ago
Quoted from mikedetroit:

My flipper got locked on my Ripley's, had to replace the transistor. Seems to be a Stern issue from that era of games.

The flipper on my LOTR won't lock, it just dies. Though I did have the lock on problem with my Monopoly.

#13 4 years ago

If it dies because the fuse blows, it's likely the transistor failing short (locking), then causing the fuse to blow. If your problem is that the flipper doesn't work, but the fuse is still good, you are seeing different symptoms than the usual problem.

Quoted from RacerRik:

Since the flippers use PWM for hold power, and this a FET type transistor, I suspect that the transistor is dissipating a lot of heat from operating too much in the switching state versus full on or full off.

Eddie from Modern Pinball NYC has said a couple of times that he removes a capacitor that is on the signal that control the base of the FET. He has not, from what I've seen, explained why, but I can only guess that he's trying to change way the FET is controlled to avoid it from overheating. I'd love to know the full story on this.

#14 4 years ago

Are your end of stoke switches operating properly? Many times the actuator arms break off so when you hold a flipper on, it's operating at full pulse all of the time. Kevin

#15 4 years ago

Be sure your software on Lord Of The Rings is the latest version on the CPU board AND the Display.
There was a service bulletin where the Ring Magnet was blowing the fuse due to constant use and a software tweak toned down the useage to keep the fuse from blowing needlessly.
Service Bulletin:
http://www.sternpinball.com/upload/downloads/sb151.pdf

Not saying this is the flipper problem,but the service bulletin mentions the flipper coils heating up and getting weaker during play. This could cause transistors to blow over a long period of play.

I had a Lord Of The Rings on route that blew the magnet fuse 2 times and caused service calls. Upgrading the Eproms fixed this and I applied this fix to the other Lord Of The Rings we had on route.

Never saw this problem again. That was probably 3 years ago.

FYI the current version EPROM is now at Rev 10, further than Rev 8 mentioned in the service bulletin.
Go with the latest and greatest.
Hope this solves your problem.

#16 4 years ago
Quoted from herg:

If it dies because the fuse blows, it's likely the transistor failing short (locking), then causing the fuse to blow. If your problem is that the flipper doesn't work, but the fuse is still good, you are seeing different symptoms than the usual problem.

Last time the fuse was blowing. This time the fuse isn't blowing.

Quoted from kms_pinball:

Are your end of stoke switches operating properly? Many times the actuator arms break off so when you hold a flipper on, it's operating at full pulse all of the time.

Checked EOS and they're positioned fine.

Quoted from Mrjamma:

Be sure your software on Lord of the Rings is the latest version on the CPU board AND the Display.
There was a service bulletin where the Ring Magnet was blowing the fuse due to constant use and a software tweak toned down the useage to keep the fuse from blowing needlessly.

Yep, just double checked and I have V.10 ROM and I have to check again for the Display. Haven't had a problem with the Ring blowing a fuse yet.

Going to tool around in it tonight if I get the chance and see if I can figure anything out. If not, I'll pull the board over the weekend and try a new transistor and see how that goes.

#17 4 years ago
Quoted from herg:

Eddie from Modern Pinball NYC has said a couple of times that he removes a capacitor that is on the signal that control the base of the FET. He has not, from what I've seen, explained why, but I can only guess that he's trying to change way the FET is controlled to avoid it from overheating. I'd love to know the full story on this.

If the cap on the gate of the FET is to limit the dI/dt value then I doubt this is extending the life of the cap but is actually making it more susceptible to failure.

#18 4 years ago

The Stern circuit will pulse the coil even if the EOS switch is not working. It assumes the flipper is fully engaged soon after the button is pressed and starts pulsing to prevent the coil from burning in a holding situation. The purpose of the EOS in modern machines is to know when (if) the flipper bat is pushed back so it can apply full power to bring it back up.

MOSFETs do not generate meaningful heat when "off" and very minimal heat when "on" due to their low "on" resistance. When operated between on and off, significant heat can be generated. MOSFETs are best used as switches, either on or off. It is during the transition from "on to off" or "off to on" when some heat can be generated. The slower this transition is made, the more potential there is for heat to be generated. While the flipper is in hold state, the Pulse Width Modulation (PWM) function rapidly turns the MOSFET on and off many times per second to prevent the flipper coil from overheating. If the transition occurs "slowly", significant heat could be generated during an extended flipper hold. This is also why someone suggested removing the .01 capacitor that is on the MOSFET gate lead. Capacitors slow the change of voltage both on and off and could cause the MOSFET to be in the on-off or off-on transition slightly longer than without the cap. However, the cap is most likely there to reduce noise in the circuit or for the purpose Ed mentioned above.

I doubt the capacitor is the cause of the problem. If it was, they would have removed it from the design on future machines, which they have not.

I suspect the clamping diode associated with that MOSFET has gone bad or is weak. When you replace the MOSFET, put a new 1N4004 or better yet, a 1N4007 diode in the circuit. The diode numbers match the MOSFET numbers (i.e. Q14's diode is D14, etc).

#19 4 years ago

Finally got to going around through the machine. Went to touch the flipper transistors to see how much if any heat was coming off them and the right flipper transistor feels loose. After wiggling it around the flipper comes alive, so I pull the board and the solder that I put on last year has loosened off the board! So now it's just a simple case of re flowing the solder, Lloyd was right about the through board continuity.

Thanks to everyone for all the tips and help!

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