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 : )™

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

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 : )™

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.

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.

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

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.

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.

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

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.

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.

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).

My LOTR LE L flipper just blew its replacement IRL540N transistor.

Has anyone tried the heat sink route, and If so, what manufacturer and model # heat sink fit over both the flipper transistors in their space on the board?

By the way, thank you, all, for the explanation of the heat generation of the PWM design. That makes sense now.