Dead Stern Flipper

So watching Elwin’s flipper die on his ST during this video: Video: Elwin + Star Trek 1.61 = set aside 32 minutes reminded me I ran into the exact same problem on my Metallica, exact same flipper as well.

Is there a better transistor I should be replacing that with so I don’t run into the issue again?

Get someone to confirm, but I think this is what you’re looking for:

I used these: which appear to be the same. Can’t speak to longevity, they’ve only been in for a few months, but working great.

You know you need a new transistor if: you’ve replaced the flipper fuse under the playfield, and when you turn the machine on, the flipper activates immediately. (Turn the machine off quickly, and you’ll save the fuse from blowing). Then replace the transistor on the board (Q15 or Q16, depending on which flipper - which you could double check with a multimeter to ensure it’s dead before actually replacing it).

A lot of people will suggest that you might as well replace both transistors while you’re in there, because the stock ones will go out eventually anyway.

GPE has the IRL540 at $1.40 not including bulk discounts.

Ok so the IRL540 is what I need, one of my local suppliers will have it im sure. Thx

That’s what was in there lol. Sadly there is no fix for bad design other than buy a WMS or new Spike system game. The irony is the right flipper was really crappy so I put a LOTR coil (3.4 ohms!) in there and that transistor is holding up while the factory one on the left has blown 2 now.

So this is a problem that could potentially happen with all Sterns from the first Whitestars right up until Spike? Damn. Best grab a couple of spares for my RBION then. Even though it’s HUO and likely has a lot of life left, can’t be too safe.

For reasons unknown to me, I think the SAM games are more prone to blowing out flipper transistors. I’ve had the LOTR special coils in my location Ripleys for years and never had a problem. The coil wrappers have numerous burn marks too. My (SAM) AC/DC pro has already blown one flipper transistor.

This problem only really started happening with 24 and games after it. It should not happen any more after Mustang.

If you remove the caps associated with the flipper transistors (Q15 and Q16) the problem should go away.


When doing a Q15 or Q16 Stern repair do you always remove the caps and use the IRL540?

Caps for sure. I haven’t noticed any difference between the 20N or IRL540 once the caps are removed

Good to know about the caps. For some reason the irl540 seems to be easier to find online.

I op a LOTR that has blown through at least 3 transistors in the last year. I think two of those times found a broken diode on the flipper coil, the 3rd time I replaced the diode even though it wasn’t obviously broken.

Ha, I just picked up a LOTR where someone installed transistor sockets on the driver board!


Huh I wonder how that would hold up. Guess as long as it is a good quality socket it would be ok. I’m not sure how many more transistor replacements the solder pads will survive on this particular LOTR driver board.

Oh I have a funny story about this.

So during development, we were constantly blowing the ring tranny for one reason or another. After about the 5th time, Chas finally socketed that spot, and then it never blew again.

Moral: Sockets are MAGIC!


I help a guy with a LOTR that looks like it was in a meth lab for 10 years. Any part with any metal on it is corroded, including the transistors. I replaced one of the flipper transistors with an IRL540 a while ago and he called me back a few months later and said the right flipper was bad again. Turned out the right flipper button contacts had corroded over. Cleaned them up and it worked fine. No sockets for this LOTR. (yet)

can you show a pic of the caps?

We had a technical discussion about Stern MOSFETs a while back on the UK forum. Seems pertinent to the discussion here:

C52 and 53 surface mount caps by Q15 & 16