Very common problem on sterns. I believe it's q15 and q16 that are the lower flippers. Replace with the better IRL540s, when one goes, and when I have the board out I do them both.

As for checking, use a DMM, and compare the results with the other flipper transistor.

+1

The same thing happened to me too, replaced Q15 and Q16 with IRL540N and have not had issues since

Check the transistor first though and confirm it is in fact that. Last thing you want to do is all that work and find out it was something like an internal winding wire of the coil that broke off that wasn't visible.

Confirm the transistor is not reading the same as the other, and then replace.

should be able to test on the board. Set to diode. one lead on the center and check both outsides. Should be .4 to .6.

I am pretty sure this confirms it is the transistor.

With a new fuse in place, does the flipper energize as soon as you power on the game? Also, if it does, you can usually save the fuse by powering off immediately.

Do NOT turn on anymore testing fuses. The q16, has shorted - that reading indicates a dead short. Replace both with IRL540s, as the other side will likely go on you at some point as welll. They are stronger than what is used, and recommended by stern techs (despite stern STILL not upping them in production).

Now you know how to check bad power transistors!

I had this same problem but also check the diode on the coil which could have caused the transistor to short. Just replacing the q16 transistor may not fix it so check the diode replace it if bad, replace the transistor then the fuse and try it again.

The readings do indicate a shorted transistor, but I would also ck the resistance of the coil. Every time I've seen a shorted flipper transistor on a Stern, the flipper pops up on power on. I have not personally dealt with this on LOTR, but I've seen it on Monopoly, IM, and S-M. In the case of Monopoly, it also took out a Uxx chip.

LOTR or LOTR LE?

Diodes on the coils then I assume. LOTR LE flipper coils use no diodes on the coils and will blow a fuse if you put coils with diodes on them in the game. Seems like this is not your issue though.

Could be the pre driver transistor. I am no expert, but there are these smaller transistors that are on some boards that can go bad as well.

a) have you checked to see if the diode across the coil is shorted?
b) if you disconnect one (or both) lead(s) to the coil, does it still blow the right flipper fuse?
c) your resistance across the coil seems off. reverse the leads and try the readings and see if they are the same across the coils

If that fuse blows on power up, that indicates a short somewhere on the flipper circuit. I would suspect that your coil is shorted out. Usually the way this works is that the transistor locks on, burns the coil and shorts the coil. If you only replace the transistor, you'll still have an issue as the coil is shorted. I would remove the coil from the circuit (unsolder it) and see if the fuse blows. If it doesn't, properly test the coil resistance. If it's a dead short, or anything near it, repave it. You can compare the reading to the other working flipper coil. FET transistors are a little tricky to test in circuit, so start simple before doing any more board work.

I do not believe that a locked on driver transistor would blow a fuse on power up, but I have been wrong lots of times before. I would focus on the coil first.

Marc

You could just check the coils on it with the power off. If they are different readings, then you know you have a problem.

There is no predriver for these systems as there is for Williams systems. Sounds like the coil has shorted. Desolder one of the power lugs and measure the resistance for the coil.

The transistor may still be ok, you are not getting a dead short or open, the reading could be indicative of another issue and the fuse kicked it out before doing damage on the board.

Just do them both. You want it out of the circuit.

Just one is fine, there is no complete circuit with at least one out of the loop.

Also your flipper coil test readings were wrong. You didn't have your meter set to ohms or the meter just plain sucks. You'll get around 4 ohms testing a working flipper coil. This means you did not eliminate the coil by testing it previously.

At the time I think he was checking them with a shorted transistor.

Now that your right flipper is unsoldered, replace the fuse and boot the game. If the fuse does not blow, replace the coil. The readings on the coil resistance should be the same (or roughly the same). The fact that your readings are that off leads me to believe your right flipper coil is in fact, shorted.

Marc

You can test the transistor! Before putting the new coil in, test and make sure it's not open/shorted.

You are close to having the game back.

Marc

I don't think you need to pull the board to check the transistor.

Check the transistor on the board, as you did before, if it measures good (in the range of the other one), it has not been taken out again. Your flipper coil readings for the suspect one are too low, it has started to short somewhere, and needs to be replaced.

Once you do that, and the transistor is confirmed still good, you should be good to go. Make sure you check the transistor again though BEFORE installing the coil and powering up. The coil and transistor can short each other out - the fuse just doesn't seem to kick out in time with these systems.

As well, take photos of the wires to the lugs before completely desoldering if the coil. Sounds easy, but you would be surprised how many times people hook them up backwards, and then are in for more issues.

Also, always check the diode on the coils. I have seen where they have been installed factor backwards.

I think that is fine, it would be closer to 0 if there was a short, and with the coil in circuit the resistance would be different.

hmm, maybe something has gone wrong then. Usually they are good or shorted/open, but that is odd... Might be safer to swap just in case, since they are cheap.