I would try a new transistor. When it's on the board. Grab a meter and check continuity of each leg of the transistor ( not it's solder joint on the board ) to a solder joint along the same trace away from the repair area.

This is to check through board and across board continuity. A crack in a trace or something you can't see can drive you nuts.

LTG : )

Not familiar with whitestar boards, but aren't there pre driver transistors that could be failed in the closed position?

When I fixed a Data East boardset for a similar issue, there where three transistors in series which could've been the culprit. I would go "upstream" of your failing transistor and test the next one with a DMM.

Could bee that small ribbon cable between the CPU board and Driver board... it's not keyed, so you can try flipping it over ( on both ends ) to see if the problem changes.

Would replace diode on coil as well. Possibly open?

This....a bad coil diode will do this all day every day!

Another thing to check: Since it's not following the board it's definitely on the playfield or the wiring. On my LOTR the main under playfield harness runs REAL close to the left of the metal cabinet playfield rails. Ive had that under playfield harness snag on that left metal rail and short out a couple of wires.

Its a quick easy check to check the diode; however, an open diode will not do this:

In order for the flipper to do this with no interaction you have to have a path through the flipper coil to ground, AND for it to blow the transistor, this path has to be through the transistor.

In order to stop blowing fuses while troubleshooting this issue, stop replacing your blown fuse and start doing ground checks with your multi-meter connected
between ground and the flipper coil (it doesn't matter which side). Only replace the fuse once you have a condition where a ground to the flipper coil only exists when you are pressing the flipper button.

There are not, these are driven directly from U2 on the I/O Power Driver Board.

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Could a failed C256 .01uF capacitor at the top of that diagram cause the repeated blowing transistor issue?

Have you tried replacing the coil? That’s what the issue sounds like to be. A bad coil will blow your transistor if it draw too much current. Also a bad diode could do it, new coil = new diodes also.

Did you ever find the solution?

My LOTR is doing this too. But on the right flipper. The flipper Initially started dropping during gameplay then stoped working completely. I lifted the playfield to find the plastic plate on the coil had snapped and the diode had lifted off on one leg.

I replaced the diode, but when I turned it on the flipper didn’t work. The original issue
Blew the fuse.

when fuse was replaced I turned the machine on and the flipper locked on.

Transistor was fried. So changed the transistor. Turned it back on. Flipper didn’t jump up (Yay!). Started a game flipper worked and the second time I hit the flipper button the fuse blew.

Replaced the fuse and the flipper jumped up again! Board out, replaced the transistor again.

So I have been through several fuses, transistors and diodes.

I’m waiting for a new coil to arrive in the post so I can put that in and eliminate the coil as a cause. I note in your post that you tried a new coil and that didn’t fix it for you. I hope you found the problem,

I've just put in a new coil - same issue.

Game starts up but as soon as I press the right flipper button the right flipper locks on - blows the transistor, then the fuse goes.

I've changed the flipper button switch - same issue

I have not changed the end of stroke switch yet

I've followed @Pin_Guy's advice about checking grounds between the flipper coil and ground - There is continuity between the coil and ground, however when I unplug from the board and test it there is not. Testing the pin it connects to = ground.

So new transistor in again - this is the 5th time I have changed it now.

rechecked the coil - no longer grounded.

interestingly neither of the flipper coils show continuity with ground when I close the switch at the flipper buttons. Are they supposed to?

Anyone have any other suggestions what to look for next? running out of Ideas and assuming now it is most likely a board issue.

Good morning,

Did you resolve your issue ?
My left flipper died recently, so I need to start debugging it. Reading through all material on pinside, it appears this can be rather complicated if I'm unlucky

No, the only continuity they should have to ground is through the drive transistor, this has no direct ties to the flipper button.

Blown drive transistors are normally caused by either an incorrect replacement part, or a failure of the flyback diode to eliminate the huge voltage spike created when the magnetic field around the coil collapses.

What are the specs of this flyback diode ? Need to check whether it's working, I had two blown fuses in less than a week (but no blown transistors)

These are typically 1N4004 diodes. It would be very unusual for a bad or missing flyback diode to result in a blown fuse without first taking out the drive transistor.

I checked the diode, it was OK

I used my current probe to check on amp during test, as it turns out:
- I have a current peak slightly above 4A on the left flipper
- I do not have this current peak on the right flipper

Kind of explain why my fuse kept blowing.

Now that does not explain why I have a higher current peak, is this typical of a transistor starting to go bad ?
Sidenote: I have the high power coils, would that explain the behaviour ?

On the questions now:
- I looked at the schematics, could not find the reference to the flipper transistors, could someone give me a pointer ?
- Should I simply replace my 3A fuse with a 4A ?

Thanks

Assuming that the same drive transistors, and coil are in operation for both flippers the peak current measurement should be about the same for both. The mathematical equation is [ I = V ÷ R ] where I = current, V equals source voltage (50V) and R equals the resistance of the coil (3.4 ohms) this comes out to 14.7A when energized. A "high power" coil will have less resistance and therefore pull more current that the stock coil, this is also offset slightly as the resistance of a coil will increase with heat and result in a lower current draw which reduces power and is the cause of flipper fade.

The stock coil spec is 735W of power; the formula for Power (P) in watts is current (I) multiplied by voltage (V), therefore the stock coil rated at 735W with a 50V source should pull 14.7 Amps of current against the 3 Amp fuse... math is fun when all the numbers add up properly.

A slow blow fuse is designed to not blow with these short duration current spikes, that being said they WILL experience fuse fatigue from the repetitive heating and cooling of the fuse and they will eventually blow.

I'm curious as to why you didn't list a peak current value for the coil that isn't blowing a fuse, this would be great information to have especially if you have the same coil in both flippers; your 4A measurement actually seems excessively low for a flipper coil, grated the short duration of the full drive would be difficult for all but the highest end meters to capture. It may be possible that this drastically different measurement between coils could be an indication that full power is being applied to the coil for a longer period of time on one coil allowing you to make this measurement which could be the result of a non functioning EOS switch causing the game to apply for power to the coil for the maximum allowable time set in software. This software setting would be based on how long a stock coil could be powered on for without blowing the fuse or causing excessive fuse fatigue; these max duration flipper coil settings are also adjustable in game settings to make them shorter in order to reduce coil heating and retain coil power.

I realize indeed I did not provide the value for the right flipper. From what I could see it's less than 3A, about 2.4A.

The coils were acquired simultaneously a few months ago, same part number. I would certainly hope they have the same characteristics

Indeed my current prove has a slow response time so it's hard to see what is the real peak current. I was thinking of setting up my Pico scope, provided it can sustain the Amp level (I don't think I have an Amp probe for the scope, so will have to put it in circuit)

With regards to the maximum 'on' time, wouldn't that be in seconds?

Also I did actually measure the Amp level when maintaining the coil on, in both cases (left and right) they are far below the 1A level

I'm calling on memory here, but I believe its 80ms, or 0.08 seconds.

Power off, measure the resistance across each coil. If you're using the Pinball Life LOTR special coils, that makes a big difference. They draw significantly more current than the factory coils. Measuring the resistance across the lugs of each will show you why. Much lower resistance on the PL cols. You should be okay going up to 4 amp slow blow, but don't go any higher. Game is rated at 8 amps.

If you do have a transistor short, make sure to use a new transistor that's rated higher. IRL540N or better. Also, something that wasn't mentioned earlier in the thread is that when a transistor goes bad, you need to check the other components that circuit. Pic above shows that each transistor has a resistor and a capacitor in it's circuit. Even when you have the right size fuse, shorted transistors can take out other components. The flipper coils are the strongest coils in the game and yours have been upgraded to ridiculous strength.

FYI...I rewrote a vast portion if post #21 trying to get it to make more sense.

Your explanations are pretty clear, one learn everyday, I never had the opportunity to figure ot what these EOS switches are, now I know...

I'll check it

Two questions though:
- I assume that to measure coil resistance it's best to remove the fuse, so that one end is floating, the other should already be floating if the pinball is off, right?
- I seem to recall there is a coil strength setting in the game, how does this operate technically, since there's only one command transistor?

Regards

You can just measure across them in circuit, you can remove the fuse if you want but its likely unnecessary.

So measurement show 3.7 ohms on both coils, it seems they are identical.

The EOS switches seems fine mechanically, but how can I test if it triggers soon enough?

Regards

It should close right at the end of the flipper stroke. You will need to make sure it actually reads closed in your switch test to ensure it works. The resistance measurement you provided is higher than the stock coil, which is odd.

I happen to have a NOS LOTR flipper coil lying around and I just measured it at 3.2 ohms, this was a relative measurement made by zeroing my meter leads to remove their own resistance from the measurement.

Many thanks for your help, I'll investigate the EOS switch behavior. I'll also check the coils resistance again, I had not zeroed my test leads (although to be fair I'm not even sure my multimeter has that capability). But the fact they are identical is at least a good sign.

My solder points on the left coil seem weak though, I'll reflow them.

Regards

Just measured the coil resistance after zeroing the test leads and using a better multimeter, it's at 3.2 ohm.

EOS switch seems fine

I've resoldered, and put a 4A fuse, if the transistor blows I'll replace it with the recommended reference

Regards

I solved my problem.

In trouble shooting, I replaced the coil, diode, EOS, cabinet switch. But no change. And in doing this worked my way through 5 transistors and fuses.

That was enough for me, I I took it to a tech, who replaced the IO chip, and it’s working now.

So the initial problem was the diode breaking at the coil, but this obviously damaged the io chip.