Possible vibration of the pin causing the switch to close? If you widen the gap of the pop bumper switch under the playfield does it stop?

Check the diode on the coil as well. Does it also have a capacitor on the switch? shoot a pic and post.

Ghost.

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That coil looks shot, notice the burn on the label. I’d start there. Disconnect it and reevaluate

Those pop bumpers are all on the same column in the switch matrix and the upper right eject hole is on the same row as the bottom right pop bumper. Which pop bumper did you disconnect? Cannot tell from the picture.

One of the lugs on the coil had 2 red wires wires. That is the power side and they are wired from one coil to the next. If you just cut the 2 red wires off the coil, you broke the power supply chain to the downstream coils which will stop them from working.

Connect the wires back up to the coil.

Check the problem still exists.

Remove J13 from the driver board. This is the special switch input connector (fires the pops, slings, etc).

If the coil still locks on, you have a problem with the driver board.

If the coil does not lock on, the problem is in the trigger switch or wiring.

Following. I'm have the same issue with Top Right Jet bumper. I cut the blue/orange wire and I have now issues with game booting up. It plays fine. The board was just serviced too and never had that issue of locking up. I'm going to change the coil out and add some new parts to the jet bumper and see if that fixes the issue. Please share if you are able to fix this on your machine. Btw it's J12 that you need to unplug for those bumpers.

J13 is the switch input to the driver board for special solenoids.
J12 is the drive.

When trying to troubleshooting a locked coil, disconnecting the switch input connector, J13 can isolate the problem to the board or the switches. Disconnecting J12 only disconnects the drive transistor from the solenoids stopping the coil from locking on but really doesn't tell you anything.

Thank you for the clarification. Can you tell me the steps to check if it's the board or the switches? I appreciate the help in trying to locate the issue.

As Shwaggs stated in post 8....

Cool, so taking J13 off the driver board you eliminated the pop bumper switch from the list of suspects. That leaves us with J12, the ground path for the special solenoids (including the pop bumpers and probably the slingshots). The fact the coil is activating the moment you turn the game on with J12 plugged in tells us the pop bumper is getting a path to ground the instant the game is turned on. That usually indicates a bad/shorted driver transistor and/or pre-driver transistor on the driver board. You can test them both using the diode test on your meter. Looking at the schematic, the driver transistor is Q4, pre-driver is Q3. The lower left pop bumper is labeled solenoid 18, you can trace it on the schematic from the coil to 2J12 pin 4. There should be a blue wire with a red stripe at that connector--that's the ground wire coming from the pop bumper coil under the playfield. The transistors on the driver board provide the path to ground for the coil, and when they go bad, they will often cause a coil to lock on immediately upon turning on the game.

To summarize: the red wire at the pop bumper coil is the +28vdc supply. The blue/red wire on the other lug of the pop bumper is the ground wire, which runs up to the driver board at 2J12, pin 4. From pin 4, the ground circuit for the pop bumper continues to a TIP120 transistor (Q4).

When the mpu activates that transistor, it completes the path to ground for the coil and the coil fires (pop bumper pops). While I'm not necessarily recommending you do this, here's an easy way to demonstrate what's happening on a simpler level. If you remove the blue/red wire from 2J12 pin 4, the pop bumper should stop locking on. If you then stripped the end of that wire and *very briefly* touch the exposed end of the wire to the ground strap in the backbox, it will activate the coil. The transistor is acting like a switch in a way, when it gets activated it momentarily provides a path to ground. A bad or shorted transistor will often "stay on" causing the coil to lock on the moment you turn the game on. Note the TIP120 is the likely culprit but there are other components in that circuit that can go bad in addition to the TIP120 transistor... the pre-driver transistor, the chips before that, the diode on the coil, etc. Good luck!
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Excellent logic explanation Frunch.

You're welcome!

TIP120 or even better a TIP102 are both suitable replacements. I would recommend checking Q4 and Q3 with your meter on diode test. I'll admit, it definitely looks like Q4 fried. Are you familiar with the procedure for testing transistors?

Scratch that--you have a rottendog board. I am not sure if those transistors are suitable. Do you have the schematic for the driver board?

The factory Williams board uses TIP120 transistors. But these Rottendog boards use MOSFET transistors which are different, the part number is FQP13N10L (that's "one zero L" not "one oh L") that you need.

https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=FQP13N10L&_sacat=0&_dmd=1&rt=nc&LH_PrefLoc=1

Before replacing the transistor be sure to ohm check the coils that were locking on (pop bumper coils). They should all show a similar value. Anything that shows below 2 ohms or shows over limit or way out of whack from other similar coils is a bad coil and needs to be replaced. Even though the transistor at Q4 is likely to have caused the original problem, a shorted coil in that series may burn up your newly installed transistor and create more work!

You said you replaced mpu and power supply so I am assuming you still have original driver board in the game?

Be sure your coils are ok then replace transistor. If anything still locks on after you check that coils are ok and replace Q4, turn game off, check resistance at the coil and then look for another bad transistor (hopefully that doesnt happen!).

Good luck. Firepower is a cool game!

I would replace it with another 13N10L MOSFET.

Before you do, check the resistance of that coil. It should be around 5.3 ohms. If you get zero or close to it, reverse the polarity of the meter leads and measure again.

If the coil resistance is good, make sure to replace the diode on that coil and make sure it is installed in the correct orientation. I suspect the diode is bad and what killed the MOSFET.

Buy some extras so you will have some on hand the next time you need them.

Thanks guys for helping creativenuts. The info you all are providing is helping me as well. Frunch - Appreciate the explanation for this newbie. Schwaggs - Thanks as well for the steps as well.

I hope you guys don't mind if I chime in with questions or should I start my own thread?

Might be better to start a new thread just to keep things orderly for OP.

I'd be happy to try to help you further, as I'm sure many others will be as well.

Nice, glad you managed to remove the old one ok. Any update?

Take your time! Just anxious to see if that's the solution.

Next transistor you need to remove, try cutting the body of the transistor off the legs first. Then you can desolder and remove one leg at at time.

Remove the 3 nuts that hold the coil bracket to the bottom of the playfield. be careful to catch the spring on the plunger as you remove the bracket.

Once that is removed, you remove screws "A" and you can remove the old coil and mount the new coil and sleeve in place.

Reverse above (remember the spring) to reassemble.

Lot's of great infomation on this thread.

I wonder sometimes if pinsiders have way more knowledge just from working on their machines... figuring things out.. getting tips/info from other pinsiders than the guys that had routes & worked on machines on a daily basis?

Oh, one other thing:

Make sure your new coil has a diode installed. Pay careful attention to the lugs you solder the wires - Double red wire (power supply) goes to the lug with the banded side of the diode.

All that matters is that the wires go to the correct sides of the diode. The diode can point either way, but again it's very important you put the wires on the correct sides of the diode (the banded side vs non-banded side).

Awesome! Congratulations on the fix!

Great stuff!! Enjoy!

That's awesome!! Great work.

Great work!

Love it when a pin is back up and working. Congrats