Fuses dont usually blow for no reason. You probably have something shorted. Start by disconnecting the playfield wiring to the high powered coils and see if the fuse still blows. If so its in the board itself. If it it's in the playfield. In either case, an ohm meter will help you track it down further.

I don't have extensive electrical experience/knowledge in pinball.

But with a fuse blowing due to a shorted to ground circuit somewhere. Will the "headlight in fuse" method work to help find the short vs unplugging stuff and then inserting a fuse to see if blows

I was an auto tech 20 years ago and I used the headlight method often in troubleshooting electrical shorts to ground

The "headlight in fuse" method

I would attach jumper wires to the connectors of a seal beam car headlight. And then attached the other end of the jumper clips to the fuse holder.

The fuse blowing is because there is no load between the power and power. The headlight in fuse handles the load. When the short to ground condition is present. The headlight will light up. The intensity will depend if there are other load devices on that circuit and if they are in the on position

Imagine connecting a wire between your car battery terminals. It will heat up instant. That's a short to ground condition.

But when u attach a test light to the car battery terminals. All is fine The bulb takes up the load.

But with automotives. I'm working with 12volt DC current with a 12v DC sealed beam headlight.

I don't know the voltage or current of a pinball machine

A pinball machine is a giant vibrating box. So much can come loose. On my Star Trek. My left sling would go ball on ball to shooter lane. I didn't understand why. Until after my left sling stopped working. I looked at it closes and noticed the upper left sling switch was closed. Over usages. The switch contacts got closer and closer together til it was always closed. I think if left the way. Something bad would have happened. But who knows

No worries. I was inquirimg if there was another method of finding shorts without blowing fuses.

Yup, start testing the coils with game off, meter set to resistance/ohms and find the one that is shorted and reading open (or nearly open). It will read way different than the others.

Good luck.

Marc

I would start by taking a close look at the ball trough coil that kicks the ball into the launcher, I'm assuming this is the only coil that would fire just by pressing the start button. If this coil is shorted or the wire is broken off and grounded you will see this fuse blow in the manner you described.

I'm following your thread to learn more about pinball troubleshooting and repair

I dont think u can get an accurate reading on diodes that are connected to a circuit. So isolating them is the needed to measure accurate results

Question. How would hooking up the new diode in parellel with the suspected bad diode change the results. Wouldnt the flow of power take the path of least resistance and flow thru the suspected bad diode?

It's possible that you have a bad diode, typically they will short when they fail and read 0 ohms across them, you can remove J8 and J9 to kind of isolate them from the circuit but they are still in parallel with the coil so you will need a good meter to make these small resistance checks. With those two cables removed and power off of course, you can check all the coils in the game without unsoldering anything. Write down all the resistance measurements and compare like coils ... for example the 3 pop bumpers should all be very close to the same resistance since they are all the same type coil.

Lets assume that you have a shorted diode, in order for the fuse to blow you still have to close the circuit to the coil. So the question still remains, what coils are energized by the start button? I'm asking that because those are the only ones that really need to be checked. I would say that it's possible for a failed coil diode to in turn take out the same driver transistor that its there to protect, but if that was the case, you would blow the fuse as soon as the game was powered on since the coil circuit would be completed all the time.

A second question, which relates to the first; in the switch test menu, are there any switches that read closed when they shouldn't? Where I'm going with this is something like the switch that energizes the magnet being stuck on so that the magnet fires as soon as a game starts when it really shouldn't be on.

Well that doesn't make any sense; can you confirm the fuse your are blowing is the 50V fuse on the I/O Power driver board? Also, what is the part number of your board? I went with the assumption that you are blowing the 50V fuse, but the manual shows F10 as the +20V circuit fuse.

When you speak with Stern, they are going to ask you to perform some tests in order to isolate the problem to the playfield component or circuit board causing the problem, pretty similar to what you are already doing. If they determine that its a board issue, they will want you to go through your distributer to have the part shipped to you and its up to the distributer on how they handle this. Now for the guy out there that doesn't have any skills working on a machine they are going to ask if you know someone that can come over and have a look at the problem; the Stern tech really cant help someone that cant make the checks.

IMG_1428a_(resized).jpg

IMG_1429_(resized).JPG

They swap boards out.

I'm have mixed feelings about it stopping blowing fuses immediately since that would be way easier to isolate than an intermittent problem but I'm glad we are on the same page on which fuse is blowing. This F10 fuse has nothing to do with your high current solenoids at J-9 and J-10, it powers the low current solenoids and flash lamps connected to J6 and J7 of the power driver. I did look at the diagram from post #3 but I just don't see any connection to F10. Earlier when you mentioned that it was immediately blowing the fuse on power on I was starting to suspect BR2 as the cause and its likely Stern is going to recommend replacing the I/O Power Driver which may fix everything. If you have time, play a game with no flashers by removing the connector from J6 and see how it goes, I would prepare for the new I/O board not fixing the problem ... but that's me. Try not to get down or frustrated, pinball machines do break from time to time, but they are always repairable

I was looking at the schematics to determine why you lost flipper power and all I can come up with is that there is a Interlock20 status output coming off the 18V AC line after the F10 fuse, this status along with the 50v status and a couple others become an 8bit data word that is monitored by the onboard processor. I would have to guess that a failure of any of these critical voltages tells the computer to immediately halt game play, which is why you would see the flippers stop responding. I could be wrong but would love to hear what the guy from Stern says.

So much happened since I was here. So the way I go about it is this. Once I have eliminated the board as the issue, I get my ohm meter and put it on continuity mode where it beeps when the ends touch. Then I put the black lead into the ground braid and using the red lead I touch each pin of the connector I removed until I find the shorted one. Then I know which wire has the short. Trace that back to the coil etc

Did you find the solution?

Same problem happening to my Star Trek LE model. Fuse F10 is blowing. On mine, it's happening when you start a game, right after it kicks out the first pinball to the shooting area.

Did either of you figure out the cause?

I ended up solving the problem.

Short story: Transistor Q29 was bad

Long story, being my first pinball problem, I troubleshot the problem as follows:

1. First I got some replacement 5AMP slow blow fuses. Ordered Cooper Bussmann fuses from Amazon seller "Game Room Guys"
2. Turned off machine, unplugged it, replaced with new fuse.
3. Opened up coin door which disables the 20VDC rails which prevents the fuse from blowing.
4. Turned on the machine and went directly into the service menu.
5. Enabled the 20VDC rails by pulling the little knob behind the coin door
6. Proceeded to test individually each and every lamp/flasher/coil with the service menu.
7. Determined that the Flasher for the Left Loop didn't work right, it was stuck on (if I recall) and remained on for a second or two even after turning the power off (spooky!)
8. Thinking maybe the flasher was broken, ordered a replacement from Pinball Life: https://www.pinballlife.com/ablaze-8-smd-led-12-volt-89-bayonet-base-flasher-lamp.html
9. Replaced flasher with new one, it did the same thing, remained on
10. Looked in Star Trek Manual and saw that Left Loop Flash was running from drive transistor Q29
11. Located transistor Q29 on the circuit board in the back cabinet box and tested it with my multimeter. Learned how from here: https://pinside.com/pinball/forum/topic/how-to-test-a-transistor#post-199399
12. Sure enough, Q29 tested bad
13. Ordered a replacement transistor from DigiKey, went with a better more robust version the TIP102G: https://www.digikey.com/product-detail/en/on-semiconductor/TIP102G/TIP102GOS-ND/920319
14. Took a ton of pictures of all the cables and connections to the PCB then I removed the PCB from the back of the box
15. Desoldered the transistor and removed it. Then soldered on the TIP102G replacement
16. Hooked up the PCB back in the box just like it was connected before
17. Re-tested each lamp individually again and BINGO the flasher for the left loop was now working perfectly
18. Played a test game, worked great

I've since played multiple games and have had no troubles at all.

Hopefully this list of troubleshooting steps I performed might help someone else out there