Problem: Fathom blows the 1 amp slow blow beneath the playfield as soon as the game is powered on. Flippers work, no other coils work.

I checked the ohm level of each non-flipper coil. Each visually looks good and reads around 11 ohms. The larger drop target coils read around 25.

I have an Alltek solenoid driver board. Visually looks good, LEDs cycle normally. All transistors checked good.

I have not pulled and traced the wires from the fuse holder, and that would be pretty invasive and a last resort.

Anything I missed? Each coil has a molex, so I was thinking to disconnect all the coils, power the game and connect each coil individually to pinpoint the problem child.

image (resized).jpg

Would a bad diode still register 11 ohms during a test? I touched each lead of the DMM to the lugs with normal readings.

Thanks. Yeah, each transistor on the Alltek board checks good.

So I reinstalled the fuse and made sure each coil was disconnected. Game booted, no blown fuse. I’ll check each coil one at a time until it blows, then I should have the culprit. Super weird, though, because each coil tested good. Hmmm.

It was one of the rear kickout coils, AT-27-1300. As soon as those were plugged in, the fuse blew. When every other coil is plugged in except those, the game plays fine. Not sure which, but I’ll replace both.

I did a playfield swap last year and molexed the coils, and I’m glad I did. It certainly made troubleshooting much easier. I’m still not sure why the coil tested good with 11 ohms, but oh well.

Thanks, I didn’t know that.

If I hadn’t molexed the coils, how could I check that each coil had a good diode?

Good Lord! That’s a serious PSA to molex your coils.

Thanks for the input everyone. New coils on the way. I’ll update the thread once I install.

Nope, but my preference is to just install new coils and diodes. The AT-27-1300 coil has two diodes, and I’ve lived the nightmare of a coil with an incorrectly positioned diode.

It’s easier for me to just do a replacement on two 40 year old coils and diodes vs. new diodes on an old coil. Might be unnecessary, but I’ll feel better about it.

Hmm. I have an Alltek SDB. Good lights, nothing visually wrong (smoked transistor). I checked each transistor with my DMM, no issues.

If each transistor checks good with the DMM (one lead ground, one lead on the leg) and the board cycles normally, am I missing something on the SDB?

I’ll double check when I get home. When the game boots with a good 1 amp fuse, the green/blue inline drops function normally.

I ran through some tests before I disconnected the coils, and I didn’t notice any odd behavior during the lamp test.

Thanks again for the assistance! I don’t think it’s the SDB or solenoid expander, but I could be wrong.

New coils installed on the top and side eject.

With the top eject coil connected, the 1 amp fuse blows. No issues with the game when that coil is disconnected. The side eject coil works fine.

Q12 on the SDB tests normally with the DMM (ground lead on metal, positive lead on the transistor leg).

Based on my troubleshooting, I believe I have good a good coil, good diodes and a good board.

At this point, should I still be chasing a board issue, or is it more likely that one of the top eject coil wires may be frayed or touching something?
image (resized).jpg

Ha, no I appreciate it and I definitely read everyone’s suggestions. Tracing wires is not high on my want-to-do list, but I wanted to rule everything else out first.

Looks like I’ll need my flashlight and a free afternoon.

Lamp test does not trigger any coil response.

Top saucer coil:
4FCDE5CF-EA7E-46E9-B62D-F93C6B4DD39E (resized).jpeg
Right saucer coil:
83191252-D6AA-4454-882B-762665138D47 (resized).jpeg
J5 on the SDB:
ABAFAC58-F105-4C8E-8A5A-8A171088733D (resized).jpeg

Top inline drop target coils. The drop 1 coil *may* be suspect as the jumper wire between the first and second coil is exposed and may have grounded. Could this be a culprit?image (resized).jpg

Again, with the top saucer coil disconnected, the game operates perfectly. Once the coil is connected, the 1 amp fuse blows after about 3 seconds.

And I really appreciate everyone’s help.

The game has been rock solid for a year, so I suspect that’s not the case. Hopefully it’s something silly. Anyway, I’ll trace wires in the next few days.

I did a playfield swap last year. Original coils. No problems for about a year, now I’m getting the 1 amp fuse issue. Same issue after replacing both coils.

The sheathing only covered about 2/3 of the jumper. It’s possible it shifted over time and caused a short, but I can’t be certain. If the first drop target is tied to the back saucer coil, I thought they may be related.

I did not work on anything prior to the game having this issue. The game knew I was having a lot of people over for our kid’s graduation party and decided to die.

I was reading ~ 11 ohms between the two wired coil lugs during initial troubleshooting. I did not test them individually between the lug and ground, but I’ll do that and report back.

The diode polarity is correct on the old and new coils, but I’ll post pics.

Yes. If the back coil is plugged in, the game hums, and the fuse blows. The coils do not their thing.

If the back coil is disconnected, the game powers on normally. The coils do their thing.

DMM set to 2K ohms. Readings were too high for 200 ohms.

Top eject coil (black lead on ground):
Grey-red wire = 610
Orange wire = 630
Open lug = 640

Lower eject coil (black lead on ground):
Black-yellow wire = no reading
Grey-red wire = 610
Open lug = no reading

Resistance between lugs is ~13 ohms for both coils.

Other non-flipper coils were between 610-620.

Original coils I removed:image (resized).jpgimage (resized).jpg

Top eject coil:
744C12F5-D23F-4625-ADFC-9309EF082738 (resized).jpeg

Right eject coil:
406B2ED9-EF72-4795-8D94-083C570E122F (resized).jpeg

Molex connection on top coil (there is some blue overspray on the wires from the factory, but the wires are correct):
image (resized).jpg

Sorry, brown wire.

On the SDB, I’m getting no reading on each of the connections *except* Q12. This connection is reading 625. Board issue?

Red lead on Q12:
D2B4A747-F65A-431C-B0E2-05E6ADEDE022 (resized).jpeg

Red lead on other connections:
AFFA5AF9-44D5-4D9F-9821-36EA1AD5B72D (resized).jpeg

Edit: I just talked to Dave at Alltek. Sounds like it’s indeed a board issue. I’m curious why the transistor didn’t blow.

I was referring to the transistor, so I should have been more specific. The Q12 transistor was/is reading normal. I did not test the connector until today.

If you couldn’t already tell, I’m not the most proficient electrician. I’m having a bad day when I have to crack out the DMM. I learn each time, though.

Anyway, I already pulled the board and will send it back to Dave. I appreciate your help with pinpointing my issue. Thanks very much!

To close the loop, it was indeed the SDB. I swapped a working SDB in the game and it operates normally. The faulty SDB is on the way back to Alltek for repair. Nothing burned or smoked on the board, it still looks brand new. Rather than check just the transistor, I should have also checked the pin connector.

Thanks everyone for chiming in and being patient.