Could you post pics from under the playfield of the faulty slingshot?

Usually the power wiring to the coils is daisy-chained, so it hops from one coil to the next. It's possible there's just a break in the chain. I'd check for continuity from the slingshot coil to the other coils while looking for a loose power wire at any of them as well.

In the meantime I'll take a gander at the schematics and see if anything else pops out. Are all the other switches and coils working in the game?

Also, a link to the schematics for your game, free to download from The Internet Pinball Database: https://www.ipdb.org/files/2272/Bally_1986_Special_Force_Manual.pdf

Here's the relevant portion for the moment--it looks like there will be a red wire carrying the power to both slingshots and the 3 pop bumpers. That's the wire you want to make sure has continuity across all 5 of those coils.

Screenshot_20211202-184058.png

Excellent! Glad you found the culprit.

It's possible the over-active bumper could be triggering from it's activation switch being gapped too closely. Adjusting those switches can take a bit of trial and error to get them just right. You'll need to access the switch under the playfield. You want about a 1/16" gap between the contacts.

I will often test the pop bumpers I'm adjusting by (lightly) pounding the playfield a few times to see if I can get the bumpers to trigger without the ball.

Just out of an abundance of caution, when bombs are loaded and you hit the ramp, the pop bumpers will thump repeatedly to simulate an explosion. However, if this is happening at other times, then I agree with frunch to check the gap of the switch.

You can also test in switch test mode by banging on the playfield with your fist. If it signals then, then it is likely gapped too close. If it signals in switch test mode without doing anything, then it may be a bad cap on the bumper switch.

Excellent! Enjoy your game, that's a cool one!

Perhaps the switch for the capture hole is out of adjustment, or has a broken off wire or diode leg on the switch?

Do all the other switches on the playfield seem to work ok?

You're getting there, you'll have this thing 100% soon!

If the ball is stuck in that saucer, and you turn the machine off and turn it back on, does the ball eject? If not, then it certainly does sound like the switch.

You inspired me to play my Special Force today. Such a fun, underrated pin. I was on my way to a high score when my ball got stuck and I tilted trying to get it out. You’ll get yours working soon!

Also, keep in mind that there could be a broken wire on another switch in that same row or column that is affecting the saucer switch. So, if the saucer switch looks fine, time to start checking others that are connected.

That’s a solenoid expander relay. I’ve had cold solder joints on one that affected the kick out. Except I couldn’t even start a game. So check the solder joints and reflow if needed.

Also check for a lamp mounted under the playfield somewhere near that little relay board. The lamp should be an incandescent 555 bulb. Do you see that lamp come on when it's buzzing the relay on that board?

I should have mentioned that. OP, if you put the game in lamp test mode and have all lamps blink on and off, that 555 that frunch is referring to should also blink on and off, and the relay should make a nice clicking sound along with the blinking of the bulb. The 555 bulb needs to be working.

However, since it appears you can get a ball into the shooter lane at the beginning of the game, but not always later like when you capture a hostage, it does sound like it might be an intermittent problem with the relay. Cold solder joints can cause that.

Does the bulb light at all? In lamp test? If not, replace the bulb and see if that fixes things. You need a working bulb.

Was the game working once and then stopped or did you get it like this? Perhaps double check the wiring on the connector going to the board to make sure each wire is going to the correct pin.

If that looks good and if the relay buzzes but doesn’t click, it could be a bad relay. Marco Specialties used to sell replacement expander boards. Not too much money.

It sends power to one set of solenoids or another depending upon whether the relay is engaged.

https://nvram.weebly.com/bally-as-2518-66-sol-exp.html

This board splits the 43v solenoid bus into two lines. That way one one transistor can control two different coils depending on which way the relay is positioned. They use a lamp driver signal to control which direction the sol expander relay is directing the 43v bus.

The outhole, the rocket drops, and some other stuff should all make the sol expander relay click. It should click once right as the expanded coil fires.

4/5 problems with this board is related to cracked solder joints. It is mounted near the flippers which has experienced probably 100k shocks of the coil plunger slamming into nearby stop, single sided pcb without plated holes, etc... cracked solder joints.

I ran into this issue on my buddy's Black Belt a while back. If reflowing the solder on the solenoid expander doesn't fix it, it would also be worth re-seating the connectors on the mpu board in the backbox.

As I recall, I had reflowed the solenoid expander and still had no luck. Next, I pulled the mpu out to check the transistor for the solenoid expander, but everything looked/tested good. After putting the board back in, it's worked fine ever since. Only thing I really did in the process was pull the connectors off and put them back on when I reinstalled the board... so I chalked it up to a connector issue. It would probably be worth getting a look at the soldering for the header pins on the MPU, and reflow any suspect or cracked solder joints for them.

Not sure if you've found the solution yet, but I've been thinking over the problem. It looks like the Outhole Ejector (aka "Kick to Playfield" on schematic) shares the same circuit as the Knocker coil. It would be worth taking a look at both the Knocker and Outhole Ejector coils: check for proper wiring, and that the diodes on the coils have proper orientation etc.

Note that there's 2 coils in the ball trough where the balls go out of play--the Outhole coil that kicks the ball to the right--over to the Outhole Ejector coil. The Outhole Ejector feeds the ball to the shooter lane when activated (after a ball is lost and a new ball is started, or after a ball is captured)...That's the coil that's malfunctioning---and shares the circuit with the knocker coil.

Screenshot_20211208-203947.png

If everything looks good there, here's another question: does it only act up when the capture drop target is down? Or just when a ball is in the saucer? Odd thing is that the coil appears to be working unless certain game states are happening (if I'm interpreting the behavior correctly).

It may also be worth moving back a couple steps: exactly which wire needed to be reattached to get the slingshot working? Could you post a pic of the coil and the wire that was broken going to it?

I'm starting to wonder if that loose wire was disconnected for a reason (a fix to keep the game playing, despite some features not working)...

Btw--the knocker appears to be under the playfield near the left flipper, as far as I can tell.

Ok, hopefully we're getting closer to the culprit. Try putting the game in coil test with all the drop targets in the up position (including the single-drop targets like the capture target). With no targets down and no balls in the game, does the Outhole Ejector coil fire properly in the coil test? If so, try knocking down the capture target and see if the Outhole Ejector coil still fires. If it works, try placing a ball in the capture saucer and see if the Outhole Ejector still works.

I don't know if the capture target has to be down to put a ball in the saucer, but if it does--try raising the target back up while the ball is in the saucer and see if that corrects the issue. I'm guessing either the saucer or capture target is causing the mix-up for the Outhole Ejector, so this will hopefully help narrow down whether the problem's around there or somewhere else.

Another question: does the knocker work in coil test? Did you get a chance to check it out as per my last post?

We'll get to the bottom of this, just gonna take a bit more digging.

Nice! I don't like having no good explanation for a fix, but in a case like that I have to assume it's a bad connection. If it persists, you'll have to narrow down which connector is the culprit and reflow the header pins etc.

As far as the multiball issue: you want to make sure that all 3 switches in the ball trough under the apron (the cover over the ball trough/outhole area below the flippers) are ok. I know that's not where the balls are getting locked, but the game needs to know where the balls are between the capture/locks on the playfield and in the ball trough under the apron, otherwise it will assume it's still in play (afaik). Test with 3 balls, then remove 1, test again, remove another, test again. Experiment a bit, and see if you can get a ball to hang up in that area. I was reading that those switches can be difficult to get adjusted just right.

My theory is that the wire actuator for one or more of those switches may be preventing a single ball from rolling all the way down onto the switch it's supposed to be sitting on. With the weight of one or 2 more balls behind the "next" ball, there's enough force to push through the mis-adjusted switch actuators, but with just one ball it may not be quite enough on its own (and may hang out between 2 switches instead of resting on the one it's supposed to be on).

I'm thinking in this case, it's working fine as long as there's more than one ball in the Outhole Ejector trough--the weight of the extra ball or 2 is pushing the front ball into position, but once you've locked 2 balls--there's no extra weight to push the ball into the switch, so the game doesn't know the ball is there... So it's hopefully a matter of tweaking the switch actuator(s) just right so they allow the ball to roll all the way down without "help" from the other balls.

Again, that's just my guess at this point, but there appears to be some precedent for issues in that area.

You're getting close!!!

Btw, let me know if there's anything I can do to help verify you.

The switches you're referring to probably track a second and third ball in that area (the capture area to the right of the pop bumpers).

What I'm referring to is the switches under the apron all the way at the front of the playfield. There's 3 switches under there that also track the balls, and I think that might be where the problem is.

Basically, the game needs to be able to detect up to three balls at the Outhole Ejector trough, and up to three balls at the capture area (one in the saucer, and 2 behind it).

I would try setting up the game in the state you were describing (2 balls locked, one in Outhole Ejector trough, game stuck) and put the game into switch test. We want to see that the game recognizes all three balls correctly when it gets to that point.

I am thinking someone rewired coils or the 43v solenoid bus wire without taking care as to which side of the relay it should be on? Expanded coils have two diodes and three lugs. Without the diodes the voltage can feed through coil windings and then it would get interesting.

The manual should show what coils are expanded (three lug double diode). Schematic hard to read, but Page 44 of the PDF on IPDB. Top right box.

Capture DT and outhole same driver. Knocker and "kick to PF" same driver. Each one powered by different side of relay. Then the rest expanded drivers are a solenoid shared with flasher.

Hard to tell from the picture but "kicks ball to shooter lane" coil wiring looks suspicious. The third coil lug is just used for attaching the diodes (banded side), looks like I see an orange wire there.

Is the plastic melted around the diode body on the "saucer" coil? If so, that is a clue.

Have you checked the resistance on all the coils to ensure they are all within spec and no shorts?

You shouldn’t have to remove the coils. I recently accurately tested the resistance of all the coils on my Paragon, and I did it with everything connected. You may need to take care of which lug you put the two probes on to ensure you aren’t measuring through the diode but rather through the coil.

Whether you have to remove the diodes is a good question. I would think you would get zero resistance in one direction when current passes through the diode, and the coil resistance in the other direction. But I’m conceptualizing all this in my head, and it would be good for others to chime in.

Here’s a chart showing all coil resistances by part number:

https://www.flippers.com/coil-resistance.html