I am working on a Bally 6803, Party Animal specifically. I replaced the original corroded MPU with one that I acquired from a friend. This new board was nice and clean and worked great for about four or five games until EVERY coil in the game locked on and blew the playfield fuse. Replacing the fuse just blows it immediately upon power up because the game locks on every coil. I've tried the board in another game and the same thing happens.

And when I say every coil, I mean, all of the playfield coils except for the flippers. Even the flipper relay locks on right away.

I've replaced the 74154 decoder with no change. I've swapped out the PIA's and CPU chip with no change. At this point I'm thinking either ALL THREE CA3081's are blown or EVERY driver transistor is blown. Either of these scenarios seem pretty unlikely, so I'm coming here for advice before I start ripping more chips from the board.

The schematic is pretty clear that there's nothing else in the circuit (it's identical to the earlier SS Bally design), but something is forcing all of these transistors to ground as soon as power is applied. if it's not the 3081's or the transistors themselves, what could it be?

Any help you can offer would be greatly appreciated.

Here's a link to the Strange Science manual/schematic since the Party Animal schematic isn't on the IPDB:
https://www.ipdb.org/files/2396/Bally_1986_Strange_Science_English_Operating_Manual.pdf

Gah. Thanks for posting that. Not sure how I missed on the website.

Further to this, if I remove the transistor for any of the coils, the coil will not lock on. If I remove the CA3081 associated with the coil completely, the coil will still lock on immediately upon power up.

Totally lost. Anyone have any suggestions? The issue isn't the PIA because swapping them with different ones changes nothing. It's not the 74154 because the coils lock on even if it's removed. It's not the 3081 because the coils lock on even if they're removed. What else could this problem be? I figure it's a dead short somewhere on the board because the coils lock on immediately with power, whereas a data issue would presumably wait for the board to boot up, at least.

Testing shows that every driver transistor immediately shorts to solenoid ground upon power up. What would force the transistors to lock on without even the pre-driver 3081 being installed? The transistors that I've removed from the board all test good in diode test. I've even replaced a couple with no change.

Any help would be greatly appreciated. The schematic is posted above.

Using a logic probe, I've discovered that there is zero activity of any kind at the base of the transistors after I've removed the 3081's. The collector and emitter are both low held low.

Still digging...

Thanks for your message. I have replaced the 74154. Twice.

Thanks for this.

I have one 3081 removed, just for testing/comparing. The other two are still present. I've also removed a couple transistors, for comparing. Here's what I've discovered:
- The base of all transistors has no activity at all, regardless of whether the 3081 is present or not.
- The base of the transistor pads that I've removed is showing a high signal without the transistors present.

Further to this, the base of the transistors is actually hovering around 1.5v and is about 2v at the anode of the diode for each. This occurs whether the 3081's are on the board or not. Where the hell can they all be getting a signal from? I've replaced a few transistors with no change at all.

With the solenoid ground connector removed, I am able to see solenoid supply voltage at the collectors of the transistors. As soon as ground is added, the transistors all lock on immediately.

This one is literally keeping me up at night. I've memorized the damn schematic at this point. I hate to give up, but there has to be a reasonable explanation.

The major problem is that this is the 2nd board I've put into the game. When I first saw this machine, the MPU was not booting (it was badly corroded). I popped in another board and the game booted right up, but I realized that the playfield fuse was blown. Seeing no issues with the playfield coils, I replaced the fuse and all was well for several games before the coils locked on and things became a problem again. So now I'm petrified that even if I were to get another used board or even a Swemmer repro, I'm going to just blow that board up as well.

As a seasoned veteran of pinball repair (I've repaired hundreds of games for myself and dozens of other people for over 15 years), I'm not content to let this one win. But it sure is getting the best of me at this point. Any suggestions on where to go from here would be greatly appreciated.

THANK YOU for this. It was extremely helpful. It turns out that, as you discovered, removing a 3081 actually turns on all of the transistors associated with that chip, which, in turn, locks on the coils. After socketing and installing three new 3081's, I now have the game booting and no coils are locking on. It also turns out that you can't actually test the 3081's out of circuit... they have to be on the board for proper testing. i'm extremely grateful for the assistance thus far.

Now, can you suggest what would cause ALL THREE 3081's to die simultaneously? I've tested the ones I pulled and they are all pooched. I'm really hesitant to start playing the game until I figure out what caused this in the first place. But at least I'm one step in the right direction. Thank you again!

After some more inspection, I found that the power supply had one of its screws and plastic spacers missing and was subject to vibrations of the machine. I believe that the back of the power supply made contact with the ground plane and may have caused this issue. I reflowed some suspect connector solder joints on the power supply and replaced the spacer and made sure the power supply is tight and secure. I honestly don't know if these problems were the cause of the bigger issue, but I've played 20 games now and the machine seems to be playing like a champ.

Thanks again, very much, for the help and support.