Techno Stuff
How They Work - Mixers

mixer shaft
magic ring
mixers and the mixer shaft

Almost all games have mixer discs and rotors that are normally mounted on the top of the back door. The mixers job is to help with game proportioning.

So what is proportioning? Basically, it's what statistically guarantees that the owner of the machine makes money.

If you'd played any bingo with advancing scores and lots of features, you know that for the first few coins/credits played the machine increases the odds and enables features almost every time. As the scores get higher, and more features enable, the usual result of spending your money is a bunch of flashing lights and nothing changes.

As the payoff increases, the game needs to insure that the costs of further improvements goes up. It does this by making it less likely for the various coils to get powered by using a very simple technique...it disconnects them. The disconnecting happens in a variety of ways. Sometimes a trip bank relay will trip to enable a feature, and when it does a circuit is disconnected by the relay switches. In other cases, the stepper units which are ratcheting up to enable features or determine the odds directly disconnects things. At the moment, however, we are interesting in how the mixers do their magic.

The early games had four mixers, and eventually a fifth was added :

  • mixer 1 works with the reflex disc to do overall game percentaging. Effects both score and feature advance (and extra balls).

  • mixer 2-4 are used for feedback. They use the enabled features to effect the score advance circuits, and the score levels to effect the feature advance circuits.

    Which mixer is doing which function varies from game type to game type. In general, the magic square games and beyond use mixer 2 to suppress score advance and mixer 3-4 to suppress feature advance.

  • mixer 5 showed up in the mystic line games, and primarily effects the score extra step circuits

Now the bad news...the mixers have a huge effect on the payout percentage of the machine. On most early games and a few later ones, it's possible for the operator to change this percentage by connecting/disconnecting jumper wires to unused solder lugs on the mixer discs. The problem is that Bally does not show the wiring diagrams for the mixers in the manual, and while the schematic shows what the mixer connects to, it doesn't provide enough detail either.

The solution apparently was to get copies of the mixer blueprints from Bally, or rumour has it that there was a document which told the operator how to change the percentages by hooking up the solder lugs on the mixers. I've never seen this document, but I do have a few copies of mixer blueprints.

If you plodded through the overhaul section, you may have seen that when I take mixers apart while working on games, I diagram the discs and post them. This is fairly easy to do, and since the same mixer wiring was used for many similar games, you may get lucky and find the blueprints for your machine or a similar machine.

How they operate

When the timer cams release, the mixer latch coil is powered to release the mixer rotors. The amount of time the mixer latch coil is powered is randomized by the drag arms and the mixer latch cams.

The drag arms delay the rotation of the timer cams, but eventually the cams revolve enough to remove power from the mixer latch coil. At this point, the mixer latch arms are free to be pulled up to engage the teeth around the edge of the mixer rotor and stop the mixer rotor in one of 24 positions.

Details on the drag arms and the mixer rotor release/engage mechanism are discussed in the common problems/parts that wear area.


overview | mixer 1 | mixer 2 | mixer 3 | mixer 4 | mixer 5