Some Key West Features Don't Enable

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Case Study Summary
Game Key West
Games Applicable To magic squares, but most other games similar
Source jeffrey lawton
Problem Reported all features except the magic squares and spot 2-18 don't ever enable
Fix not confirmed


Most of the machines have features that enable on a random basis during the spin cycle (playing coins/credits), and the features can be clumped into two categories:

  • things that enable independently
  • things that enable in sequence

Many of the independent features are implemented using trip relays. When machine decides to enable a feature, the trip relay trips. Switches in the trip relay light the backglass panel and connect the circuits needed to make the feature work.

Features that are sequence-dependent, like enabling shifting the numbers before 5th and after 5th ball shot, are normally handled by one or more stepper units. The sequence unit usually does the before 5th/after 5th/rollover enables, and things like enabling magic squares are handled by a different unit (cleverly calling something like the "magic square feature unit").


Key West - most of the feature enabling circuits

In this case, the magic squares were enabling, and so was the spot 2/18 feature. That means the power entering at the top on wire #75-5 from mixer #1 and the reflex unit was passing through a few switches and/or mixer #2 and reaching the point where the green and red circuits branch off.

The green circuit feeds into the spotting disc, and then down through the magic squares feature unit disc to a couple coils. One coil steps up the magic square feature unit to enable the ABCD squares, and the other coil is the spot 2 or 18 trip coil. This whole section of circuits was working ok...or at least appeared to be. It's possible that red circuit path into this area was dead, but occasionally the other path worked, so you just got the feature enable/advance less often than you should.

The part of the circuit not working is the chunk to the right that all feeds down into trip relays, and it must have the red circuit working or none of the trip relays will trip.


Note how the spot 2 or 18 circuit goes through both the red and yellow score discs. As the scores get higher, circuit paths are disconnected so it's less likely to get the spot feature enabled.

There is, however, a bypass circuit that goes around the score discs straight into mixer #3, so there's some chance to get the feature regardless of score levels.

Inspection Debug Procedure

There's very little in the circuit below the point that we know is ok. All that's needed is a check on:

  • CU cam switch 8
  • the spotting wiper fingers and spotting disc rivets
  • the slip ring wipers on the spotting disc hub to make sure they are in the right grooves

Just looking/cleaning/adjusting would probably fix the problem, but if you wanted to get a bit more technical, you could set up the spotting wipers in a position that should cause a trip relay to trip and manually close CU switch 8 (by lifting the stack with your finger). This technique is useful to check features that enable rarely, such as 2-in-blue on screen games, and it also lets you work your up backwards in the circuit with a voltmeter, so we'll look at that in the next section.

Voltmeter Debug Procedure

We know that the power to CU cam switch 8 is ok, but we don't know if the switch is operating properly. In any case, CU 8 is normally open when we are poking around. It only pulses closed briefly during the spin cycle.

You could just stick the CU 8 switch closed by misadjusting or jumpering it, but that could cause other circuits to be active when they shouldn't be and could lead to coils sticking on and burning or fuses blowing. If you're paying attention and check the schem for possible repercussions, the jumper wire is still a useful gadget.

The other approach is rambled about in the Electricity, voltmeters and reading a schem writeup, and relies on the fact that with switch CU 8 open, no current should be flowing in the trip relay circuits, so no voltage drop across the trip relay coils.

If you place one meter probe on wire #30 (which is where wire #75-5 eventually ties to if mixer 1 and reflex allow it) and the other probe anywhere down the schem from CU switch 8 when the spotting wipers are connecting the circuit, you'll measure 50V.

The trick is how to position the spotting wipers. One approach is to clip your meter lead onto wires #56-6 and #30 and then manually turn the spotting wipers backwards for a complete revolution. If you don't see 50V once in a while, there's a problem on the spotting disc.

Key West - section of spotting disc diagram

The more scientific approach requires looking at the spotting disc diagram and figuring out which rivets are important, then position the spotting wipers there and leave them there. Then probe around and find out why the 50V is gone.

In the diagram to the right, the red circuit is coming from wire #56-6 through a slip ring wiper to the search wiper hub, then down a wire to wiper C.

Wiper C is spinning around the 2nd ring from the outside, and occasionally running over rivets connected to the feature trip coils. One such rivet is at row 26 (the numbers go up in a counter-clockwise direction when looking at the wiper side of the board). If you turn the spotting wipers backwards to position wiper C on row 26, then you've set the spotting wipers in a position to tie wire #56-6 to wire #61-4, and you should measure 50V between wire #30 and wire #56-6.

You can poke around on the spotting disc by looking at where the wires attach in the manual. The diagram will show something like below, and in some games will even have the text labels on at the lug positions.

Key West - wire lugs on spotting disc diagram


Not reported back, but the likeliest problem was CU switch 8 not closing or the spotting slip ring wiper being in the wrong groove.