Pinball Troubleshooting (PART 6)



By Russ Jensen


The article you are about to read is highly technical and may bore you to tears. If, however, a person who is truly interested in understanding pinball circuitry reads it carefully enough to grasp its concepts, the results will phenomenally increase his ability to troubleshoot malfunctioning games,

When this series of articles on Pinball Troubleshooting was started, five basic areas of understanding were listed that are required to perform successful fault isolation in a malfunctioning game. The first three of these (basic electrical circuit theory, reading of schematic diagrams, and basic game components) have been covered in the past five articles, although more on basic circuit theory will be presented this month. We are now ready to start talking about the fourth item on that list, types of circuit configurations commonly used in games.


Last month the many types and uses of switches were discussed in detail. Since the switch is the control element in the basic electric circuit, its connections in the game's circuitry are very important to understand. Before discussing switch circuits, however, some basic concepts and terminology should be clarified.

As you will recall, each switch in a game is mechanically actuated by some device (eg., relay armature, score motor cam, bumper, etc.). The actuating of a switch by one of these devices can be considered as an event occurring (relay energizing, cam follower dropping into a notch, ball striking a bumper, etc.).

In a previous article it was pointed out that each switch shown on a schematic will have a label next to it (relay name or letter symbol, solenoid name, etc.) that indicates which device actuates that switch. The switch is thus actuated when the event corresponding to that label occurs. For example: a switch labeled "TILT' would be actuated when the game's tilt relay is energized, in other words, that switch will be actuated when the event "TILT' occurs.

As we also learned last month, all switches will, at any time, be either open (no current can flow through them) or closed (current can flow). If an event, "A," causes a switch to close (a normally open switch actuated by event "A") we can call this switch's function **A" (current will flow only when event A occurs). If, on the other hand, we have a normally closed switch, also actuated by event 'A," its function is said to be NOT "A," Since it can pass current only when event "A" is not occurring.

The function of a switch (or group of switches connected in a certain configuration) can be defined as that event (or combination of events) which must occur (or not occur, in the case of normally closed switches) in order that the switch (or combination of switches) will pass electric current. This will become clear when examples of specific switch connections are discussed. Let me also point out that in the discussions to follow, I will use letters to signify events, but each letter can represent any switch actuated event occurring in a game (eg., bumper "1" being hit, score motor switch "1 A" closing, etc.).


There are two basic methods of connecting switches together, these are known as "series" and "parallel." Any complex connection of switches can be broken down into combinations of these basic connections. In "series" connections an external circuit wire is connected to one side of a switch, the other side of that same switch is connected to one side of a second switch. If only two switches are connected, the other side of the second switch is connected to another external circuit connection. More than two switches can be connected in series" by connecting switch to switch as described above, with the second external connection being connected to the last switch in the "series.'

In a "series" connection, in order for current to pass through the series of switches, all switches must be closed. This means that all normally open switches must be activated and all normally closed switches must not be activated.

An example of a two switch 'series" circuit is shown in Figure 3A. In this example, a normally open switch, activated by event "A" and a normally closed switch, activated by event "B," are connected in “series." It can easily be seen. that for current to flow through both switches, event 'A" must occur AND event "B" must not occur. The function of this series of switches (according to the definition presented earlier) would, therefore, be "A" AND NOT "B."

(NOTE: If more than two switches are connected in "series" their function would be the functions of each switch connected by AND. For example; three normally Open switches "A," "B," and "C," and one normally closed switch "D" connected in "series" would have the function "A" AND "B" AND "C" AND NOT D." This would seem reasonable, since for current to flow in a "series" circuit, the first switch AND all other switches must be closed.)

In "parallel" switch connections one external connection is connected to one side of every switch involved, with the second external connection being connected to the other side of all switches. In this type of connection, current can pass between the two external connecting wires when at least one of the switches connected in "parallel" is closed. It should be noted that more than one switch being closed will have no additional effect

Figure 3B illustrates an example of two switches connected in "parallel." In that example it can be seen that current will pass if normally closed switch "B" is not activated 0R if normally open switch "A" is activated. The function of these switches would, therefore, be "A" OR NOT"B." In other words, current will pass any time either event "A" has occurred OR event "B" has not occurred.

(NOTE If more than two switches are connected in "parallel," their function would be the functions of each switch connected by OR. For example: two normally open switches ("A" and "B") and one normally closed switch ("C") connected in "parallel" would appear to be reasonable, since for current to flow in a "parallel" circuit any one switch need only be closed.)

We have now seen that any single switch has a function equal to its actuating event if normally open, or NOT its activating event if normally closed. We have further discovered that when two or more switches are connected in "series" or in "parallel" the function of the combination of switches is the function of each individual switch connected by the logical connector AND or OR respectively. What this means is that a "series" or "parallel combination of switches can be considered to be equivalent to a single big switch, which will pass current only when its function occurs

The concept of the big switch can be carried one step further by connecting groups of "series" or "parallel connected switches in "series" or "parallel" with each other. The result would be equivalent to a big switch whose function would be the functions of each switch or group of switches connected by either AND or OR for "series" or "parallel" connections respectively.

To illustrate this idea, Figure 3C shows a combination of switches connected in both "series" and "parallel." A little study will show that for current to flow between the two external wires the following events must occur (or not occur, as the case may be): "A" must occur AND "B" must not occur AND either "D" must not occur OR "C" must occur. You can see that switches "C" and "D" are connected in "parallel" and these in turn are connected in "series" with "A" and "B" the function of this total combination is therefore: "A" AND NOT B" AND ("C" OR NOT "D").

(NOTE: The parenthesis in the function just cited is used as a grouping symbol indicating that the function contained in the parenthesis must be evaluated first before combining it with the other parts of the overall function. Had the parenthesis not been used the function could have been misinterpreted to mean that normally closed switch "D" was in "parallel" with the entire combination of switches A," "B," and "C" (instead of only with switch "C").)

In effect, the operation of every toad (lamp, coil or motor) in a game is controlled by either a single switch or a group of switches (which can be considered as a big switch having a complex function as described above). Remember, the load can only operate when its associated switch (simple or complex) is closed (allowing current to flow through it). The function of each load's switch (simple or complex) represents the conditions (events) required to energize that load.

In the proceeding examples, letters have been used to represent switch actuating events. When these letters are replaced by the names of actual devices in a game (such as "TILT," "GAME OVER," " 10 POINT RELAY," etc.) the functions which control a particular load begin to make sense and can relate to actual game operations. This will become clearer when actual circuits are discussed.

The switching circuit concepts just presented may seem a little difficult to grasp at first, but a little study should reveal that they are quite logical and actually relatively simple, when once understood Once a person understands these concepts, however, his ability to diagnose problems in a malfunctioning game will increase many fold.

Before leaving the subject of switching circuits one more point should be made. Some switches (normally those controlling the common power lines to different portions of the game) can be, in effect, in "series" with many of the games operating circuits. When analyzing one of these circuits, these common switches should be considered as if they were part of the function of each load that they affect.

This will be described and more circuit theory will be explained when Puss Jensen continues this very informative article in the August issue of The Coin Slot Learn how to troubleshoot for switch malfunctions and several tests to perform to isolate the various conditions in a game that cause unwanted problems.

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