By Russ Jensen

Sometime ago one of your readers suggested that I devote an article or so to pinball repair and troubleshooting. Since troubleshooting of pingames is one of my favorite pastimes (next to pinball history research, of course) I have decided to do just that. This will be the first of several articles dealing with basic pinball circuitry and fundamental troubleshooting techniques.

In order to be able to track down and locate faults in a pingame's intricate wiring, an understanding of the following is required: 1) Basic electrical circuit theory, 2) The method of depicting pinball circuitry on a schematic diagram, 3) The basic circuit components employed in a pingame, 4) The types of circuit configurations used, and 5) A systematic method of fault localization using simple' test equipment. These articles will try to cover (at least in a superficial manner) these areas.

First, however, let me begin with a few introductory remarks regarding the scope of these articles. This discussion applies only to "electro-mechanical" games, and while I talk about "pinballs" much of the discussion could only apply equally well to other electro-mechanical coin machines such as "baseball machines," "shooting galleries" (and other arcade devices), and also to many "console slot machines" which use relay and stepping switch circuits. Secondly, this discussion applies in general to cases where one has available the manufacturers' schematic diagram for the particular machine. If you don't have one, your job is a lot harder but the basic principles discussed here should aid you greatly in trying to figure out "what is going on" in your machine.

Now to the basics! The fundamental electrical circuit consists of three parts; the 'power source,' the 'switch,' and the 'load,' each of which will be discussed in more detail. These items are connected in "series," that is, for an electrical current to pass through any one of them it must also pass through the other two. The circuit is said to have two conditions, or "states." The "open state" is when the "switch" is "open" and under this condition no current flows through the circuit and consequently nothing happens. The other condition is the "closed state" which occurs when the "switch" is "closed." In this state an electric current will flow from the power source, through the "switch," through the load causing something to happen, such as a light lighting, a relay energizing, a motor turning, etc. It should be noted that the term "switch" used above actually can be a simple switch or a combination of switches as will be discussed later. The important thing to remember is that the circuitry of an entire pinball machine can be considered as a group of many of the simple series circuits just described.

Schematic Diagrams

The fact that a game can be considered to be a group of individual series circuits is aptly demonstrated by the manufacturers' depiction of the circuitry on the schematic circuit diagram for the machine. First a word of caution; there is another form of diagram used with some machines (mostly older ones) called a "wiring diagram." This type of diagram bears little resemblance to the schematic diagrams being discussed here as it traces the physical wiring rather than the individual circuits. So if you have this type of diagram you may almost entirely disregard the following discussion of schematics.

The format of most schematics is similar and usually has the following characteristics: 1) The power source(s), usually transformer windings (more about that shortly), are shown on the left side with their outputs shown as horizontal lines extending the length of the diagram, 2) The "loads" are shown, usually in a row from left to right, with one side of each connected to one of the power source lines (power common line’) and, 3) The "switch" associated with each load is shown below that load with the "switches" other side connected to the other power source line (“return line”) Each load and the "switch" (which remember is generally a combination of switches) connected to it can be considered a separate series circuit as was stated earlier. Since pingames generally have lamps and coils operated from different voltages, these two types of loads will be shown separately, usually one above the other on the schematic, each with its own power source and power connection lines. The symbols generally used on most schematics are illustrated in Figure 1.

In order to better under understand schematics some additional points should be discussed. Each coil (relay, solenoid, stepping switch coil, etc.) will have a 'name' (or in some cases a 'code letter') associated with it. If a 'code letter* is used. the schematic will usually have a table giving the 'name' associated with each 'code letter.' This 'name' (or letter) will be shown next to the coil symbol on the schematic and also next to the depiction of any other items associated with that coil, such as relay contacts. It should be noted that the contacts for a given relay, even though physically located next to each other in the game, may be widely separated on the schematic because each contact will be shown near the load it controls, but more on relays later. This is a major difference between a schematic and a wiring diagram on which all contacts would be shown adjacent to the relay coil.

Another piece of information found on the schematic, which is of utmost importance during troubleshooting, is the wire "color code." Each wire in a game has one or two identifying colors associated with it. The wires insulation has a "base color" and in many cases a secondary or "tracer" color. In a few cases the wires two colors appear in a one-to-one ratio on the wire; these are known as "mottled" colors. The color (or colors) of each wire depicted on a schematic is indicated next to the line depicting the wire, either by words (ex: Yellow-Red), by abbreviations (ex: YL-RD) or by "code numbers" (ex: 76). When "code numbers" are used, reference must be made to a table somewhere on the drawing which cross-references each number to a color, a situation which is sometimes very frustrating and time consuming for the troubleshooter. When code numbers are used the first digit indicates the "base color" and the second digit the "tracer" color(a0 indicates no tracer). The color code for "mottled" wires uses an ampersand (&) rather than a dash between colors (ex: YL & RD). It should be noted here that the same wire color(s) is used for any wires which are electrically tied together with no intervening "switch" or load, even though many branches may occur. As soon as a circuit encounters a switch contact or load (lamp, coil, etc.) the wire color changes on the opposite side of that circuit element. Circuits which pass through connectors (such as those used for electrically connecting the playfield to the backbox), however, retain the same color on both sides of that connection. These connectors, by the way, will very seldom even be indicated on schematics but will on wiring diagrams.

We have now covered the first two items on our list of areas which must be understood to enable one to troubleshoot a pinball machine. Additional information in these areas, however, will be found in the discussions to follow. Next month we shall begin with a description of the basic circuit elements in a pingame and continue from there.

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