Pinball Trouble-Shooting Part 3
By Russ Jensen
In the first article in this series on pinball troubleshooting we listed five areas of under- standing which were considered 'basic' to tracking down malfunctions in electro- mechanical games. The first two areas (the basic electrical circuit and schematic diagrams) were covered in that first article. In last month's article we began the discussion of the third area (pinball components) by discussing power sources and their associated wiring in the machine. This month we will continue the discussion of components by covering some of those which are the 'loads' in the basic circuit previously mentioned.
The 'loads' in pinball circuits are the components which utilize the electric current to provide some sort of' action;' not only action on the playfield, but also the operating of devices inside the machine that perform functions necessary to the game's operation. There are three basic types of loads in a game: lamps, coils, and motors.
I am sure that lamps are familiar to everyone so a detailed discussion of these is unnecessary. Lamps used in games are merely miniature incandescent light bulbs similar to the ones used in everyone's home except much smaller in size. When an electric current is applied to them they 'glow.' Lamps are used in games for illumination, score indication (in older games) and indication of certain conditions affecting the play of the game in the form of lighted panels on the back-glass, lighted bumpers or 'playfield inserts.
The load which does most of the 'work' in a game is the ‘coil’ or more properly 'electromagnet coil.' An electromagnet consists of many turns of thin wire wound around a hollow core ('bobbin'). When an electric current is pass- ed through this coil, a magnetic field is produced in the center of the core. There are three basic types of coils used in games. If the core is filled with iron, producing a solid core, the coil becomes a 'magnet coil' used in relays. If a small iron slug (commonly called a 'coil stop') is inserted in one end of the hollow core a 'solenoid' is produced. Solenoids are used in many pinball components such as flippers and stepping switches, as will be discussed shortly Finally, if nothing is inserted in the hollow core (other than a movable plunger) a 'bell coil' is produced.
In the case of the bell, when a current is applied to the bell coil, the movable iron plunger is repelled by the magnetic field produced by the coil and tries to 'shoot out of the coil.' The plunger strikes the bell's gong (which stops its movements) and falls back to its rest position when the current (and thus the magnetic field) is removed. The same principle applies to 'knockers' which are noise makers found in many games to signal the player that a free game has been won. In this case the gong is replaced by a wood block or metal 'stop' to produce the desired sound. The components which provide 'physical action' to the ball in play in most cases employ solenoids (with a 'coil stop') with a movable iron plunger placed partially inside the hollow core. When current is applied to the coil, the magnetic field produced causes the coil stop to become magnetized thus attracting the plunger toward it, stopping, of course, when they come in contact. The other end of the plunger is mechanically linked to the mechanism to which the motion of the plunger is transmitted. This can be the 'ball kicker* in a 'kickout hole,' a flipper, the 'kicker ring' on a 'pop bumper,' or the lever which strikes the stretched rubber ring in a 'rebound.' When the current is removed, the coil stop looses its magnetic attraction and the plunger returns to its original position, usually with the aid of some sort of ' return spring.'
The coil used for most flippers is somewhat different from other coils in that its winding is in two parts; a short winding which produces a large attractive force,, and a longer winding which produces a weaker field. When the flipper is' at rest' this latter winding is shorted out by a pair of electrical contacts which are part of the flipper assembly under the playfield. When the player pushes the flipper button all the current is applied to the other winding and the large magnetic force produced imparts a strong 'kick' to the ball. If this winding alone stayed energized for more than a second or two, it would get quite hot and eventually burn out. For this reason, as soon as the flipper has completed its forward action, the contacts in the flipper mechanism open (un-shorting the other part of the winding) allowing the current to pass through both parts of the winding 'in series.' This produces a weaker magnetic field, but sufficient enough to hold the flipper mechanism in its energized position. The cleaning and adjusting of these contact points are very critical and a frequent cause of flipper malfunctions^ If these contacts never open the 'strong' winding will soon burn out; if they never close extremely weak flipper action will result. Contact points (switches) will be discussed in greater detail in a subsequent article. The most common component in a game, other than the lamp, is the 'relay.' In its simplest form it consists of a 'magnet coil' (with a solid iron core), a hinged metal plate called an 'armature,' and sets of electrical switch contacts^ When current is applied to the coil, its core becomes magnetized, attracting the movable armature toward it. Attached to the armature is an 'actuator' made of an insulating material (usually containing horizontal slots) into which one blade of each set of contact switches is inserted. The movement of this actuator causes the contact points to either open or close depending on their configuration. Each relay can operate from one to several sets of switch contacts.
The purpose of relays is to allow the action of one electrical circuit to control one or more other circuits without an electrical connection between them. This even allows a circuit operating from one voltage to control another circuit which utilizes an entirely different voltage. Relays have a wide variety of uses in games and some specific applications will be discussed in subsequent articles.
The 'simple' relay just described will revert to its original state (due to spring tension on the armature) whenever the current to the coil is removed. There is however, another form of relay occasionally used in pingames which retains its state, due to mechanical latching of its armature, until a second coil (referred to as a ‘latch coil’) is energized. The first coil, incidentally, is called the 'trip coil.' These 'latch-trip' relays can easily be spotted by their two coil configuration and are primarily used as 'tilt’ or 'game over* relays in some later model machines.
Another relay configuration quite common in pingames is the 'relay bank,' sometimes called a 'trip bank' It consists of a number of relays (usually from 4 to 15 or 20) mounted on a common frame. Each relay has its own 'trip' coil, which acts in much the same manner as the 'trip coil' on the 'latch-trip' relay just described. When one of these coils is energized, its armature mechanically releases a metal plate connected to the actuator (which operates the relay contacts) which moves downward, thus opening and/or closing the switch contacts associated with that relay. When current is subsequently removed from the coil, the switch contacts will remain in their new position until the entire bank is later 'reset'
In the case of these relay banks, a method must be provided to later return all relays which have been ‘tripped' to their original condition. This is usually accomplished by a movable bar, running the entire length of the bank of relays, which can lift all of the contact actuator plates to their original position where they are again mechanically latched by the armatures returning (via spring tension) to their original positions. In older machines (generally before 1950) the resetting bar is moved (and thus the bank ‘reset’) mechanically as a result of the game being started when the coin chute is pushed in by the player. In most later machines, this resetting is accomplished by a large solenoid coil (commonly referred to as the 'bank reset coil and often operated by 110 volt power) the plunger of which is mechanically linked to the resetting bar. One exception to this is most later model Bally pingames which use a small electric motor to provide power to reset large banks of relays.
Relay banks are used where the conditions of several relays must be maintained until a specific event occurs such as the end of the game, the end of the ball in play, or the completion of a certain 'playfield objective' (i.e. the completion of a series of numbered bumpers). Some games have more than one relay bank, each being reset by a separate function. Relay banks are easily spotted by their common resetting bar and common mounting frame.
Next to the relay, probably the most common pinball component is the 'stepping switch.' It is in most cases the physically largest device in the game. It consists of a frame on which is mounted one or two (and in rare cases three) solenoid coils, a 'disc' made of insulating material and containing many metal 'contacts' (ar- ranged in a circular pattern), a rotatory contacting device, capable of completing electrical circuits with the contacts on the disc, and a ratchet mechanism to rotate the contacting device so it may make contact with successive disc contacts. The unit also has a number of solder terminals to provide connections for the many circuits it controls. Sometimes as many as 50 or more wires are connected to one stepping switch.
A common type of stepping switch found in games is the 'reset type.' It employs two solenoids normally referred to as the 'step-up coil' and the 'reset coil.' When current is applied to the step-up coil, its plunger
There are three basic types of loads in a game: lamps, coils, and motors. The load which does most of the 'work' in a game is the 'coil,' or more properly ‘electromagnet coil.' is pulled inward and causes the ratchet mechanism to rotate (advance) the contacting device to make contact with the next contact point(s) on the disc. Each sub- sequent 'impulse' applied to this coil advances the contactor to succeeding contacts on the disc until it finally reaches a mechanical 'stop' and can advance no further. When current is applied to the 'reset coil its plunger action causes the ratchet mechanism to be released The contacting device then quickly returns to its intial position ('zero position') due to a spring wound around its shaft which was 'wound up' with each upward 'step' of the unit.
These units have been widely used in games since the late thirties to advance score indicating lights. Each time the unit is stepped up, a circuit is completed (through the contacting device and the disc contacts) to light a different light indicating increasing score values on the backglass. In this manner the stepping switch 'counts' the number of score producing actions made by the ball in play. These units have also been used in later model games for a multitude of purposes such as 'ball counters,' 'advance units,' etc.
Another form of stepping switch is the 'continuous type.' It has only one coil, a 'step-up' coil. Its action is the same as just described for the 'reset type' with the following exceptions: 1) there is no 'stop' so the unit can be stepped completely around over and over again, and 2) since no 'reset is employed, there is no spring around the main shaft These units can easily be spotted because they have only one coil. (NOTE: A few pre-war machines employed 'reset type' stepping switches which had only one coil. They were mounted on the underside of the playfield and used the mechanical motion of the player pushing in the coin chute at the beginning of a game to actuate the resetting mechanism rather than using a 'reset coil.')
Continuous type stepping switches were used in applications where resetting was not necessary (i.e. 'match number1 units in games which included that feature). They were also widely used for the lowest value (i.e. 1000 or 10,000) score indicator light control in many games made between the end of World War II and the early sixties. In these applications, the game's circuitry provided a method of 'stepping' the switch around to 'zero' score when a new game was started.
A close cousin to the continuous stepping switch is the 'score reel' used to indicate the players' score on most later model (post 1960) games. These units can be considered as continuous stepping switches (in some cases without contact discs) which have 10 steps per revolution and with a rotatory disc attached displaying the numbers '0' through '9' through 'windows' on the backglass. Contact discs are employed on many of these units for 'number match' determination (on the lowest order digit) and for replay award determination (on higher order digits).
Most of these units employ three pairs of electrical contacts actuated by cams on the units main shaft One pair closes when '9' is indicated and is used to indicate a 'carry' so that the next higher digit can be incremented for proper counting. The second pair is closed at all times, except when '0' is indicated and is used to allow for resetting of that digit to '0' when the game is being 'reset to start a new game. The other contact pair either opens or closes at '0' (depending on the design of the game's resetting circuitry) and is used as part of the circuitry which determines when 'complete reset of all score reels has been accomplished. Malfunctions of these three contact sets are a major cause of malfunctions in games employing score reels, especially when a resetting problem appears.
Another type of stepping switch is the 'decrement’ unit. It is similar in appearance and operation to the 'reset type' with one exception. When the reset coil' is energized, the ratchet is released only momentarily allowing the unit to step backward one step (instead of going all the way to 'zero' as in the 'reset type' unit). These units are used in many games as 'bonus units’ which 'step up' when 'advance bonus' scoring devices are hit and 'step down' as the bonus score is being collected (added to the player's score).
A variation of the 'decrement' unit is the replay unit used to indicate 'free games’ on most machines made since the late forties. This unit has an 'indicator disc' (similar lot to those used on score reels) which displays the number for free game 'credits' through a window in the backglass. Each time a replay is awarded, the unit 'steps up' and each time a free game is 'played off the unit 'steps down' one step.
Another variation of the 'decrement type' stepping switch, found on a few machines, is a 'decrement type’ with a 'total reset.' These units have three coils, a ‘step up’ coil, a 'decremenf coil, and a 'reset coil. When the 'reset coil is energized, the unit resets to 'zero' in the same manner as the 'reset type' unit These units were mostly used as 'bonus units' with the 'total reset used at the start of a game. In some of these units to achieve a total reset both the 'decrement and the 'reset coils had to be energized simultaneously.
The ‘heart of any stepping switch is the contact disc and its associated contactor arrangement The disc is made of an electrical insulating material (usually bakelite) with metal 'contacts' embedded in it in a circular pattern. In most cases, there are two or more concentric circles of contacts on the disc. These contacts are usually in the form of brass rivets although some later model machines use copper 'printed circuit type contacts. Where rivets are employed, they are wired to the external solder lugs by small wires on the back of the disc. In many cases, several contacts are also wired together when the same circuit is to be energized at more than one 'step position' of the stepping switch.
The 'contactor' is generally in one of two forms. The most common type consists of one or more brass 'fingers' with a contact point at the end of each one. As the main shaft of the stepping switch is rotated (one 'step' at a time) these contact points make contact with the disc contacts in succession around the circle. The other form of contactor is a circular disc of insulating material with several 'spring loaded' contacts attached to it The rotation of the main shaft causes this disc to rotate, its contacts completing circuits in turn with the contact points on the stationary contact disc.
These stepping switch contact circuits are generally depicted on the schematic diagram as a rectangle containing a series of dots (representing the contacts on the stationary disc) and arrowheads (representing the movable contacts on the contactor).
In addition to the disc contacts, most stepping switches operate one or more sets of switch contacts of the type used on relays. Some of these switches may be operated by ‘pins' protruding from the ratchet wheel attached to the main shaft. These switches will normally be opened and/or closed by the stepping switch being reset' to its 'zero' position. In other cases, switches may be operated when the stepping unit reaches its 'top step' (in many cases these switches are used to open the circuit to the 'step up' coil when the stepping switch reaches its limit).
Many stepping switches (and score reels) also employ what are known as 'end of stroke' (abbreviated as E.O.S. on most schematics) switches. These switches are associated with one or both of the solenoids which operate the stepping unit when the solenoid's plunger is 'pulled in' (by current being applied to) these switches will be either opened or closed. They will then revert to their original condition when the current is removed from the coil. These end of stroke switches are often employed in circuits to assure that the solenoid has operated properly. An example of this type of circuit will be described in a subsequent article.