By Russ Jensen

Some time back, an article of mine appeared in The Coin Slot describing the history and characteristics of the so called "bingo" or "in-line" multiple coin pinball machines. These games are by far the most complex of any electro-mechanical game ever devised. The circuitry of these machines was evolved from that of the bingo's predecessor, the one-ball horse race machines, early versions of which had been around since the mid 'thirties. Later model bingos, however, were far more complex than their early ancestors.

Many of you who owned or operated one of these games, I am sure, have often wondered how these machines perform the functions they do. They even seem to have a mind of their own when it comes to giving you the extra advantages you seek with the deposit of additional coins. Also, the curious clicking sounds made by bingos, even after play is complete, seems mysterious to those uninitiated in bingo mechanics. This article will describe the important components of these fascinating games and briefly describe the major functions of each. No attempt will be made to delve into actual circuitry, although this type of information could be provided in future articles if enough reader interest is expressed.

The functions and components described will be typical of most Bally bingos made in the mid to late 'fifties. Bingos made by United (the other major manufacturer of these machines) and later model machines however, have similar circuitry, and the following discussion should apply, at least in general, to those machines also.


Before describing the actual components that make up a bingo Pinball, a description of the major functions that are implemented in one of these games seems to be in order. I have divided these functions into five categories; feature (and odds) selection, ball control, winner detection, payout, and extra ball feature.

Feature selection is the operation that occurs before the first ball is shot, during the depositing of one or more coins. For each coin deposited, or replay played off, various actions can occur. Odds may be increased, free numbers may be spotted, features such as four corners scoring or turning corners may be enabled, etc. These events occur in a pseudo-random fashion (described by the manufacturers as mystery Intervals) and it is entirely possible that nothing at all will occur (except for internal mechanism noise) with the deposit of any given coin. In many cases arrows on the backglass may advance to indicate to the player that certain features are getting closer to occurring.

Ball control includes raising the first, and subsequent, balls to the playfield, keeping track of which ball is being played, and allowing balls to be re-raised if one falls into the ball return hole at the bottom of the playfield.

Winner detection is searching the position in playfield holes. of all balls played to determine if a winning in-line (or four corners if enabled) combination has been achieved.

Payout is the scoring of replays, on the replay register on the backboard in accordance with the type of win (3-in-line 4-in-line, 5-in-line, or four corners) and the odds indicated on the backglass.

Finally, the extra ball feature allows a player the chance to play up to three extra balls, in addition to the normal five balls per game. These awards are achieved by depositing additional coins, or playing replays, after the normal five balls have been played. The awarding of extra balls also occurs in a pseudo-random manner as extra coins are played.


The heart of all bingo mechanisms is the control unit. This is a large motorized unit containing many groups of cam-operated switches and a large contact disk with rotating wipers at one end. This unit provides all basic timing functions to the game circuitry, as well as implementing the search for winning combinations. The unit is mounted horizontally on a shelf inside the backbox. A pictorial view of a typical unit is shown in the accompanying illustration.

The unit contains a motor, which continually operates, turning a shaft that extends the length of the unit. Attached to this shaft are many cams which operate sets of switches These cams are divided into groups, each of which (except for cam number 1) are clutch driven. The clutches are released, and thus the set of cams allowed to rotate, by the operation of solenoid coils called cam index coils.

Cam number one rotates all the time and provides basic timing pulses to the game's circuitry. Cams number 2 through number 9 are referred to as timer cams and rotate for one revolution each time a coin is de- posited or replay played off. The switches operated by these cams provide timing and control pulses, and signals required during feature selection and extra ball feature attempts. These cams, and their associated switches, are set into motion each time the timer cam's index coil, mounted directly beneath them, is energized. They then make one revolution and stop.

Cams number 10 through number 14 are called the replay cams and operate only during payout (awarding of replays). The switches operated by these cams provide all timing for the payout operation and are set into motion by the energizing of the replay cam's index coil. That solenoid is kept energized until the proper number of replays have been scored and thus these cams continue to operate during replay scoring. The adjustment of the switches associated with cam number 13 are critical to proper scoring of replays.

At one end of the control unit is a large disk studded with many circular rows of brass contacts. A set of switch wipers attached to the control unit's central shaft, is constantly rotating and making contact with the contact points in sequence. This disk is referred to as the search disk, and is the heart of the winner detection circuitry. Its wipers continue to rotate until a winner is detected, at which time they stop on that winner during payout.

After payout is complete they again start rotating, searching for possible additional winners. It should be noted that although the wipers on this unit are always rotating (except during payout) the rest of the winner detection circuitry is not enabled until the fourth ball is shot. This is the reason a bingo will never pay out until the fourth ball is in play, even though an in-line winner has already been made by the first three balls. During payout the rotation of the wipers is stopped by the energizing of the search index coil mounted next to the disk.


The other large motorized unit in bingos is the mixer and spotting unit. It is usually mounted near the top of the back door. Like the control unit, it has a motor rotating a central shaft and a large contact disk called the spotting disk with rotating wipers.

In addition to this large disk, four smaller disk units, referred to as mixers are mounted along the shaft. This unit could be called the "randomizer" of the game as it is essentially responsible for implementing the pseudo-random behavior of feature selection and extra ball awarding when coins are deposited by the player attempting to gain these game advantages.

This unit only operates when a coin Is deposited or a replay is played off, does its job, and then stops until another coin, or replay, is played. The spotting disk essentially elects which feature may be selected. When a coin is played, but the mixers many times will keep this feature selection from occurring. The mixers have an ingenious mechanical feature that causes each mixer disk to rotate a different amount each time it is set into motion.

The spotting of game advantages. as implemented by the mixer and spotting unit, works in conjunction with a small device called the reflex unit. This unit could be called the mind of the machine, as it makes the machine react to what has happened in the past. This unit looks like a small stepping switch with a metal box around part of it and has a set of small gears on the outside of the box. It Is part of the circuitry of the mixer and spotting unit and provides what is known as reflex play. In essence, this means that the more coins or replays a player plays without winning the easier the machine becomes in giving extra advantages such as features, higher odds, and extra balls. Conversely, however, the more replays a player wins the harder it becomes to obtain these same advantages. The circuitry of the mixer and spotting unit and the reflex unit combine to give the bingo pinball the appearance to the player of having a "mind of its own."

Historical note: Reflex and Mixer units were originally developed by Bally for use in the later model one-ball horserace machines. All of these games, starting with CHAMPION in 1949, contained reflex circuitry.


Working in conjunction with the search disk of the Control Unit to provide winner detection are five small relays called search relays.

The search disk sequentially scans all possible lines on the backglass bingo card(s). Each time a ball is detected in a hole corresponding to one of the five numbers on the card line being scanned, the search relay corresponding to that number's position in that line is energized. There is one relay for each position in a five number line. Three or more consecutive relays energized at the same time indicates a winning combination.

When this occurs circuitry connected with these relays causes the search index coil on the control unit to be energized, thus stopping the search disk wipers on the winner. The corresponding search relays are also held energized and provide information to the payout circuitry as to what type of winner (3-in-line 4-in-line, etc.) has occurred so that the proper payout can be made. Incidently, it is these relays closing and reopening every time a ball is detected during scan that causes that clicking sound characteristic of all bingos.

Prominently located on the inside of the back door of most bingos is a long bank of relays known as the trip bank. These relays correspond to game features that, once they occur, never happen again until the next game is started. Once one of these relays is tripped it can only be reset by a large solenoid(s), mounted at the end(s) of the bank, which is energized once at the start of each new game.

Game features such as four corners and ballyhole (a feature that when enabled, allows a ball in hole sixteen to do some special function) are controlled by trip bank relays. Another very important relay is called the selector lock. This relay is generally tripped when the fourth ball is shot. In fact, an astute player may hear the click of this relay being tripped as soon as the fourth ball leaves the runway. This relay has two main functions. First, it disables player controlled advantages (turning corners, spot number selection, etc.) that must normally be used before the fourth ball is shot. Secondly, it enables the winner detection and payout circuitry. This is why no bingo ever pays out until after the fourth ball is in play. This relay also enables the yellow button function, so that the player may try for extra balls. Feature hold-over functions, allowing a player to use some advantages after the fourth ball, can delay the functions of the selector lock until either after the fifth or sixth ball is shot. These features also have corresponding relays in the trip bank.

The trip bank also has a relay (most often two relays in tandem) called extra ball. This relay is tripped when the player pushes the yellow button on the front of the cabinet indicating he wishes to play for extra balls. After this relay is tripped any coins or replays played, until the red button is subsequently pushed, set into operation the circuitry that implements the extra ball function, either giving the player an extra ball to play or teasing him into playing more coins or replays in hopes of getting one the next time.

In addition to the trip bank and search relays, there is also a small group of relays in the backbox used to control other game functions. The Start relay operates any time a coin or replay is played and starts the timer cams on the control unit to initiate the feature selection sequence. Other relays control other game functions, such as the red button relay, which is operated when the player pushes the red button to start a new game after playing for extra balls.


The large backbox of bingo machines also contains a number of stepping switches that perform various functions. Most of these are mounted on the back door. One of these units, called the timer unit has two functions. First it acts as a ball counter indicating which of the first five balls has been raised to the playfield. The adept player may notice the sound of this unit being stepped up as each new ball of the normal five balls is raised. This unit controls the tripping of selector lock, and other ball in play sensitive features

The other function of this unit is that of play timer. After the fourth ball is shot, this unit begins to step up at regular intervals. When it reaches the top step, after quite some time, it causes the machine to tilt, thus terminating the game if the player leaves the machine without completing the game.

There are usually a number of stepping switches controlling various game features, such as spot number selection, A-B-C-D,turning corners, etc. These units are spasmodically advanced during feature selection (under the control of the spotting disk, the mixers, and the reflex unit) and enable the feature with which they are associated. The lighted teaser arrows on the backglass are also advanced by these units.

Two of the most important stepping units in a bingo are the score (or odds) units and the replay counter(s). Earlier bingos had one each of these units. Later models (those with three color independent odds) had three of each, one score unit and replay counter for each of the three colors; red, yellow, and green.

The score unit(s) is advanced pseudo-randomly during feature selection and control the odds lights on the backglass, which indicate the number of replays a player will receive if he completes a 3-in-line, 4-in-line, or 5-in-line winning combination on the bingo card(s). This unit, in conjunction with the corresponding replay counter, controls the number of replays awarded during payout.

The replay counter(s) controls the payout function. When a winner is detected by the search disk and search relays, the search disk stops and the search relay's contact circuitry indicates which type of winner (3, 4. or 5 in-line) has been found. The payout cams on the control unit are subsequently set into motion, and the pulse from one of these cam switches begins to advance the replay register (the three digit counter behind the backglass indicating to the player how many replays he has available).

At the same time, a replay counter begins to be stepped up by one of the payout cam switches. The replay counter may be stepped once for each, every other, or every fourth advance of the replay register. This is controlled by the position of the corresponding score unit (i.e. depending on the odds being paid out). This is done so that the replay counter will not be required to have a number of steps equal to the largest award (often 300 or 600 replays). The circuitry involved in stepping up this unit is a series circuit involving the score unit disk contacts and the disk contacts on the replay counter itself. When the proper number of replays have been awarded the replay counter's own disk contacts open the circuit and payout is terminated. The payout cams then stop, and the search disk again begins to search for another winning combination.

Note: The replay counter(s) is only reset at the start of a new game. This means that once a winner is paid off (say a 3-in-line for example) the replay counter remains at the step corresponding to that level of payout. If a larger winner (4 or 5 in-line) is subsequently detected, the counter will advance further until that level is reached. This results in the awarding of additional replays such that the total number of replays awarded equals the proper amount for the highest level of winner detected during the game. Later model bingos, having separate three color odds. have separate replay counters for each color, allowing three independent payouts.

All bingos having an extra ball feature have another stepping switch in the backbox called the extra ball unit. This stepper is advanced pseudo-randomly during extra ball (yellow button) play, the depositing of extra coins by a player attempting to obtain extra balls to play.

This unit has ten positions, the first being reached when the yellow button is first pressed indicating that the player wants to try for extra balls and lights the "extra balls" light on the backglass. The next nine positions light in turn, the other extra ball lights(first, extra, ball, etc.) The first two lights for each ball are teasers trying to tempt the player into trying again. When each extra ball is attained disk contacts on this unit, in conjunction with the trough switches in the ball trough beneath the playfield, control the raising of extra balls and their re-raising if one should fall into the ball return hole at the bottom of the playfield.

In addition to the typical units described above, many bingos have other specialized units in the backbox such as motorized units to operate moving screens and turning corners features. These units have electrical contacts, etc, in addition to the motor, to activate associated feature circuitry.


All but the very earliest bingos had most of their active circuitry located in the large backbox with a minimum of components in the main cabinet. This article is describing the major components used in the majority of these games. Very early bingos, however, (such as Bally's SPOT LITE from 1951) had their control units in the main cabinet.

All bingos have a shutter board mounted beneath the playfield. This board has two positions open, where all balls in playfield holes fall through and roll down into the ball trough beneath the lower part of the playfield and, closed, where balls in playfield holes operate switches that light the corresponding numbers of the backglass bingo card(s). This board is moved by a motor called the shutter motor, which also operates a series of cam operated switches.

The shutter is opened at the start of each new game when the first ball is raised, and then closed when that ball is shot onto the playfield when the second ball is raised. The period during which the shutter is open is the feature selection time during which the player may insert extra coins, or play off replays, attempting to enable game features and/or advance the odds. The cam switches on the shutter motor unit are used in conjunction with other game circuitry to enable or disable functions that should only occur during one of these two game periods - feature selection or actual play.

All bingo machines have automatic ball lifters; that is, a motorized unit that raises each ball up to playfield level, instead of using a manual ball lifter as in most other pingames of the same period. The ball lifter unit also has a cam that operates a set of switches. One of these switches insures that the motor makes one complete revolution each time a ball is raised. Another switch provides the pulse to step up the timer unit in the backbox, which keeps track of which of the five regular balls are in play.

Attached to the playfield is a relay, the lifter start relay, and two switches connected with the ball runway (the channel running from the ball shooter to the top of the playfield through which each ball passes when first shot by the player). These devices and the ball lifter unit described above, are the heart of the game's ball control function.

When a ball is raised to the playfield it comes to rest on a wire rollover type switch, the runway switch. This switch energizes the lifter start relay under the playfield. This relay disables the raising of another ball until the present ball is shot. Once the lifter start relay is energized, it is held on by a normally closed switch at the upper end of the runway, the ball gate switch. When the ball is shot, and leaves the runway, it pushes up on the ball gate switch, momentarily opening its contacts, thus dropping out the lifter start relay. Once that relay drops out it re-enables the ball lifter motor, and the next ball is raised to the runway.

Below the lower part of the playfield is the ball trough, the channel where balls end up when a new game is started, and roll down toward the ball lifter mechanism. This trough contains several rollover type switches, referred to as trough switches, which are involved with the ball control function.

The left most of these switches, trough switch eight, senses the fact, at the start of a new game, that all eight balls are in place in the trough. The raising of the first ball to the playfield is inhibited by this switch until all eight balls reach the trough. For this reason, if the first ball in a game is not raised, one should check to be sure that one of the balls is not stuck somewhere on the playfield or on the sloping board beneath it. The three switches near the right end of the trough, trough switches one, two, and three are used, in conjunction with the extra ball unit described earlier, to control the raising, and re-raising if necessary, of the three extra balls when one or more of these is awarded to the player during extra ball play.

This concludes the description of the typical basic components found in that fascinating device known as the bingo pinball. I am sure the reader can see from the above discussion that this type of game involves a highly complex and coordinated electro-mechanical system. As was stated earlier, the components described are typical of Bally bingos of the mid to late 'fifties, but the components of other bingos are quite similar in nature. As was also pointed out, this discussion did not involve actual circuit details.

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