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 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
     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
     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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