Bingo Glossary

Bingo Lingo
mystery intervals This was bally marketing speak for the idea that something may or may not happen when a credit is played or a coin is deposited.

The not-happening is what makes the games gambling devices in many jurisdictions. Generally, something would improve initially as each coin/credit was played, but as the scores/features got better, it became more likely that cycling the machine flashes the lights but nothing else happens.

S/I cards Score/Instruction cards. The score cards defined the payouts for 3,4, and 5-in-line/section, and the instruction cards gave minimal info on what the features did.

Many games also have a third/fourth card which explained unique features of the game, or indicated the OK game/red letter game guaranteed minimums.

spin cycle The spin cycle is when the game is eating your coins/credits as you attempt to impove the scores/features. "Spin" comes from the flashing lights that sequence around the backglass.
spotted A number being lit on the bingo card without a corresponding ball being it the hole. Usually spotting occured before the game started, but some games used the roll-over buttons to spot numbers.

About the most frustrating thing to do when playing a bingo is drop a ball in a hole that is already spotted, thus wasting the ball.

Machine Components
16 pulse cams

On most games, just to the left of the mixer motor on the top of the back door are the 16 pulse cams. These cams always turn when the mixer motor is running and toggle the switches above them. Whether the pulses generated by those switches make it to coils is determined by other switches, but when they do they are used for things like adding/removing more than one credit and running feature units to the top step.


also called a relay plate, it's the metal plate that gets sucked down into the coil top when the coil is powered. All sorts of things were attached or keyed to the armature to do something useful like moving switch blades, turning ratchets/cogs, releasing cams or kicking coins into the back of the cash box.

ball board

When the shutter panel opens and drops the balls, they land on the sloped ball board and roll down into the ball trough.

Some ball boards have wooden strips in various patterns to direct the balls.

ball gate

The one-way metal flap at the top of the ball runway which the ball passes under to enter the main playfield area.

Besides preventing the ball from re-entering the runway, there's a switch under the metal shell that triggers the lifter start relay to turn on the ball lift motor to raise another ball...unless you have one of the few games with a manual ball lift.

ball lifter

The mechanism used to raise the ball from beneath the playfield to the ball shooter tip.

A plunger below the ball shooter can be pushed in at any time to raise a ball for play.
A motor raises the ball when appropriate. On most games, a ball is raised as soon as the current ball leaves the ball gate. Some later games actually detect when a ball has fallen into a hole, and raise the next ball then.
ball lifter switch

at the bottom of the lift chute is a pin the ball waiting to be lifted sits on. The other end of the pin closes the ball lifter switch.

ball runway

The channel along the right side where the ball is launched up by the ball shooter to enter the main playfield area.

ball shooter

The spring loaded plunger with a rubber tip used to launch the ball into the playfield area.

The rubber tip should be replaced if torn, as pitted balls will damage the playfield quickly. The rubber tip and springs are cheap and and easy to get.

close at top/zero switch A pin switch that closes instead of opens. See open at top switch and open at zero/reset switch.
clutches/clutch washers/clutch plates

Any time there is a motor turning, but some things on the motor shaft need to be held still, a clutch is used. In this case, the clutch plate is a rotating metal disc keyed to the motor shaft - when the shaft turns, the clutch plate turns also.

Between the clutch plate and the thing you want to turn or hold still is an oil-impregnated leather washer. This washer is what slips. The surface between the washer and clutch plate and/or the washer and thing to turn may be the part that is slipping.

You're supposed to oil the washers with neatsfoot oil occasionally, but for limited use games occasionally = years. For games that have been sitting a long time, the clutch washers are often stuck and the only good solution is to disassemble the shaft to free and reoil them.

The pic shows a couple ok washers as well as some worn/damaged ones.

coin door

The front door that can be opened for access to the cash box. Early machines used a wooden door, while later games used metal.

The condition of this door can tell you a lot about how the game was operated. If the coin door has extra metal, locking bars, or gouges from attempts to pry it open, the machine has had a hard life.

coin guides

These trapezoidal metal bits attach to the bracket under the coin mech and direct the coins to the left so they properly operate the coin switch trip wire.

Usually the game had nickel guides installed and dime guides were stapled to the door in a plastic bag or screwed to the door as in the picture. You'd swap the coin mech and guides to change the machine to dime operation.

coin kicker

The coin kicker was a relay mounted on the coin door below the coin mech.

When a coin finished depressing the coin switch trip wire, it landed in a cradle and sat there until the relay coil was powered and the armature literally kicked the coin off the cradle into the cash box. See the picture under the coin guides entry.

coin mech

also known as coin acceptor, the mech did a decent purely mechanical job checking the weight, diameter and magnetic properties of whatever you dropped into the coin slot and decided whether it was a valid coin or a slug.

See the picture under the coin guides entry.

contact plate

Contact plates are found on units with rotating wipers. The plate itself is bakelite, and the contacts are either rivets or copper circuit traces.

drag arms

The drag arms are a couple of metal bars leaning up against cams on the front of the control unit. They periodically stop the cams from rotating, and in the process alter the positions of the cam lobes between themselves and the rest of the control unit. The net affect is to randomize the timing of certain events during the cycling of the game, such as the amount of time the spotting wipers turn.

In this pic, the arms are highlighted. The right arm is missing the drag arm stop. See drag arm stops.

fish paper

Fish paper is an insulating strip of a tough paper that is found in switch stacks. It prevents a switch blade from touching something conductive - like an adjacent switch blade or in this picture, the panel switch bar that is pushing multiple switch blades at the same time.

Fish paper is commonly wavy or curved, so it can look like it's a mangled switch. It's ok. All switches have contacts on them, fish paper and a few other types of blades found in switch stacks don't.

foot rail

Also called a lockdown bar, the foot rail is the wood or metal covered bar across the bottom of the game that holds in the playfield glass and often has feature control buttons/knobs on it.

index disk

See mixer rotor.

jones plug

The plugs/sockets used in bingos that connect parts of the machine together (e.g. playfield to head). Jones was the company that made them.

Some very late model bingos didn't use jones plugs. They used plastic amphenol connectors instead.

mixer rotor

Also called an index disk, a mixer rotor is a piece of the mixers assembly. It's the part with the wipers that spins when the mixer latch arms are pulled down so the latch pin disengages a notch on the rotor edge.

An unusual rotor has a conducting ring on it's non-wiper surface that a finger rides on. Afaik, it was only used on Miami Beach


Much more complex than the reflex unit, the mixers are a set of contact plates and rotors with wipers that are used to do "proportioning" during the current game.

From a players point of view, proportioning simply means that the higher your scores/features go, the less likely it is that the game will give you extra balls or increase the scores/features even more.

open at top switch

pin switch(s) that change state when a stepper/stepping unit is at its top step i.e. the position where the unit cannot phyisically step more because of the flat spot/missing teeth in the ratchet.

At the penultimate step (top step - 1), the pin may be touching the switch blades, but it must not push then far enough to affect the switch contacts.

It's common for a stepper unit to have switches that operate at-zero and at-top, and the switches are mounted on one stack. Almost always the ratchet has two pins - one pushes the stack one way at zero, and the other pushes the stack the opposite way at top step. If the at-top switch blade could touch an at-zero blade, there will be a piece of insulating fish paper between the blades.

open at zero/reset switch

pin switch(s) that change state when a stepper/stepping unit goes from the reset position (step 0) to step 1. The switches remain in the step 1 state for the rest of the steps of the unit. In the picture, there's three open-at-zero switches, but in general there can be zero or more switches and each can be open or close at zero. The key thing is each switch changes state when the unit steps up once from reset.

At step 1, the pin may be touching the switch blades (they aren't in the pictured unit), but it must not be pushing them far enough to affect the switch contacts.

Open-at-zero is the same as open-at-reset.

panel switches

The sliding board under the playfield that allows/prevents the balls from dropping through the holes is the shutter panel.

On most games, a metal bar is attached to the shutter panel and it pushes a set of switches when the shutter is closed. On the schematic, these switches are called "panel switches" or "shutter switches".

It's not unusual for the bar to loosen and not operate the switches correctly.

On some games, the panel switches are called shutter switches and you see things like "shutter sw. closed when open".

While this is probably a more correct term ("panel" was also used for the flip-down board in the head that had all the lamps on it), it's also confusing because the shutter motor cam switches were sometimes labelled something a bit shorter than that - like "shutter cam 3C" or "shutter motor 3C".

The almost always safe thing is to see if the switch is on the shutter cams by looking at the shutter motor diagram in the manual for a switch with the right wire id's/colors connected. If you don't find it there, and you aren't unfortunate enough to have a manual with a lot of errors or no shutter motor diagram, look on the bottom of the playfield at the panel switches.

pin switch

Generically, a switch that is operated by a pin sticking out of a (usually) rotating component like a cam or wiper.

The most common ones are open/close at top and open/close at zero/reset switches on the sides of a stepper/stepping unit, but the ones actually labeled with the word "pin" in the manual are typically switch stacks lifted by pins poking out of cams - like a search wiper pin switch.


A button on the foot rail with a single letter R on it. On most games, in order to search for wins, you need to push the R-button.

On games where you could rearrange winning combinations via things like the magic screen, you need to push the R-button for every winning combination you set. If you don't find all the possible winners before starting the next game...too bad!

The main reason for the R-button was to have more control over when scoring happened, and it had the nice side effect of reducing wear in the game, as the search disc wipers were held stationary until the R-button was pushed.

On earlier games where the search wipers were rotating constantly, the contacts on the search wipers and the armature on the search relays would wear.

On some later 6-card games with double-or-nothing, they used a C-button for the winner search. The R-button was pressed to take "regular" wins, or you could push a D-button to try for double.


A metal or plastic disk with teeth around the edge like a gear. The ratchet is usually attached to a shaft that rotates wipers, but it may also be used for things like counting credits on a replay counter.

rebound rubber

The rubber disk mounted at the top left of the playfield that the ball bounces off if you shoot the ball hard enough.

reflex unit

A simple mechanism in the game which stepped up when credits were won and stepped down when credits/coins were played.

As it stepped up/down, electrical circuits in the game were broken/made. The circuits were used when playing for scores/features or extra balls.

Bally marketing speak referred to the reflex unit as "proportioning the game". What that really mean is that as credits are awarded, the game is less likely to give you extra balls or increase the scores/features.

As credits are played off/coins deposited, the game gets more generous.
The reflex unit does not reset between games, so if you win big, leave the game and let someone else loosen it up with their money!

See reflex unit

replay counter

Usually a mechanical stepper/stepping unit inside the machine that keeps track of how many credits the player has been awarded for wins in the current game

In early games, there is one of these units and they had wipers and rivets. Most of the later machines use the printed circuit trace style of stepper as shown in the picture.

The unit ensures you are payed the appropriate amount for the currently detected win. If, for example, you win 12 credits for a 3-in-line, the counter will step up as the credits are added to the replay register. When the counter reaches the 12-level, payout stops. If you then pot another ball to give you a 4-in-line, the counter starts stepping up from where it left off until you reach the 4-in-line level.

Later games have multiple replay counters, so they can pay wins independently. For example, games with triple deck advancing odds/scores have three replay counters, one each for the red/yellow/green winners.

Another form of a reply counter is sometimes used for high payouts that don't have more than a couple stopping values, like blue scores 300/600. This unit just has a ratchet with a lot of teeth and a couple switches to detect the low and high pay amount.

see also: score disc/replay counter

replay register

The three or four digit unit that shows the player the number of credits they have. Not to be confused (much) with a replay counter.


See: mixer rotor.

runway switch

This switch is under the rollover wire in front of the ball shooter. When a ball depresses the rollover, the switch closes and on most games powers the lifter start relay.

On most games when the lifter start relay powers, ball lifting is prevented. If you power-on the game with balls in the trough and the playfield tipped up, often balls will start lifting repeatedly and dumping out into the cabinet near the 120V power switch. Not ideal. If that happens, close the runway switch with your finger to stop the ball lifting (after the current lift completes).

score disc

The score disc is a stepper unit that lights the odds lamps, determines payout amounts, and adjusts the odds of getting features.

As the scores advance, the chances of lighting additional features reduces.

see also: score disc/replay counter

scramble magnet

Not to be confused with a "scramble unit" used on some late-model 6-card games, the scramble magnet is a small coil attached to the control unit motor frame. It was used on a few early machines, and added more randomization to the spin cycling.

The main cycle randomization is done by the drag arms and drag arm cams. The drag arms pause the rotation of the timer cams, which lengthens the amount of time the spotting wipers and mixer rotors spin. The scramble magnet controls a metal arm that changes the drag arm cam behavior, again altering the duration of the timer cam rotation.

If the scramble magnet wasn't working, you'd almost certainly never notice.

search disc

A large contact plate and wiper assembly inside the game that is used to detect winning combinations. It works by controlling a set of five or more search relays. Some games have multiple search disks due to a larger number of cards or ways to win that need to be checked.

As the wipers spin and make connections, search relays power when balls are in the holes the wipers are checking. If the correct number of search relays are closed, the search stops and payout circuits are activated.

After payout completes, the search continues for more paying combinations, though an r-button press may be needed to search again.

Higher payouts can get broken into two pieces - payout for a 3-in-line, a pause, then the remainder of the payout for a 4-in-line or higher.

see also: search disc techno details.

search index

A search index assembly is mounted next to each search disk. It consists of a coil, some switches, and an arm.

In it's inactive state, the arm is lowered away from the search ratchet, and the search wipers are free to spin (unless held by something else).

When a winner is detected and payout is needed, the search index coil is activated and the arm engages a tooth on the search ratchet, causing the search wipers to stop on the winning contacts until the payout is complete.

The search index unit is also powered for more complex search functions, like counting the number of balls in a section to see if there's enough for a win.

On games with multiple search disks, there's multiple search index units.

search index lock magnet / coil

see: search lock magnet

search lock magnet

This thing releases the search wipers to scan for wins on games with an R button (or C button on late model 6-card games). When the wipers are locked, the red mark on the wiper finger more-or-less lines up with the red mark on the contact plate.

The locked wiper position is flexible on some games as the rivets around the locked position aren't connected to anything, but other machines need the wipers locked at position 0. In general:

  1. 6-card games - lock at position 0
  2. mystic line games - lock at position 0
  3. screen games - lock wipers between position 2-3. Anywhere from 1-1/2 to 3 is fine. Do NOT lock touching rivets at position 1 (the gerlitz video got this wrong).

Note the diagram in the manuals shows screen games with wipers at the 0 position. Oops.

search ratchet

A metal gear connected to the search wipers which the search index unit can engage to stop the search wipers from spinning.

search relays

The search relays are typically mounted on an upper edge of the back door, and are used in conjunction with the search disc to detect winning combinations of lit numbers.

It's the search relays that make all the clicking noises heard on the early bingo's. The amount of clicks increase as more balls are in playfield holes.

see also: search disc

search wiper lock magnet / coil

see: search lock magnet.

search wiper pin switch

When the search wipers are locked, the pin switch stack should be sitting lifted on top of a pin sticking out of the search wiper locking cam.

The switch position is adjustable to get it there.

shooter lane

see ball runway.

shutter cams

The cams attached to the shutter motor. Many of these cams are used during game reset when the shutter panel slides open.

shutter panel

A thin wooden board mounted to the bottom of the playfield. When slid away from the player, holes in the board would allow the balls to drop beneath the playfield onto another sloping board, which would direct the balls into the ball trough.

The shutter panel normally closes when the first ball opens the ball gate switch on a completely reset machine. Complete reset of the machine requires all balls to be in the ball trough, so if you power off a game with a ball in the ball runway, then power on and start a game, shooting the first ball will not close the shutter. Once all the balls are beneath the playfield, reset is complete and shooting the next ball will close the shutter.

shutter switches

Usually the switch stacks sitting on top of the shutter motor assembly underneath the playfield. See also panel switches.

slam tilt switch

Slam tilt switches are mounted to the cabinet, back door and/or coin door.

The weighted blade causes the switch to switch closed if the wood is whacked hard enough near the switch. When a slam tilt switch closes, the tilt trip relay is tripped and the game is over.

slip rings / slip ring wipers

Some of the wiper/contact plate assemblies like on the spotting and search units have wipers that spin in one direction only. Since they don't step up a limited number of times and reset like the wiper/contact plate assemblies on stepper units, it's not possible to connect wires to the wipers themselves - they'd twist up and tear off.

The solution is to use rigid wire wipers riding on the edge of copper discs in grooves on the unit wiper hub. This creates a little confusion in the terminology:

  1. wipers / unit wipers - e.g. search wipers - these are the ones that are running around the contact plate connecting to rivets.
  2. slip rings - the grooved channels on the above wiper hub assembly
  3. slip ring wipers - the rigid wires connecting the hub to wiring. These wipers should have a slight flex to apply pressure to the slip rings, but excessive pressure will wear the cupped section off the slip ring wiper a lot faster.

A coil of wire wound around a spool and a metal plunger partway inserted in it. Apply power to the coil and the plunger is sucked into the spool, pulling whatever is attached to it.

spotting disc/wipers

the metal wiper fingers rotate and make contact with the rivets on the spotting disc. The rivets that the wipers stop on are the first hurdle to overcome to get odds advancement, features lighting, or extra balls awarded. The mixers and feature/score units decide whether to ignore the spotting disc or not.

spotting index

The spotting index assembly is mounted on the back door just to the right of the spotting disk. It consists of a coil, some switches, and an arm. In it's inactive state, the arm is engaged in a tooth on the spotting ratchet, and it stops the spotting wipers from turning. When the coil is activated, the arm moves away and releases the spotting wipers so they can spin.

spotting ratchet

A ratchet connected to the spotting wipers which the spotting index can engage to stop the spotting wipers from turning.

stepper/stepping unit

lots of these in a machine. A contact plate with wiper fingers on one side that rotate when a coil causes a ratchet to move one tooth.

see stepping units

trough switches

the trough is where the balls roll down into after they are dumped below the playfield. Some rollover wires move these switches, and they are used to decide when to do things like disable moving numbers.

There is usually a metal plate screwed to the trough that covers the switches to protect them from the coin box.


Wipers are usually metal fingers with a contact on the end. They act like a rotating switch. You'll usually find them on:

Just to add a little confusion, there's also slip rings / slip ring wipers.