Under The Playfield
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. Here are 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.
BINGOS - FOR AMUSEMENT ONLY