How Pinball Machines Work

The Backbox

The main controller board lies behind the backglass.
The main controller board lies behind the backglass.
Photo courtesy Martin Wiest

­The backbox portion of the table serves two purposes: to hold the main el­ectronics of the game and to attract players with a decorative piece of art located on the backglass. The electromechanical bumpers and flippers found on the table are all tied into the main controller board located behind the backglass. Located on this board, like on a computer motherboard, is a ROM chip that contains all the information needed to play the game.

The wiring that runs from the controller board to the rest of the machine is massive, usually consisting of over a half-mile (0.8 km) of wire. These wires carry commands back and forth between the main board and the flippers, bumpers, targets and ramps.

There are usually two other pieces of electronics contained in the backbox. A dot-matrix display board, usually either 128x32 or 192x64 pixels in dimension, is located at the base of the backglass. This display is used to relay information to the player, such as the score and hints about how to increase the score and possibly get a free game. Also, since the early 1990s, a speaker has been located on either side of the dot-matrix display. Pinball sounds are now digital and have grown to include full musical scores to accompany game play.

The backbox also has a second purpose: to attract players. The backglass art is carefully crafted to draw the player to a certain machine over any other in the arcade. Usually done by a professional artist, some original backglass paintings have been sold to collectors for thousands of dollars. Along with the art, the dot-matrix display is also used to attract players. Elaborate animations are created to run on the display in conjunction with the theme of the machine.