I need to replace the coin door self-test switch on my US Tempest upright, and was somewhat confused when it looked like the simple SPST switch indicated in the schematics didn't match the original factory-installed 3-position SPDT on-off-on switch. Furthermore, there seemed to be some conflicting descriptions about flipping the test switch either up or down to active test mode.
After a bit more inspection I see that Atari wired the two outside SPDT switch terminals on my game together. One circuit wire goes to these, and the other wire to the common center terminal. The result is effectively a switch that is normally open in the center "off" position, and closed in either up or down "on" positions. So the switch can be toggled either up or down for test mode, and the center position used for normal game play.
This was probably obvious to folks with working switches, but now I can find an equivalent on-off-on SPDT switch replacement with confidence in knowing it was wired this way to cleverly allow testing in either up or down positions... or maybe to use up existing inventory of on-off-on switches when a simple SPST on-off switch would have sufficed.
After a bit more inspection I see that Atari wired the two outside SPDT switch terminals on my game together. One circuit wire goes to these, and the other wire to the common center terminal. The result is effectively a switch that is normally open in the center "off" position, and closed in either up or down "on" positions. So the switch can be toggled either up or down for test mode, and the center position used for normal game play.
This was probably obvious to folks with working switches, but now I can find an equivalent on-off-on SPDT switch replacement with confidence in knowing it was wired this way to cleverly allow testing in either up or down positions... or maybe to use up existing inventory of on-off-on switches when a simple SPST on-off switch would have sufficed.


