I found this:-
"Spectrum is a 3 ball game with a codebreaker theme from Bally. It was designed by Claude Fernandez, and the art was done by Margaret Hudson. Claude also designed such games as Flash Gordon, Elektra, Baby Pac-Man, and Phantom of the Opera. It had a production run of 994 machines, with rumors of a significant number of machines never being sold (see rumors). It was a complex game that didn't perform particularly well on locations.
Spectrum was a unique game for several reasons. Although there were three balls installed, only a single ball was intended to be in play at any time. Secondly, no plunger is present on the machine. It is an Add-A-Ball machine, which was rarely used in the 1980s. There are no outlanes -- balls can only be drained between the flippers. Finally, the absence of a plunger will confuse most people at the beginning of their first few games."
Hope that helps a bit - confirms the three-ball bit. Maybe one of the kickouts has a faulty switch??
