What counts as an electro-mechanical (EM) game
EM games run on relays, switches and solenoids with no CPU, and were built from the 1930s until about 1978. Most from roughly 1960 on show the score on spinning numbered reels; games from about 1947 to 1960 usually light the point values on the backglass instead (1950s multi-player games, some 1953 Williams single players and some arcade games from about 1954 had reels earlier). The same repair methods apply to pinballs, bowlers, pitch and bats and gun games.
Systems
Related tips
Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part One, Clay Harrell (pinrepair.com)