For electronic games it is always
best to work on the games with the power OFF. At the very least,
on games with a high power interrupt (many DMD style williams games and
late model Sterns) open the coin door to disable the high power.
The 50V power isn't likely to hurt you but it will do serious damage to
the circuit boards if you accidently put 50 volts on your 5 volt logic
or 12 volt switch circuits. And YES this happens to people a
LOT. Always use extreme cars not to cross any circuits when
working on a game powered on - your screwdriver or nut driver metal
shaft is really good at bridging circuits!
When cleaning a games playfield you can put the game in switch test
mode while you are cleaning. This allows you to clean and test
switches in one pass. Disable the high voltage if cleaning the
game with the power on.
Williams System 6 Flippers.
Gottlieb System 1