Mains power safety

⚠ Safety guide. This page covers hazards that can cause serious injury or death. Read it fully before you start, and if you're unsure, stop and ask someone experienced.

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! colspan="2" style="text-align:center;" | Guide details |- ! Topic | Safety |- ! Applies to | Both |- ! Difficulty | Medium |- ! How often | — |- ! Tools needed | Multimeter
Safety glasses
Replacement fuses (correct rating) |} "Mains" means wall power: about 120 volts in North America, 230 volts in much of the world. It can kill.

Where mains power is in a machine

• The power cord, line filter, power switch, and fuse holder
• The transformer and the input side of the power supply
• The monitor's power input
• Fluorescent lights and their ballasts (older machines)
• In older electromechanical pinball machines, wall power may run to many places: motors, relays, and lights

Rules

• Unplug the machine before touching any of these areas. See Before you open a machine.
• Check the power cord for cuts, cracks, or a missing ground pin. Replace a damaged cord; don't tape it.
• Never remove the ground pin or use a "cheater" adapter. The ground protects you if something shorts to the cabinet.
• Don't defeat interlock switches on coin doors or back doors unless you know exactly what they do.

Power supplies store energy

Modern "switching" power supplies have large capacitors on their input side that charge to roughly 170 volts DC (on 120 V power) and can hold that charge for a while after unplugging.

• Wait several minutes after unplugging before touching the power supply.
• Check with a multimeter (DC volts, across the large input capacitor) before working on it.

Fuses

• Always replace a fuse with the same rating and type. Check the amps, the voltage, and whether it's fast-blow or slow-blow.
• Never put in a bigger fuse, wrap a fuse in foil, or bridge it with wire. A fuse that keeps blowing is telling you something is wrong. Find the cause.

Pinball machines

Besides wall power, pinball machines have other high-voltage circuits:

• Displays: many solid-state machines run their score displays at 100 volts DC or more.
• Coils: flippers and other coils often run at around 50 volts or more and can give a nasty shock or burn.
• Treat the backbox and the area under the playfield as live whenever the machine is on.