Using a multimeter

Guide details
Topic	Skill
Applies to	Both
Difficulty	Easy
How often	—
Tools needed	Digital multimeter

A multimeter is the most important tool for repairs. It measures voltage, resistance, and continuity (whether two points are connected).

Choosing a meter

A basic digital meter is fine to start. Look for:

• Auto-ranging (it picks the scale for you)
• A continuity beeper
• A safety rating of CAT II or higher if you'll measure wall voltage

The main settings

Setting	Symbol	Used for
DC volts	V with a straight line	Power supply outputs, logic voltages, batteries
AC volts	V with a wavy line	Wall power, transformer outputs
Resistance	Ω	Checking resistors, coils, fuses (power off)
Continuity	speaker or sound symbol	Finding broken wires and bad connections (power off)
Diode test	diode symbol	Checking diodes and transistors (power off)

Rules

• Black probe goes in the COM jack. Red probe goes in the V/Ω jack for almost everything.
• Measure resistance and continuity only with the power off. Measuring them on a live circuit can damage the meter and gives wrong readings.
• Don't use the current (A or mA) setting unless you know what you're doing. Putting the probes across a voltage in current mode can blow the meter's fuse or worse.
• Keep fingers behind the probe guards.

Example: checking an arcade power supply

Most arcade game boards need very close to 5 volts DC. Too low causes resets and glitches; too high can damage the board.

1. Set the meter to DC volts.
2. With the machine on, put the black probe on a ground (GND) point and the red probe on a +5V point, measured at the game board, not just at the power supply.
3. You want roughly 5.0–5.1 volts. Many power supplies have a small adjustment screw to fine-tune it.

Example: checking a fuse

1. Unplug the machine and remove the fuse.
2. Set the meter to continuity.
3. Touch a probe to each end of the fuse. A beep means the fuse is good. No beep means it's blown.