Bench testing guide
Multimeter fundamentals, then the exact test procedure for every component in the library.
Before you probe anything
Power off and unplug before changing connections. Discharge electrolytic capacitors (a resistor across the legs, never a screwdriver). Keep one hand in your pocket when probing anything above 50 V. Mains-side faults are for qualified technicians — full stop.
Multimeter fundamentals
Measuring voltage (V⎓ / V~)
- Probes across (in parallel with) the component — black to COM, red to VΩ.
- Pick DC (⎓) for batteries and boards, AC (~) for mains and transformers.
- Start at a range above what you expect; auto-ranging meters handle this for you.
- A reading with a minus sign just means the probes are swapped — the magnitude is right.
Measuring current (A)
- Current is measured in series — you must break the circuit and route it through the meter.
- Move the red probe to the mA/A socket first. This is the step everyone forgets.
- Start on the highest current range; the mA input is protected by a fuse you will eventually blow.
- Never connect the meter in current mode across a supply — that is a short circuit.
Measuring resistance (Ω)
- Power the circuit OFF and discharge capacitors first — resistance mode injects its own current.
- Lift at least one leg of the component out of circuit, or parallel paths will lie to you.
- Expect the marked value within tolerance: a 1 kΩ ±5% resistor may legitimately read 950–1050 Ω.
- OL / 1 means over-range or open — try a higher range before declaring it dead.
Continuity & diode test (🔊 / ▸|)
- Continuity beeps below a few tens of ohms — ideal for tracing wires, fuses and solder joints.
- Diode mode shows forward voltage: ~0.6–0.7 V silicon diode, ~0.2–0.3 V Schottky, 1.8–3.3 V LED (it may glow).
- A good diode conducts one way only; both ways = shorted, neither way = open.
- On transistors, base–emitter and base–collector each behave like a diode from the base.