How do I test if a component is bad (without fancy equipment)?

Short Answer: Use a multimeter in resistance, continuity, or diode mode. Most common failures are shorts, opens, or out-of-spec values.

Detailed: Here's how to test each component type with just a basic multimeter.

Step	What to do	Good result	Bad result
1	Set meter to resistance (Ω)
2	Measure across leads	Within tolerance (±5%, ±10%)	OL (open), 0Ω (short), or far off value

Note: You must remove resistors from circuit to test accurately — other paths affect reading.

Step	What to do	Good result	Bad result
1	Set meter to resistance (high range, e.g., 200kΩ)
2	Connect probes across capacitor (observe polarity)	Reading starts low, climbs to OL	Stays at 0Ω (shorted) or OL (open)
3	Visual inspection	Smooth top, no leakage	Bulging top, brown crust (leaking)

Capacitance mode (if available): Measure directly. Bad caps will read far below labeled value (e.g., 1000µF reads 200µF).

Step	What to do	Good result	Bad result
1	Set meter to diode mode (→┴ symbol)
2	Probe forward (anode +, cathode -)	0.6–0.7V (silicon), 0.2–0.4V (Schottky)	0V (short) or OL (open)
3	Probe reverse (cathode +, anode -)	OL (no reading)	0V (short) or any reading (leaky)

Step	What to do	Good result
1	Set meter to diode mode
2	Base (+) to Emitter (-)	0.6–0.7V
3	Base (+) to Collector (-)	0.6–0.7V
4	Emitter to Collector (either polarity)	OL (no connection)

If any of these are shorted (0V) or open (OL when should conduct), the transistor is bad.

Step	What to do	Good result	Bad result
1	Set meter to low resistance range
2	Measure across leads	Low resistance (0.1–50Ω typical)	OL (open winding)

Inductors rarely short, but they often go open (broken wire).

Step	What to do	Good result	Bad result
1	Set meter to continuity (beep mode)
2	Probe both ends of fuse	Beep (continuity)	No beep (blown)

Pro tip: Many "dead" devices are just blown fuses. Check the fuse first.

Garage Circuits