⚡ Capacitor Testing Cheat Sheet

Quick reference — print-friendly

👁️ Visual Inspection

Bad	Good
Bulging / domed top	Flat top
Leaking brown crusty stuff	Clean base and vents
Cracked casing	Intact casing
Rust on legs or base	Clean leads
Scorch marks on PCB	No burn marks
Relief vent blown open (X or Y mark)	Vent scored but closed

🛡️ Safe Discharge

Capacitor Type	Method
Motor start/run (large, standalone)	Insulated screwdriver across terminals
Power supply electrolytic (on PCB)	1-10kΩ resistor or 12V bulb across legs
Small ceramic/film (on PCB)	Usually self-discharges; verify with multimeter

Verify: Set multimeter to DC Volts. Should read <5V.

📏 Multimeter Tests

Capacitance Mode (µF)

Set to capacitance (µF) range
Discharge cap first
Connect probes (red → +, black → – for electrolytic)
Should read within ±10-20% of rated value
Reads 0 = shorted. Reads OL = open. Low reading = dried out

Resistance / Continuity Mode

Set to ohms (Ω) or continuity (beeper)
Watch reading climb as cap charges (normal)
Stays at zero (beeps continuously) = shorted
Stays at OL immediately = open

🔢 Common Capacitor Markings

Marking	Value	Type
104	0.1 µF	Ceramic
103	0.01 µF	Ceramic
222	2200 pF / 0.0022 µF	Ceramic
470µF 25V	470 microfarads, 25 volts	Electrolytic
10µF 400V	10 microfarads, 400 volts	Motor run

💰 Typical Prices

Small electrolytic (10-100µF): $1-3
Medium electrolytic (470-2200µF): $2-5
Motor start cap: $8-15
Motor run cap: $10-20

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