How to Tell if a Capacitor Is Bad

By Skip Shelton

Capacitors are used to store and release energy in a variety of electrical devices, including computers, flash bulbs, cameras, appliances, air conditioning units and other electrical systems. Degraded capacitor plates or insulators result in loss of peak energy storage capacity, stored energy leakage or complete loss of functionality.

Things You'll Need

  • Insulated wire
  • Insulated screwdriver
  • Multimeter

Step 1

Turn off the device. Remove any electrical plugs or batteries powering the device.

Step 2

Discharge the capacitor of any stored energy. Locate the two leads protruding from the sides or bottom of the capacitor. Close the circuit by touching an exposed wire across the two leads. Only hold the wire by the insulation-covered portion to avoid electric shock. If necessary, wrap the grip point of the wire with electrical tape. Use a screwdriver with an insulated handle for larger capacitors. Hold the wire or screwdriver across the leads for a minimum of 30 seconds to allow all the electricity to discharge.

Step 3

Set the multimeter to measure ohms. Press one of the multimeter leads to a capacitor lead. Press the other multimeter lead to the other capacitor lead. Monitor the resistance, measured in ohms, on the multimeter.

Step 4

Evaluate the capacitor's integrity. Good capacitors slowly store the charge from the multimeter battery.Good capacitors will initially read zero, then slowly increase to infinity. Shorted capacitors do not store charges and will read zero continuously on the multimeter. An "open" capacitor will not show any reading on the multimeter. Leaking capacitors will stabilize at a measure less than infinity.

Step 5

Replace shorted, open or leaking capacitors. Inspect good capacitors for bulging or leaks, which indicate failure of the physical components. Replace visually damaged capacitors.

Tips & Warnings

  • Multimeter readings indicating leaking capacitors should be verified against a known good capacitor. Some good capacitors will not read to infinity.