How to Check Capacitors

By Alex Cosby

Capacitors are a basic electronic component, used to store energy. They can be either electrolytic or non-electrolytic. Electrolytic capacitors are capable of storing much larger charges and are cylindrical components installed perpendicular to the PCB. Non-electrolytic capacitors do not store large charges, and are found in a variety of shapes, usually resembling a pill or a capsule.Like all electronics components, capacitors will eventually wear down and may fail. If you discover a faulty capacitor in your circuit, you will need to test all capacitors within that circuit to ensure they have not been damaged as well.

Things You'll Need

  • Screwdriver with insulated handle
  • Capacitor tester

Step 1

Check electrolytic capacitors for domed tops or crusty buildup. This is evidence of a leak, and no further testing is necessary: the capacitor needs to be replaced.

Step 2

Remove the capacitor in question from its position in the circuit, and discharge it by bridging its terminals with the metal rod of your screwdriver. You will need to be holding the screwdriver by the insulated end. If the capacitor is highly charged, it will spark and may arc-weld itself to the screwdriver.

Step 3

Turn on your capacitor tester, and set it to the appropriate resistance level. This number should match the resistance rating of the capacitor.

Step 4

Touch the probe terminals to each other to clear the reading on your capacitor tester.

Step 5

Record the reading on the tester, and connect the probes to the capacitor. The red, or positive, probe will be connected to the positive lead of the capacitor, and the black, or negative, probe will be connected to the negative lead of the same. Most capacitors will have a line on their jacket noting the negative side, and the positive lead should be longer than the negative.

Step 6

Observe the reading on your tester. For an analog tester, the needle should sway away from the infinity sign and then return. Failure to return to the infinity sign is a symptom of failure. If you are using a digital tester, verify the capacitance matches the rating of the capacitor. If it does not match the capacitance rating, it is failing.

Tips & Warnings

  • Bear in mind this does not test loss or noise on your circuit. These factors can have a significant effect on your capacitors.
  • Do not discharge a capacitor without insulation.
  • Capacitors have the capacity to store a fatal charge and should be handled with caution.