How to identify bad capacitors

Written by bailey richert
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How to identify bad capacitors
Capacitors can hold electrostatic charge. (capacitor image by naolin from

A capacitor is an electrical device capable of holding a charge, or energy, as an electrostatic field. Capacitors are made by separating two metal plates by a dielectric material, which is often an electrolytic liquid. The capacitor will have a greater ability to hold charge if the surface area of these plates is large. Capacitors are used in many common electronic devices, including computers. Faulty capacitors can result in problems with power and motherboard temperature. Replacing bad capacitors is required to repair the equipment.

Skill level:

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  1. 1

    Inspect the capacitor visually to see if any electrolytic liquid is flowing from the inside of the capacitor. A capacitor can only function if there is a dielectric material between the metal plates, and a capacitor is considered broken if this material leaks out.

  2. 2

    Look for swelling or disfigurement of the outside shell casing which holds the contents of the capacitor. This is an indication of electrolytic liquid expansion and thus indicates a bad capacitor. Look for a swollen top, denoted on most capacitors with a metal "X" shape.

  3. 3

    Place your finger on the top of a capacitor when the computer is turned off and cooled. Attempt to gently move the capacitor back and forth from its base. The capacitor should not move, remaining upright and sturdy. If the capacitor does move, it has been broken loose of its connection and is considered bad.

  4. 4

    Waft the air around the suspected capacitor to your nose, and smell. Try to identify the smell of ammonia, which indicates that electrolytic liquid from one of the capacitors has leaked out.

  5. 5

    Inspect all capacitors which seem to be functioning correctly to make sure that their base is parallel with the computer board. Though no dielectric material may be released, a non-secure connection between the board and the capacitor base will indicate a problem.

Tips and warnings

  • Do not touch a motherboard after it has been running. The metal will be hot and may burn your skin.

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