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How to Diagnose a Weak Capacitor

Capacitors are electronic components, usually cylinder or disc-shaped, that store electrical charge. Over time, they can deteriorate, making electronic equipment noisy and act erratically. A piece of test equipment called an ESR meter will diagnose weak capacitors. An ideal capacitor has only capacitance, but real capacitors have a combination of capacitance and an equivalent series resistance, or ESR. As the capacitor ages, the ESR may increase, reducing the current in the circuit and causing poor performance. If the ESR meter reveals weak capacitors in a circuit, replacing them may restore the equipment to its original performance.

Things You'll Need

Screwdriver with insulated handle
ESR meter

Instructions

- 1
  Discharge the capacitor by touching both of its terminals with the metal screwdriver blade.
- 2
  Turn the ESR meter on. Select a frequency rate that matches the capacitor's application. For example, use 100 Hz for a power supply and 1,000 Hz for a capacitor used in an audio circuit.
- 3
  Grasp the insulated plastic handles of the ESR meter's probes. Touch the metal tips of the probes to the capacitor leads. Measure as close to the capacitor body as possible; the capacitor's leads contribute a small amount of resistance. Electrolytic capacitors having values of 100 microfarads or more should have an ESR reading of a fraction of an ohm. Smaller capacitors may have resistances of a few ohms. If the meter reads an ESR greater than this, the capacitor is likely defective.

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