How to Test Guitar Amp Capacitors

Written by skip shelton Google
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How to Test Guitar Amp Capacitors
Guitar amplifiers magnify sound through electrical circuitry. (Jupiterimages/ Images)

Guitar amplifiers magnify an incoming sound signal through speakers. Capacitors level the incoming electricity to reduce variance and enable high voltage discharge greater than the incoming electrical feed. Guitar amp capacitors charge by storing electrical energy on two plates separated by an insulator. Test your guitar amp capacitors with a multimeter to measure the resistance. Fully functional capacitors begin storing electricity from a discharged state until they are fully charged. Failed capacitors do not store electricity or leak the charge over time. Replace visibility damaged, bulging or leaking capacitors.

Skill level:

Things you need

  • Screwdriver with an insulated handle
  • Socket set
  • Socket wrench
  • Thick copper wire
  • Electrical tape
  • Screwdriver with an insulated handle
  • Multimeter

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  1. 1

    Switch off the guitar amp. Disconnect the electrical plug powering the amp. Use a screwdriver or socket wrench to loosen and remove any screws or bolts securing the amplifier cover to the housing. Remove the cover to access the electronics board. Locate the capacitor for testing and adjust the position of the amplifier housing to allow easy access.

  2. 2

    Inspect the capacitor for signs of failure. Burnt leads, bulges and dielectric gel leakage require capacitor replacement.

  3. 3

    Identify whether the two metal leads protruding from the capacitor are extending from the bottom of the capacitor or from both sides, one on each side.

  4. 4

    Discharge the capacitor. For capacitors with leads protruding from the bottom, grasp a metal screwdriver by the insulated plastic handle -- do not touch the metal during this process -- and touch the metal tip or shaft to both capacitor leads. For capacitors with leads protruding out each side of the capacitor, wrap a thick copper wire with electrical tape to provide an insulated grip. Bend the copper wire to allow both leads to be contacted simultaneously. Press the wire against the leads. Hold the screwdriver or wire against both leads for at least 30 seconds. The metal acts as a resistor and allows the capacitor to safely discharge.

  5. 5

    Adjust your multimeter tool to measure resistance or "ohms." The resistance setting is often indicated by the Greek letter "omega," which looks like an upside-down horseshoe.

  6. 6

    Touch the multimeter leads to the capacitor leads, one multimeter lead on each capacitor lead. Watch the multimeter resistance measure to determine the state of the capacitor. The multimeter leads have a small electric charge provided by the multimeter battery. Functional capacitors store this charge until the capacitor's electrical storage capacity is reached.

  7. 7

    Identify failing capacitors. Open capacitors fail to register any resistance. Capacitors failing to store any electrical charge read zero on the multimeter. Leaking capacitors initially show a measurement of zero and begin to climb stopping short of infinity. If you suspect a leaking capacitor, test a known good capacitor to validate expected behaviour.

  8. 8

    Replace failed capacitors.

Tips and warnings

  • Discharge the capacitor between tests for accurate results.
  • Do not touch the leads of the capacitor with your hands until you are certain the capacitor is discharged. Charged capacitors cause electric shock.

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