How to Test Bridge Rectifiers and Zener Diodes

Written by robert osborne
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Bridge rectifiers and zener diodes are commonly used in electronic products such as computers and stereos. Bridge rectifiers are composed of a four-diode array. These diodes convert alternating current into direct current. Bridge rectifiers have four leads, and are found in power supplies. Zener diodes are used to provide regulated voltage for power supplies. A failure of either a bridge rectifier or zener diode prevents electronic devices from working properly.

Skill level:

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Things you need

  • Digital multimeter

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    Bridge Rectifier

  1. 1

    Unplug the device that contains the bridge rectifier. This ensures the bridge rectifier is without power.

  2. 2

    Set the digital multimeter, or DMM, to the "diode test" setting per the device's instructions.

  3. 3

    Test the bridge rectifier diodes. Place the DMM's two leads on two adjacent rectifier pins. The DMM will read either "OL," indicating an open circuit; or a voltage of 0.7 volts DC or less. Switch the DMM leads. An operational bridge rectifier diode shows a reading opposite of the previous reading. Perform this test on each adjacent pair of bridge rectifier pins. The bridge rectifier is faulty if the readings are the same for any of the individual diodes.

    Zener Diode

  1. 1

    Unplug the device containing the zener diode. This ensures the zener diode has no power.

  2. 2

    Set the DMM to the "diode test" setting.

  3. 3

    Test the zener diode. Place the two DMM leads on the two zener diode leads. The DMM will read either "OL" or 0.7 volts DC. Switch the DMM leads. A working zener diode exhibits a second reading opposite of the first reading.

Tips and warnings

  • Some electronic circuits retain lethal voltages even when unplugged.
  • Seek professional assistance if you have any hesitations about working on electronic circuits.

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