How to Troubleshoot Diodes

Diodes come in various sizes and shapes.

Diodes in electronic circuits conduct electricity in one direction, but block it in another. Rectifier circuits use diodes to change alternating current (AC) into direct current (DC) by only allowing the alternating current to pass in one direction.



To test a diode, you must remove at least one of its leads, but it's preferable to remove it completely from the circuit. You need enough electronic skill to remove the diode and operate a digital multimeter. For diodes soldered in place, you need to learn to solder before attempting to remove them.

Things You'll Need

• Basic electronic hand tools, depending on how your diode is mounted
• Multimeter, digital or analog

Instructions

1. 

   You can identify the component on the right as a diode by its single stripe.

   Disconnect power from the equipment before attempting to remove the diode.

2. 

   Use a digital multimeter to troubleshoot diodes in the "diode test" position.

   Remove the diode from the circuit, or disconnect one of its leads. Some diodes plug into sockets, some are held in place with nuts or screws, and some have a combination of mounting methods, including solder. Use a screwdriver to remove screws, and pliers or a small wrench to remove nuts. For soldered connections, melt the solder with a soldering iron in order to remove the diode. (You may need to learn to solder before proceeding, to avoid damaging your equipment.)

3. 

   Use an analog meter in the "Ohms" position.

   Set your digital multimeter to the "Diode Test" position, which is part of the "Ohms" section. If you are using an analog multimeter, set it to the "Ohms" position. Touch the leads of the multimeter together to test it. The reading should be .000 ohms.

4. Touch the meter leads across the diode. Note the reading.

5. Reverse the leads of the meter, and read across the diode in the other direction. Note the reading.

6. Compare the two readings. In one direction, the meter should show a reading indicating that the diode conducts in that direction. In the other direction, the meter should not show any reading.

   A reading in both directions indicates a shorted diode. No reading in either direction indicates an open diode. If your diode is shorted or open, you will need to replace it.

Tips & Warnings

• When testing the diode, do not hold the meter lead tips in both hands. Instead, set the diode on a bench, or use alligator clips.

• If your digital multimeter doesn't have a "Diode Test" position, use the "Ohms" position. The ohm symbol looks a little like a horseshoe.

• Some diodes are physically sensitive, so be careful not to break them when removing or installing them.

References

• OhmCheck: How to Test a Rectifier Diode