February 13, 2025

How to Test Diode using an Analog Multimeter

There are tiny devices within electronic circuits called diodes. The purpose of a diode is to keep an electric current flowing in a single direction. For this to work, one direction must have low resistance, and the other direction must have high resistance. Each diode is manufactured out of semiconductor materials like selenium or silicon.

If you regularly work with electronic components, then you’ll need to test their diodes once in a while to see if they’re still functioning normally. This requires you to use a special tool called a multimeter. You can choose between an analog multimeter and a digital multimeter to perform this test. The measurements that you’ll receive are either in volts or ohms.

The big difference between an analog multimeter and a digital multimeter has to do with how the measurements are displayed. An analog multimeter is an old-fashioned version that has a needle that moves toward the value of the measurement. A digital multimeter has a display screen where the numbers of the measurement just appear on it.

The Steps of Testing a Diode with an Analog Multimeter

Let’s go over the basic steps involved when using an analog multimeter to test a diode.

1) The first thing you must do is disconnect the power source from the diode. If you were to leave the power source connected, it could be dangerous, and it would give you bad results. So, remove the battery or unplug the device from the electrical outlet. That should be good enough. Also, the capacitors should be discharged to eliminate additional voltage still in the system.

2) Locate the selector switch of the multimeter. You should find it in the center of the device. It is a dial that you can rotate left or right. Adjust the selector switch so that low resistance is activated. This equals 1 kilohm. Low resistance needs to be set because it enables the flow of some electric current. The best part is that the diode won’t get overloaded.

3) Take your red lead and put it on the positive end (anode). Now take the black lead and put it on the negative end (cathode). This creates a forward bias diode. In other words, the diode has an electric current flowing in it. If you have trouble spotting the anode from the cathode, just remember the silver striped end is the cathode side.

4) The multimeter should give you a reading to determine the status of the diode. A forward bias diode will likely give you a reading of between 1 and 100 ohms. A reverse bias diode is an open diode with unlimited resistance. If you have low resistance for the forward bias diode or reverse bias diode, then you probably have a shorted diode. In that case, replace it immediately.

5) Turn the selector switch toward 100 kilohms to make it high resistance. Make it a reverse bias diode by connecting the black lead to the anode, and the red lead to the cathode. No electric current flows during this state, but you need the high resistance in order to make this happen properly.

6)  If the diode is working right, then you should see a reading that shows an infinity symbol or the open-loop acronym “OL.” When you see low resistance indicated in the reading, it means you have a defective diode. Your only option is to replace the diode.

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7) A diode replacement could mean nothing more than replacing the batteries. But if you have experience at soldering electronic components, then solder the ends before connecting it to the electric circuit.

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