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How to Test Diode Without Multimeter (Step by Step Guide)

A diode is an electronic component with two terminals – cathode and anode terminals. Diodes are an integral part of circuit boards. The purpose of diodes in circuits is to ensure a unidirectional flow of current.

As it is the order with most electronics and electrical components, they sometimes break down or fail, requiring replacement. However, before replacing the electronic components it is essential to test them to find the specific failed component.

Diodes mainly fail when the forward current is excessive or when there is a large reverse voltage.

Sometimes you can spot a bad diode in a printed circuit board without the need of using different test methods. This is if there is black smoke around the outer surface of the diode, meaning the diode has burnt.

If there are no visible black smoke spots, you can use various testing methods to find out if a diode is good or not.

The most common way of testing a diode is by using a multimeter. However, you may not always have a multimeter with you or it may not be working. As such, it is essential you know how to test a diode without a multimeter.

Below are ways to test whether a diode is working or not without a multimeter.

Using a Continuity Circuit

This is a straightforward method of testing a diode without a multimeter. To conduct the test using this method, you only require a few components to design a continuity circuit and some basic electronics concepts. The following are the steps to guide you.

Step 1: Acquire the Requisite Materials

You will need a working LED bulb, bulb holder, battery, the diodes you want to test, two pieces of insulated wires with alligator clips on both ends – insulated black and red.

Step 2: Connect the Components into a Continuity Circuit

To make a continuity circuit first connect the positive terminal of the LED bulb to the positive terminal of the battery using a wire. Then connect the negative terminal of the LED bulb to one of the terminals of the diode.

Using the alligator clip clamp one end of the other piece of wire to the negative terminal of the battery and the other end on the remaining free terminal of the diode.

Step 3: Conduct Forward and Reverse Bias Tests

When the diode is connected on forwarding bias, the circuit will be complete and the led bulb will glow. This is the first test and it shows the diode has passed the test. If the bulb does not glow, it means it is either bad or in reverse bias.

To be sure, interchange the connection on the diode and conduct the second test. If the bulb is lit before the terminal interchange and does not light after the terminals are interchanged, it means the diode is good.

If the bulb does not glow on both occasions, the diode is bad and needs replacement or should not be used on a circuit board.

Using a Component Tester

This is also a simple technique. It involves using a component tester also known as a transistor tester. With just the press of a button, a component tester can indicate the type of electronic component you are testing and the parameters of the component you are testing.

In addition to testing a diode, a component tester can also test transistors, capacitors, inductors, and resistors.

The step-by-step guide of using a component tester to test a diode is as follows;

  1. Turn the component tester on
  2. In the socket area of the tester place the diode you want to test
  3. Press the test button to run a test on the diode
  4. For a good diode, you will see Vf (forward voltage) on the screen
  5. The Vf of a good Si diode is about 0.7 and that of a Ge diode is 0.3


Just like most electronic components, diodes fail. The main contributing factors to the failure of diodes are excessive current flow during forwarding bias and reverse bias.

Sometimes you can spot a bad diode if there is a visible black smoke spot on it. However, if there is no black smoke spot, you need to conduct a test to identify if a diode is good or bad.

If you do not have a multimeter around, you can test a diode using either a continuity circuit or component tester.

When using a continuity circuit, your first step is acquiring the requisite materials, then connecting the components into a continuity circuit, and finally conducting forward bias and reverse bias tests.

A good diode only conducts on the forward bias. If the diode does not conduct current on both forward and reverse bias it is damaged.

The steps for testing diode using a component tester involve;

  • Turning on the component tester
  • Placing the diode under test in the socket area of the tester
  • Pressing the test button
  • For a good diode, you will see Vf (forward voltage) on the screen