How to Test a Diode with a Fluke Multimeter

Custom Search
You are an electrician, a technician or an engineer and the diode in a circuit board gets bad. How do you test this diode to confirm it is bad?
Well if you have a multimeter, it is a very simple exercise. Let’s find out how to do this. The diode test can be carried out in either forward or reverse bias.

Forward Bias Test
Good Diode
To begin the test in forward bias, switch the knob on the multimeter to the “DIODE” selection and test as shown below:
Testing a Diode in Forward Bias

Connect the BLACK test lead from the multimeter to the diode cathode (This is a white or black band on one side of one of the diode terminals). Connect the RED test lead of the multimeter to the anode. 

If the diode is good, the readout should show between 0.400 to 0.600 along with a single audible beep (beeping is a basic attribute of most multimeters). 

Bad Diode:
If a diode is bad, you will hear a continuous beep tone from the multimeter with any of the following observed:
(a)  A readout of 0.00
(b) The readout will indicate any number value other than 0.400 to 0.600
(c) The readout will indicate “OL”

Reverse Bias Test:
Good Diode
To test in reverse bias with the knob still in the diode selection, connect the BLACK test lead of the multimeter to the anode of the diode and the RED test lead to the cathode of the diode as shown below. If the diode is good, the display should show “OL”
Testing a Diode in Reverse Bias

Bad Diode:
If the diode is bad, you will hear a continuous beep tone from the multimeter with any of the following observed:
(a) A readout of 0.00
(b) A readout of any value other than 0.400 to 0.600
This is as simple the diode test with a multimeter can get.