Test electronic components: Testing a diode with a multimeter

The techniques used for each type of meter are very different so they are treated separately:

Digital multimeters have a special setting for testing a diode, usually labelled with the diode symbol.
Connect the red (+) lead to the anode and the black (-) to the cathode. The diode should conduct and the meter will display a value (usually the voltage across the diode in mV, 1000mV = 1V).
Reverse the connections. The diode should NOT conduct this way so the meter will display "off the scale" (usually blank except for a 1 on the left).

Set the analogue multimeter to a low value resistance range such as × 10.
It is essential to note that the polarity of analogue multimeter leads is reversed on the resistance ranges, so the black lead is positive (+) and the red lead is negative (-)! This is unfortunate, but it is due to the way the meter works.
Connect the black (+) lead to anode and the red (-) to the cathode. The diode should conduct and the meter will display a low resistance (the exact value is not relevant).
Reverse the connections. The diode should NOT conduct this way so the meter will show infinite resistance (on the left of the scale).

For further information please see the diodes page.
You may find it easier to test a diode with the simple tester project.