How to test a general-purpose diode Those who do not have a multimeter, or other instrument that allows diode tests to be carried out, can easily do this type of test with the circuit shown in the figure. The diode test serves to test diodes of all types, if their working voltage is greater than 3 V and their maximum current greater than 10 mA. Two indicator LEDs are used. The test diode is connected to the terminals shown in the figure. If an LED lights up, it is a sign that the diode is in good condition, and this LED, at the same time, gives the identification of the diode terminals under test. If the two LEDs light up, it is a sign that the test diode is shorted. If none of the LEDs light up, the diode is open. The transformer used has a primary winding according to the local and secondary network from 3 to 6 V, with a current of at least 100 mA. The resistor is 270- or 330-ohms x ¼ W. LEDs are common, and the reader can use both red or one red and one green.
