50
E. Testing Diodes
Warning!
To avoid harms to you, please do not attempt to input voltages higher than 60V
DC or 30V rms AC.
To avoid damages to the Meter or to the devices under test, disconnect circuit
power and discharge all the high-voltage capacitors before testing diodes.
Use the diode test to check diodes, transistors, and other semiconductor devices. The diode
test sends a current through the semicondutor junction, then measure the voltage drop across the
junction. A good silicon junction drops between 0.5V and 0.8V.
To test the diode out of a circuit, set up the Meter as Figure 3-5 and proceed as follows:
1. Insert the red test lead into the terminal and the black test lead into the
COM
terminal.
2. Set the rotary switch to
; and press
BLUE
button to select
measurement mode.
Figure 3-5. Diode Test
3. For forward voltage drop readings on any semiconductor component, place the red test lead
on the component’s anode and place the black test lead on the component’s cathode. The red test
lead polarity is “+” while the black test lead polarity is “- “.
The measured value shows on the display.
The
BLUE
button cycles among resistance, continuity, and diode.
Note
- In a circuit, a good diode should still produce a forward voltage drop reading of 0.5V to 0.8V;
however, the reverse voltage drop reading can vary depending on the resistance of other pathways
between the probe tips.
- Connect the test leads to the proper terminals as said above to avoid error display.
- The LCD will display
OL
indicating either open circuit or wrong polarity connection.
- The unit of diode is volt (V), displaying the positiveconnection voltage-drop value.
- Open circuit voltage approximate 2.8V.
- When diode testing has been completed, disconnect the connection between the testing leads
and the circuit under test and remove the test leads away from the input terminals.
