GW Instek GDM-398 - Manual (Page 30)

MEASUREMENT OPERATION
28
Warning
To avoid possible damage to the Meter and to the device under test, disconnect
the circuit power and discharge all high-voltage capacitors before testing diodes.
To avoid harm to yourself, do not input voltages greater than DC 60V or AC 30V.
1. Insert the red test lead into the Ω terminal and the black test lead into the COM
terminal.
2. Set the rotary switch to and press BLUE button to select the
measurement mode.
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 measured value shows on the display.
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.