Digital multimeter to judge whether the diode is good or bad
Step 1: Check whether the two test leads are inserted correctly.
The red test lead should be inserted into the "Ω/V" jack; the black test lead should be inserted into the common terminal "COM" jack. After confirming that the test leads are plugged in correctly, you can proceed to the next step.
The second step: the selection of range block.
Turn the gear switch to "diode with buzzer gear"; press the power switch "POWER" of the digital multimeter, and when the initial symbol "1" is displayed on the LCD screen, you can proceed to the next step.
The third step: the test operation of the diode.
For diodes with obvious polarity marks, first do a forward test: touch the positive test lead (red) to its positive pole; the negative test lead (black) to its negative pole. Since the digital multimeter is in the test state of the diode block, there is a DC voltage of about 2.6V between the two test leads, the red test lead is a positive voltage; the black test lead is a negative voltage, so at this time, the diode is conducting forward, and the reading displayed on the LCD screen It is its forward resistance value, which should be around 500Ω～700Ω normally. Then exchange the two test leads for the reverse test. Since the diode is reversely cut off at this time, the initial symbol "1" is displayed on the LCD screen, indicating that its reverse resistance value is "m" (infinity). If the above test results are met, it means that the diode under test is good; if the test leads are repeatedly exchanged for forward and reverse tests, the readings are all 0 or close to 0, and the buzzer sounds and the indicator light is on, it means that the diode under test has been short-circuited; If the readings of the forward and reverse tests are both "1", it means that the tested diode has been disconnected; if other readings other than "1" are displayed on the LCD screen during the reverse test, it means that the tested diode has reverse leakage. In the three cases of short circuit, open circuit and leakage in the above test results, the tested diode is judged as damaged and cannot be used in the circuit.
For diodes whose polarity marks are unknown and its positive and negative polarity cannot be judged, test leads can be repeatedly exchanged. If the tested diode is good, there will always be normal forward and reverse resistance readings displayed on the LCD screen during the test. Therefore, when the positive resistance reading of about 500Ω～700Ω is displayed, the red test lead is connected to the positive pole of the diode; the black test lead is connected to its negative pole. In the same way, when the reverse resistance value reading "1" displayed as infinite, the red test lead is connected to its negative pole; the black test lead is connected to its positive pole. In this way, the positive and negative polarity of the diode with unknown polarity marks can be judged exactly; its good or bad judgment has been confirmed in the process of repeatedly exchanging test leads, and the normal, short circuit, open circuit or leakage are still as mentioned above.
