1 Detection of low power crystal diodes

A identifies the positive and negative electrodes.

(a) Observe the symbol marks on the outer casing. The diode symbol is usually marked on the outer casing of the diode, with one end with a triangular arrow being the positive pole and the other end being the negative pole.

(b) Observe the color point on the outer casing. On the housing of the point contact diode, it is usually marked with a polar color point (white or red). Generally, the end marked with a color point is the positive electrode. Other diodes are marked with a color ring, and one end of the color ring is a negative electrode.

(c) The first measurement with a small resistance value is the positive one, and the end connected to the black test pen is the negative pole.

B Detects the highest operating frequency fM.

The operating frequency of the crystal diode, in addition to the relevant characteristics table, is often distinguished by the use of an eye to observe the inside of the diode. For example, a point contact diode belongs to a high frequency tube, and a surface contact type diode is mostly a low frequency tube. In addition, it can also be tested with a multimeter R×1k block. Generally, the forward resistance is less than 1k, which is mostly a high frequency tube.

C Detects the highest reverse breakdown voltage VRM.

For AC, because of the constant change, the highest reverse operating voltage is the AC peak voltage that the diode is subjected to. It should be noted that the highest reverse operating voltage is not the breakdown voltage of the diode. In general, the diode's breakdown voltage is much higher (about one time higher) than the highest reverse operating voltage.

2 Inspection of glass-sealed silicon high-speed switching diode

The method of detecting a silicon high-speed switching diode is the same as the method of detecting a normal diode. The difference is that the forward resistance of this tube is large. With R × 1k electrical blocking measurement, the general forward resistance value is 5k ~ 10k, and the reverse resistance value is infinite.

3 detection fast recovery, ultra fast recovery diode

The method of detecting a fast recovery and ultra-fast recovery diode with a multimeter is basically the same as the method of detecting a plastic-sealed rectifier diode. First, use R × 1k block to detect its unidirectional conductivity, generally forward resistance is about 45k, reverse resistance is infinite; then use R × 1 block to retest once, generally forward resistance is a few, reverse resistance still For infinity.

4 Detection of bidirectional trigger diode

Place the multimeter in the R × 1k block and measure the positive and negative resistance values of the bidirectional trigger diode to be infinite. If the meter is used for measurement, the pointer of the multimeter swings to the right, indicating that the tube under test has a leakage fault. Place the multimeter in the appropriate DC voltage range. The test voltage is provided by a megohmmeter. During the test, shake the megohmmeter and the voltage value indicated by the multimeter is the VBO value of the tube to be tested. Then replace the two pins of the tube under test and measure the VBR value in the same way. Finally, comparing VBO with VBR, the smaller the difference between the absolute values of the two, the better the symmetry of the tested bidirectional trigger diode.

5 Transient Voltage Suppression Diode (TVS) Detection

For the unipolar TVS, the positive and negative resistances can be measured according to the method of measuring the ordinary diode. The general forward resistance is about 4k?, and the reverse resistance is infinite.

For the two-way polar TVS, any red and black test leads should measure the resistance between the two pins to be infinite. Otherwise, the performance of the tube is poor or damaged.

6 Detection of high frequency varistor diode

A identifies positive and negative

The difference between the appearance of the high-frequency varistor diode and the ordinary diode is that the color code color is different. The color code color of the common diode is generally black, and the color code color of the high-frequency varistor diode is light color. The polarity is similar to that of a normal diode, that is, one end with a green ring is a negative electrode, and one end without a green ring is a positive electrode.

B Measure the positive and negative resistance to judge whether it is good or bad.

The specific method is the same as the method of measuring the normal and reverse resistance of a common diode. When using a 500-type multimeter R×1k block measurement, the normal high-frequency varistor diode has a forward resistance of 5k to 55k, and the reverse resistance is infinite.

7 varactor diode detection

Place the multimeter in the R×10k block. Regardless of how the red and black test leads are measured, the resistance between the two pins of the varactor should be infinite. If during the measurement, the pointer of the multimeter is slightly swayed to the right or the resistance is zero, it indicates that the varactor diode under test has a leakage fault or has broken through. For the varactor diode capacity to disappear or the internal open circuit fault, it is impossible to detect with a multimeter. If necessary, the replacement method can be used to check and judge.

8 Monochrome LED detection

Attach a 15V dry battery to the outside of the multimeter and set the multimeter to R×10 or R×100. This connection is equivalent to connecting a 15V voltage to the multimeter to increase the detection voltage to 3V (the LED's turn-on voltage is 2V). During the test, use the multimeter and the two pens to alternately contact the two pins of the LED. If the performance of the pipe is good, it must be able to emit light normally. At this time, the black test pen is connected to the positive electrode, and the red test pen is connected to the negative electrode.