Knowledge of testing and repair of high-frequency diode chips
It is normal for a diode to fail, but if the diode fails, but we don't notice it, we continue to use the diode, which will affect the safety of the circuit. So, how do we detect diode failures in general?
The effective method for detecting 3 diodes in the circuit is to measure the DC voltage on the diode, as shown in the figure below is the schematic diagram of the wiring during measurement. If the DC voltage is measured, the result is 1About 8V, it means that the 3 diodes are working normally; If the result of measuring DC voltage is 0V, it is irrelevant to measure whether the DC working voltage +V is normal and whether the resistance R1 is open, because the possibility of breakdown of the three diodes at the same time is small; If the measured DC voltage result is greater than 18V, check for an open circuit fault in one of the 3 diodes.
Test methods for diodes.
Detection of low-power transistor diodes.
a.Distinguish between positive and negative electrodes.
a) Observe the symbolic markings on the housing. The housing of the diode is usually marked with the symbol of the diode, with a triangular arrow at one end as the positive pole and the other end as the negative pole.
b) Observe the color spots on the housing. On the housing of the point-contact diode, it is usually marked with a polar color dot (white or red). Generally, the end marked with a color point is the positive electrode. Other diodes are marked with a color ring, and the end of the color ring is a negative pole.
c) Based on a measurement with a smaller resistance, one end of the black pen is the positive pole, and the one end of the red pen is the negative pole.
b.Detection of reverse breakdown voltage. In the case of alternating current, because it is constantly changing, the reverse operating voltage is the peak AC voltage that the diode is subjected to.
Detects bidirectional trigger diodes.
Place the multimeter in the corresponding DC voltage stop. The test voltage is provided by a megohmmeter. During the test, shake the megohmmeter and measure the VBR value in the same way. Later, VBO and VBR are compared, and the smaller the difference between the absolute values of the two, the better the symmetry of the bidirectional trigger diode under test.
Detection of transient voltage suppression diodes (TVS).
a.Use a multimeter to measure the quality of the tube For a single-pole TVS, according to the method of measuring ordinary diodes, its forward and reverse resistance can be measured, the general forward resistance is about 4K, and the reverse resistance is infinity.
For the bidirectional polar type TVS, the resistance value between the two pins should be infinity measured by arbitrarily changing the red and black watch pens, otherwise, the tube is not performing well or has been damaged.
Detection of high-frequency varistor diodes.
The difference between the appearance of positive and negative high-frequency varistor diodes and ordinary diodes is that their color code colors are different, the color code color of ordinary diodes is generally black, while the color code color of high-frequency varistor diodes is light color. Its polarity law is similar to that of ordinary diodes, that is, one end with a green ring is the negative electrode, and the other end without a green ring is a positive electrode.
Detection of varactor diodes.
How to measure the red and black pen of the multimeter, the resistance value between the two pins of the varactor diode should be infinity. If the multimeter pointer swings slightly to the right or the resistance value is zero during the measurement, it means that the measured varactor diode has a leakage fault or has been broken down.
Detection of monochromatic light-emitting diodes.
Attach an energy-saving 1 outside the multimeterFor 5V dry batteries, set the multimeter to R 10 or R 100. This connection method is equivalent to giving the multimeter a series of 15V to increase the detection voltage to 3V (the turn-on voltage of LEDs is 2V). During the test, use the two meter pens of the multimeter to alternate the two pins that are in contact with the light-emitting diode. If the tube performance is good, there must be a time when it can emit light normally, at this time, the black watch pen is connected to the positive electrode, and the red watch pen is connected to the negative electrode.
Detection of infrared light-emitting diodes.
a.Distinguish between the positive and negative electrodes of infrared light-emitting diodes. Infrared light-emitting diodes have two pins, usually the long pin is positive and the short pin is negative. Because the IR light-emitting diode is transparent, the electrodes inside the tube shell are clearly visible, and the wider and larger inner electrodes are the negative electrodes, while the narrower and smaller ones are the positive electrodes.
b.Measure the forward and reverse resistance of the red light-emitting diode first, usually the forward resistance should be about 30k, and the reverse resistance should be more than 500k, so that the tube can be used normally.
Detection of infrared receiving diodes.
a.Identify pin polarity.
a) Visually recognizable. Common infrared receiving diodes have a black appearance. When identifying the pins, face the light-receiving window, from left to right, positive and negative. In addition, there is a small bevel plane at the top of the tube body of the infrared receiving diode, usually with this bevel plane with a pin at one end as the negative pole and the other end as the positive end.
b) First use the multimeter to distinguish the positive and negative electrodes of ordinary diodes for inspection, that is, exchange red and black watch pens twice to measure the resistance value between the two pins of the tube, when normal, the obtained resistance value should be one large and one small. The smaller resistance value prevails, the tube foot connected by the red watch pen is the negative pole, and the pin connected by the black watch pen is the positive pole.
b.Detect how good or bad the performance is. The positive and reverse resistance of the infrared receiving diode can be measured with a multimeter resistance, and the quality of the infrared receiving diode can be preliminarily determined according to the magnitude of the positive and reverse resistance values.
Detection of laser diodes.
a.According to the method of detecting the forward and reverse resistance of ordinary diodes, the pins of the laser diodes can be arranged in order. However, it should be noted that because the forward voltage drop of the laser diode is larger than that of ordinary diodes, the multimeter pointer is slightly deflected to the right when detecting the forward resistance.
With the continuous development of science and technology, high-frequency diode chips are more and more widely used in various electronic devices. However, due to its high operating frequency and complex circuit, the testing and maintenance of high-frequency diode chips has become a technically difficult task. This article will focus on the test and repair knowledge of high-frequency diode chips to help readers better understand and master the technology in this field.
1. Testing of high-frequency diode chips.
1.Preparation before the test.
Before testing a high-frequency diode chip, the following preparations need to be made:
1) Familiar with the operation methods of test equipment, such as oscilloscopes, signal generators, spectrum analyzers, etc.;
2) Understand the basic parameters and performance indicators of high-frequency diode chips, such as working frequency, rated current, reverse breakdown voltage, etc.;
3) Prepare the auxiliary tools and materials required for the test, such as soldering station, solder, wire, etc.
2.Test Methods and Procedures.
The testing of high-frequency diode chips mainly includes the following steps:
1) Appearance inspection: observe whether the appearance of the chip is damaged, cracked and other phenomena, and whether the pins are intact and no broken wires;
2) Parameter measurement: use the corresponding test equipment to measure the parameters of the chip, such as forward voltage, reverse current, junction capacitance, etc.;
3) Functional test: By building the corresponding circuit, the function test of the chip, such as frequency modulation, demodulation, amplification, etc.;
4) Stability test: work for a long time in harsh environments such as high temperature and high humidity to observe the performance stability of the chip.
When conducting the test, there are a few things to keep in mind:
1) Ensure that the grounding of the test equipment is good to avoid the influence of interference signals on the test results;
2) Test in strict accordance with the parameter range of the chip to avoid damage to the chip;
3) Record and analyze the test data in detail for subsequent fault location and performance evaluation.
Second, the maintenance of high-frequency diode chips.
1.Precautions before repair.
Before carrying out the repair of the high-frequency diode chip, the following points need to be noted:
1) Understand the working principle and circuit structure of the chip, and avoid more serious failures caused by blind maintenance;
2) Prepare the tools and materials required for maintenance, such as soldering station, solder, wire, etc.;
3) Keep the chip clean during the maintenance process to avoid the impact of dust, dirt, etc. on the circuit.
2.Common faults and maintenance methods.
The common faults and maintenance methods of high-frequency diode chips are as follows:
1) Pin breakage: If a pin is found to be broken, the dirt and oxide at the fracture need to be cleaned up, and then repaired by wire or welding;
2) Performance degradation: If the performance of the chip is found to be degrading, it may be caused by changes in junction capacitance or damage to the internal circuitry, etc. The chip needs to be parameterized or the internal components need to be replaced;
3) Abnormal work: If the chip is found to be working abnormally, it may be caused by unstable power supply voltage or signal interference. The circuit needs to be checked and adjusted.
The following points need to be paid attention to during the repair process:
1) Ensure that the welding quality is good, and avoid virtual welding, missing welding and other phenomena;
2) Make a detailed record of the maintenance process for subsequent failure analysis and performance evaluation;
3) If it cannot be repaired or has no repair value, the chip should be replaced in time.