Integrated Circuit Testing Experience Introduction

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Integrated Circuit Testing Experience Introduction

Introduction to the experience of integrated circuit testing (I) Commonly used testing methods Commonly used testing methods for integrated circuits include online measurement method, non-online measurement method and substitution method. 1. Non-online measurement When the integrated circuit is not soldered into the circuit, the DC resistance value between its pins is measured and compared with the DC resistance value between the pins of the known normal integrated circuit of the same model to determine whether it is normal. 2. Online measurement The online measurement method uses voltage measurement method, resistance measurement method and current measurement method to measure the voltage value, resistance value and current value of each pin of the integrated circuit on the circuit to determine whether the integrated circuit is damaged. 3. Substitution method The substitution method replaces the tested integrated circuit with a known intact integrated circuit of the same model and specification to determine whether the integrated circuit is damaged. (II) Detection of commonly used integrated circuits 1. Detection of microprocessor integrated circuits The key test pins of microprocessor integrated circuits are VDD power supply terminal, RESET reset terminal, XIN crystal oscillator signal input terminal, XOUT crystal oscillator signal output terminal and other line input and output terminals. Measure the resistance and voltage of these key pins to the ground on the circuit to see if they are the same as the normal values (which can be found in the product circuit diagram or related maintenance information). The RESET reset voltage of different models of microprocessors is also different. Some are low-level resets, that is, they are low at the moment of power on and maintain a high level after reset; some are high-level resets, that is, they are high at the moment of switching and maintain a low level after reset. 2. Detection of switching power supply integrated circuits The key pin voltages of switching power supply integrated circuits are the power supply terminal (VCC), the excitation pulse output terminal, the voltage detection input terminal, and the current detection input terminal. Measure the voltage and resistance values of each pin to the ground. If they are significantly different from the normal values, and the peripheral components are normal, it can be determined that the integrated circuit is damaged. For thick-film integrated circuits with built-in high-power switching tubes, you can also determine whether the switching tube is normal by measuring the forward and reverse resistance values between the C, B, and E poles of the switching tube. 4 Basic maintenance knowledge 3. Detection of audio power amplifier integrated circuits When checking audio power amplifier integrated circuits, the voltage and resistance values of the power supply terminals (positive power supply terminal and negative power supply terminal), audio input terminal, audio output terminal and feedback terminal to ground should be detected first. If the data values of each pin are significantly different from the normal values, and the peripheral components are normal, the integrated circuit is damaged internally. For audio power amplifier integrated circuits that cause silent faults, when the power supply voltage is measured normally, the signal interference method can be used to check. When measuring, the multimeter should be set to R×1, the red test lead should be grounded, and the black test lead should be used to touch the audio input terminal. Under normal circumstances, there should be a strong "click" sound in the speaker. 4. Detection of operational amplifier integrated circuits Use the DC voltage range of the multimeter to measure the voltage value between the output terminal of the operational amplifier and the negative power supply terminal (the voltage value is higher when static). Use handheld metal tweezers to touch the two input terminals of the operational amplifier in turn (add interference signals). If the multimeter needle swings significantly, it means that the operational amplifier is intact; if the multimeter needle does not move, it means that the operational amplifier is damaged. 5. Detection of time-base integrated circuits The time-base integrated circuit contains digital circuits and analog circuits, and it is difficult to directly test its quality with a multimeter. The test circuit shown in Figure 9-13 can be used to detect the quality of the time-base integrated circuit. The test circuit consists of resistors and capacitors, light-emitting diodes LED, 6V DC power supply, power switch S and 8-pin IC socket. After inserting the time-base integrated circuit (such as NE555) into the IC socket, press the power switch S. If the time-base integrated circuit under test is normal, the light-emitting diode LED will flash; if the LED is not lit or is always lit, it means that the performance of the time-base integrated circuit under test is poor. Integrated circuit replacement skills 1. Direct replacement Direct replacement refers to directly replacing the original IC with other ICs without any modification, and the replacement does not affect the main performance and indicators of the machine. The replacement principle is: the replacement IC's function, performance indicators, packaging form, pin usage, pin number and spacing are the same. The same function of the IC not only refers to the same function; it should also be noted that the logic polarity is the same, that is, the output and input level polarity, voltage, and current amplitude must be the same. For example: the ICs in the image, TA7607 and TA7611, the former is a reverse high-amp AGC, and the latter is a forward high-amp AGC, so they cannot be directly replaced. In addition, there are ICs that output AFT voltages of different polarities and synchronous pulses of different polarities that cannot be directly replaced. Even if they are products of the same company or manufacturer, they should be distinguished. Performance indicators refer to the main electrical parameters (or main characteristic curves), maximum power dissipation, maximum operating voltage, frequency range, and various signal input and output impedances of the IC, which should be similar to the original IC. Substitutes with low power should have larger heat sinks. 1. Replacement of ICs of the same model Replacement of ICs of the same model is generally reliable. When installing integrated circuits, pay attention to the direction not to make a mistake, otherwise the integrated circuit is likely to be burned when powered on. Some single-row in-line power amplifier ICs have the same model, function, and characteristics, but the direction of the pin arrangement sequence is different. For example, the two-channel power amplifier IC LA4507 has "positive" and "negative" pins, and its starting pin marking (color dot or pit) has different directions; there are ICs without suffixes and ICs with suffix "R", such as M5115P and M5115RP 2. Replacement of ICs of different models ⑴ Replacement of ICs with the same model prefix letters and different numbers. This replacement can be directly replaced as long as the pin functions are exactly the same, and their internal circuits and electrical parameters are slightly different. For example: the accompaniment IC LA1363 and LA1365, the latter has a voltage regulator diode added to the IC's ⑤ pin compared to the former, and the rest is exactly the same. ⑵ Replacement of ICs with different model prefix letters and the same numbers. In general, the prefix letter indicates the manufacturer and the category of the circuit. The numbers after the prefix letter are the same, and most of them can be directly replaced. But there are a few, although the numbers are the same, the functions are completely different. For example, HA1364 is a sound IC, while uPC1364 is a color decoding IC; 4558, the 8-pin is the operational amplifier NJM4558, and the 14-pin is the CD4558 digital circuit; so the two cannot be replaced at all. ⑶ Replacement of ICs with different prefix letters and numbers. Some manufacturers introduce unpackaged IC chips and then process them into products named after the factory. There are also products that are improved to improve certain parameter indicators. These products are often named with different models or distinguished by model suffixes. For example, AN380 and uPC1380 can be directly replaced; AN5620, TEA5620, DG5620, etc. can be directly replaced. 2. Indirect replacement Indirect replacement refers to the method of slightly modifying the peripheral circuit of an IC that cannot be directly replaced, changing the original pin arrangement or adding or removing individual components, etc., to make it a replaceable IC. Principle of replacement: The IC used for replacement may have different pin functions and appearances from the original IC, but the functions must be the same and the characteristics must be similar; the performance of the original machine should not be affected after replacement. ⑶ The power supply voltage must match the replaced IC. If the power supply voltage in the original circuit is high, try to reduce the voltage; if the voltage is low, it depends on whether the replaced IC can work. ⑷ After replacement, measure the static operating current of the IC. If the current is much larger than the normal value, it means that the circuit may self-excite. At this time, decoupling and adjustment are required. If the gain is different from the original, adjust the feedback resistor value; ⑸ The input and output impedance of the replaced IC must match the original circuit; check its driving capability. ⑹ When making changes, make full use of the pin holes and leads on the original circuit board. The external leads must be neat and avoid crossing back and forth, so as to check and prevent circuit self-excitation, especially high-frequency self-excitation; (7) Before powering on, it is best to connect a DC ammeter in series in the power supply Vcc loop, and observe whether the change of the total current of the integrated circuit is normal by decreasing the resistance of the voltage drop resistor from large to small.