1. First of all, we should master the use of IC in the circuit, internal structure principle, main electrical characteristics, etc., and analyze the internal electrical schematic diagram when necessary. In addition, if each pin is to ground dc voltage, waveform and positive and negative dc resistance values, it provides more favorable conditions for pre-inspection judgment.
2. Locate the faulty component based on the fault symptom. Sometimes more than one judgment method is needed to prove that the equipment is really broken.
3. There are generally two kinds of IC inspection and judgment methods in the circuit: one is not online judgment, that is, the IC in the circuit is not welded to the printed circuit board judgment. This method is difficult to determine the quality of IC in the circuit without special equipment. In general, the DC resistance method can be used to measure the positive and negative resistance values between the pins of each pin pair and compare them with a sound integrated circuit. A suspect IC may also be inserted into the position of the same type of IC in the normal equipment by the substitution method to determine its quality. Of course, if conditions allow, you can use integrated circuit tester for quantitative inspection of the main parameters, so that the use of more secure.
4. There are online inspection judgment, which is the judgment method of connecting integrated circuit to printed circuit board. Online judgment is the most practical method of maintaining integrated circuits in TELEVISION, audio, and video equipment. The following situation is as follows:
DC working voltage measurement method: mainly measure the DC working voltage value of each pin to the ground, and then compare with the nominal value to judge the quality of the integrated circuit. It is one of the most common methods in maintenance to judge the quality of integrated circuits by voltage measurement, but attention should be paid to distinguishing non-fault voltage errors. When measuring the DC working voltage of each pin of integrated circuit, if the voltage of individual pin is inconsistent with the voltage value marked in the schematic diagram or maintenance technical data, do not rush to determine the integrated circuit damage, the following factors should be excluded before determining.
1) Whether the supplied nominal voltage is reliable, because the standard value of some specifications, schematics and other data is very different from the actual voltage, and sometimes even wrong. At this point, more relevant data should be found for comparison, internal schematics and external circuits should be analyzed if necessary, and then theoretical calculations or estimates should be made to prove whether the voltage is wrong.
2) Distinguish between the nature of the supplied nominal voltage and the voltage at which it operates. Since the individual pins of the integrated block vary significantly with the injection signal, it is possible to change the band or the position of the recorder switch and then observe whether the voltage is normal. If the latter is normal, the nominal voltage is the operating voltage, which refers to the different measured voltage under specific conditions, that is, the test working state is different.
3) Attention should be paid to pin voltage changes caused by variable components of peripheral circuits. When the measured voltage is inconsistent with the nominal voltage, a potentiometer or switch with variable resistance can be connected (such as volume potentiometer, brightness, contrast, video, fast forward, fast rewind, recorder switch, audio amplitude switch, etc.) due to individual pins or peripheral circuits associated with pins. These potentiometers and switch position is different, the pin voltage is obviously different, so when the pin voltage is inconsistent, consider the pin or the position change of the potentiometer and switch related to the pin, rotate or open the beginning, see whether the pin voltage is close to the nominal value.
4) To prevent errors caused by measurement. The multimeter may cause errors due to different internal resistance or DC voltage levels. In general, the standard DC voltage is measured by measuring the internal resistance of the test instrument greater than 20K ω/V. When the internal resistance is less than 20K ω/V multimeter test, the test result will be lower than the original standard voltage. In addition, it should also be noted that the voltage measured in different voltage ranges will be different, especially in large range ranges, where reading deviations have a greater impact.
5) When the measured pin voltage is inconsistent with the normal value, it should be analyzed according to the important influence of pin voltage on the normal operation of IC and the corresponding changes of other pin voltage to judge the quality of IC.
6) If the IC pin voltage is normal, it is generally considered that IC is normal; If the IC part of the pin voltage is abnormal, start from the maximum value of the deviation from the normal value, the import pump should check whether there is a failure of the peripheral components. If there is no fault, the IC is likely to be damaged.
7) For TV and other dynamic receiving devices, when there is no signal, IC pin voltage is different. If it is found that the pin voltage should not change, but varies greatly, depending on the signal size and the different position of the adjustable element, then IC damage can be determined.
8) For a variety of working mode of equipment, such as video recorder, in different working mode, IC pin voltage is also different.