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Aug 23 2018

How to Accurately Determine Whether an Integrated Circuit in an Electronic Circuit is Working Properly?


It is an important content to correct the integrated circuit in the circuit to repair the appliance equipment, because it is often to replace the new integrated circuit but the fault still exists


Working principles of IC


IC chip


An integrated circuit  (hereinafter referred to as IC ) is an advanced microelectronic device that integrates many microelectronic devices on a chip. Silicon-based materials are commonly used, N-type and P-type semiconductors and P-N junctions are formed by diffusion or permeation techniques on the device. 

An IC is a semiconductor integrated circuit, that is, a semiconductor material is used as a substrate, two or more components which including at least one active components and some or all of the interconnections are integrated in the substrate or on the substrate, to perform as intermediate or final products of electronic functions.


After understanding the working principle of the IC, it is necessary to go through the following steps to accurately determine whether the IC in the electronic circuit is working properly.

First, we must master the purpose of the IC in the circuit and its internal structure principle and main electrical characteristics, etc., and analyze the internal circuit schematic diagram if necessary. In addition to these, if there are DC voltage, waveform, and the forward and reverse resistance values of each pin corresponding to the ground, then it provides more favorable conditions for pre-inspection judgment.

Then judge the part according to the fault phenomenon, and find out the faulty component according to the location. Sometimes a variety of judgment methods are needed to prove whether the device is indeed damaged. 


IC chip



There are two general methods for checking and judging ICs in a circuit:

One is not judging online, that is, judging the IC in the circuit when it is not soldered to the printed circuit board. In this method, it is difficult to determine the quality of the IC in the circuit without special equipment. Generally, the DC resistance method can be used to measure the forward and reverse resistance values of each pin corresponding to the ground, and then compared with an intact integrated circuit. It is also possible to use an alternative method to insert a suspicious IC into the position of the same type of IC of a normal device, to determine its quality. Of course, it is more assured to use the integrated circuit tester to quantitatively check the main parameters if condition allows.

Another way is the online checking and judging, that is, judging the integrated circuit that is connected to the printed circuit board. Online judgment is the most practical method for overhauling integrated circuits in home appliances. The following is a description of several situations:

The method of DC Working Voltage Measurement 

This method is mainly to measure the DC working voltage value of each pin corresponding to the ground, then compares with the nominal value, according to this to judge the quality of the integrated circuit. Using voltage measurement method to judge the quality of an integrated circuit is one of the most commonly used methods in maintenance, but it is necessary to pay attention to distinguishing non-faulty voltage errors. When measuring the DC working voltage of each pin of the integrated circuit, if the voltage of the individual pin is inconsistent with the voltage value indicated in the schematic or maintenance technical data, do not rush to conclude that the integrated circuit is damaged. The following factors should be excluded first.

1. Check that the provided nominal voltage is reliable.

Because the values on some of the instructions and schematics and other data are quite different from the actual voltage, and sometimes even wrong. So, you should find more relevant data for comparison. If necessary, analyze the internal schematic diagram and peripheral circuits and then make theoretical calculations or estimates to prove whether the voltage is wrong or not.

2. Distinguish the nature of the provided nominal voltage and the voltage at which the operating voltage is.

Because the individual pins of the integrated block change significantly with the injection signal, you can change the position of the band or the record switch at this time, and then observe whether the voltage is normal. If the voltage is normal, it means nominal voltage is a certain operating voltage, and working voltage is in terms of a specific condition, that is, different working states have different measured voltages.

3. Pay attention to the change of the pin voltage caused by the variable components of the peripheral circuit.

When the measured voltage does not match the nominal voltage, it may because an individual pin or a peripheral circuit associated with the pin is connected to a variable potentiometer or switch.  These potentiometers and switches are located at different positions, and the pin voltages are significantly different. Therefore, when a voltage difference between a pin occurs, considering the position of the pin or the potentiometer and switch associated with the pin. Pins can be rotated or pulled to see if the pin voltage is near the nominal value.

4. Prevent errors due to measurement.

Errors may occur due to different internal resistance of the multimeter or different DC voltage levels. In general, the DC voltages are tested with test instruments with internal resistance greater than 20KΩ/V. When using the multimeter with internal resistance less than 20KΩ/V, the measured result will be lower than the original marked voltage. In addition, it should also be noted that the voltage measured on different voltage levels will be different, especially when the large-range files is used, the deviation effect is more significant.


multimeter


5. Judging the importance of the pin voltage to the normal operation of the IC.

When the measured voltage of a pin does not match the normal value, in order to judge whether the IC is good or bad, analysis should be on basis of whether the voltage of the pin has an important influence on the normal operation of the IC and the corresponding change of the voltage of other pins.

6. Judging from the IC pin voltage.

If the voltage of each pin of the IC is normal, the IC is generally considered to be normal. If the voltage of the pin of the IC is abnormal, it should start from the maximum deviation from the normal value. And the imported pumps should check whether the external components are faulty. If there is no fault, the IC is likely to be damaged.

7. A special judgment for the dynamic receiving device.

For example, in a TV set, the voltage of each pin of the IC is different when there is no signal. If the pin voltage that should not change is found to vary greatly, and the one should change is always stable, the IC can be determined to be damaged.

      8. Judgment for devices with multiple modes of operation.

       For example, in a video recorder, the voltage of each pin of the IC is different under different working modes. In this case, the judgment of the IC should be more cautious.


The above points are that the IC does not have a fault in the circuit, and the measured result is different from the nominal value for some reason. Therefore, a test condition should be specified when performing integrated block DC voltage or DC resistance test, especially when recording a measured empirical data.Usually, each potentiometer is rotated to the middle position of the machine, and the signal source adopts the standard signal under a certain field strength. Of course, if the position of each function switch can be recorded again, it is more representative. If the above-mentioned factors are excluded and the measured individual pin voltages are still not in the nominal value, the reason should be further analyzed, but there are two possibilities. One is caused by the failure of the integrated circuit itself. The other is caused by the peripheral circuit of the integrated block.Identifying these two sources of faults is also the key to repair IC home appliances.


The Method of AC Voltage Measurement

In order to grasp the changes of the IC AC signal, the AC operating voltage of the IC can be approximated by a multimeter with a dB plughole. When testing, the multimeter is placed in the AC voltage block, and the positive pen is inserted into the dB plughole. For a multimeter without a dB plughole, it is necessary to connect a 0.1 to 0.5 uF DC blocking capacitor in series with the positive pen. This method is applicable to ICs with relatively low operating frequency, such as video amplification stages and field scanning circuits. Since the natural frequencies of these circuits are different and the waveforms are different, the measured data is an approximation or as a presence or absence.

 


  AC voltage measurement principle


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