Fault detection techniques for integrated circuit damage

Today's electronic products are often damaged due to an integrated circuit, resulting in one or several parts can not always work, affecting the normal use of equipment. So how to detect the quality of integrated circuits? Usually there are many integrated circuits in a device. When you get a faulty integrated circuit device, you first need to determine the general location of the fault and then pass Measure, gradually reduce the possible parts of the fault, and finally find the fault.

To find the fault must pass the test, usually repair personnel are using the measured pin voltage method to determine, but this can only determine the approximate location of the fault, and some of the pin reaction is not sensitive, and even some no response. In the case of voltage deviation, it also includes the factors of the external component damage, and the internal fault of the integrated block must be strictly distinguished from the external fault. Therefore, a single method is difficult to detect for the integrated circuit and must rely on the synthesis. Testing methods. Take multimeter test as an example to introduce its specific method.

In actual repairs, on-road measurements are usually used. First measure the voltage of its pin. If the voltage is abnormal, disconnect the pin to measure the terminal voltage to determine whether the voltage change is caused by the external component or the internal of the integrated block. It can also be judged by measuring the DC equivalent resistance (called R outside) between the external circuit and the ground. Usually, the DC resistance (in-circuit resistance) between the pin and the grounding pin of the manifold is measured in the circuit. It is the total DC equivalent resistance of R and R in parallel. In the repair, the circuit voltage is often used in conjunction with the on-road resistance measurement method. Sometimes the road voltage and the resistance deviated from the standard value in the road, not necessarily the damage of the integrated block, but the damage on the external components, so that R outside is not normal, resulting in an abnormality in the road voltage and resistance in the road. At this time, only the internal DC equivalent resistance of the manifold can be measured to determine if the manifold is damaged.

We know that when the manifold is used, there is always one pin that is soldered to the “ground” wire on the printed circuit board, which is called the ground pin in the circuit. As direct coupling is used inside the integrated circuit, there is a definite DC resistance between the other pins of the integrated block and the grounding pin. This determined DC resistance is called the internal equivalent DC resistance of the foot, abbreviated as R inside. When we get a new integrated block, we can use the multimeter to measure the internal equivalent DC resistance of each pin to judge whether it is good or bad. If the internal equivalent resistance R of each pin matches the standard value, this indicates that The integrated block is good. On the other hand, if the difference from the standard value is too large, it indicates that the integrated block is internally damaged. One thing must be noted when measuring, because there are a large number of triodes, diodes and other non-linear components inside the integrated block, it is impossible to judge whether it is good or bad when measuring a single resistance in the measurement. It is necessary to exchange the test leads and measure them again to obtain positive and negative results. Two resistances. Only when the positive and negative resistance values ​​in R are in line with the standards can the integrity of the manifold be concluded.

According to the actual maintenance experience, it is not necessary to remove the integrated block from the circuit when detecting the DC equivalent resistance in the integrated circuit. It is only necessary to disconnect the voltage or the pin with the abnormal road resistance from the circuit, and also connect the ground pin to the circuit. The board is disconnected, and the other leg remains as it is. The resistance value between the test pin and the ground pin in R is measured to determine whether it is good or bad.

For example, the TA7609P chip in the TV has an abnormal circuit voltage or resistance and can cut off the pin and pin 5 (ground pin) and then block the resistance between pin 5 and pin 5 with a multimeter and measure a value. Exchange the test leads again. If the integrated block is normal, it should be 8.2kΩ when the red meter is grounded, and 272kΩ when the black meter is grounded. Otherwise, the integrated block is damaged. In the measurement of most of the pins, multimeter with R & TImes; 1k block, when the individual pin R is very large, use R & TImes; 10k block, this is because R & TImes; 1k blocks the battery voltage in its watch only 1.5V, when the integrated block When there are many internal transistors connected in series, the voltage in the meter is too low to allow the transistors in the integrated block to enter the normal operating state, and the value cannot be displayed or inaccurate.

In short, it is necessary to carefully analyze when testing, flexibly apply various methods, explore laws, and quickly and accurately identify faults.