Multimeter - integrated circuit detection method
1. offline measurement
Off-line measurement When the integrated circuit is not welded into the circuit, the DC resistance value between its pins is measured and compared with the known normal DC resistance value between the pins of the same type of integrated circuit 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 judge whether the integrated circuit is damaged by measuring whether the voltage value, resistance value and current value of each pin of the integrated circuit are normal on the circuit.
3. Substitution method
The substitution method is to replace the tested integrated circuit with a known intact integrated circuit of the same type and specification, and it can be judged whether the integrated circuit is damaged.
4. total current measurement
This method is a method to judge whether the IC is good or bad by detecting the total current of the incoming line of the IC power supply. Since most of the ic is directly coupled, when the ic is damaged (such as a pn junction breakdown or open circuit), it will cause the subsequent stage to be saturated and cut off, causing the total current to change. Therefore, the method of measuring the total current can judge whether the IC is good or bad. It can also be used to measure the voltage drop of the resistor in the power path, and use Ohm's law to calculate the total current value.
We know that when the integrated block is used, there is always a pin that is soldered to the "ground" line on the printed circuit board, which is called the ground pin in the circuit. Since the integrated circuit uses direct coupling, there is a certain DC resistance between the other pins of the integrated block and the ground pin. This certain DC resistance is called the internal equivalent DC resistance of the pin, referred to as R. When we get a new integrated block, we can judge its quality by measuring the internal equivalent DC resistance of each pin with a multimeter. If the internal equivalent resistance R of each pin is in line with the standard value, it means that this block The integrated block is good, otherwise, if the difference from the standard value is too large, it means that the integrated block is damaged inside.
One point must be paid attention to when measuring. Since there are a large number of non-linear components such as triodes and diodes inside the integrated block, it is not possible to judge whether it is good or not by only measuring a resistance value during the measurement. Two resistance values. Only when the positive and negative resistance values in R meet the standard, can it be concluded that the integrated block is intact.
According to the actual maintenance experience, when detecting the DC equivalent resistance inside the integrated circuit, it is not necessary to solder the integrated block from the circuit. It is only necessary to disconnect the pin with abnormal voltage or on-line resistance from the circuit, and at the same time connect the grounding pin to the circuit. The board is disconnected, and the other pins remain in their original state. The positive and negative resistance values in R between the test pin and the ground pin can be measured to judge whether it is good or bad.
