What are the methods of using a multimeter to test the quality of the circuit board?
The multimeter can not only be used to measure the resistance of the object to be measured, but also the AC and DC voltage can also be used to measure the DC voltage. Even some multimeters can measure the main parameters of transistors and the capacitance of capacitors. Fully mastering the use of a multimeter is one of the most basic skills in electronic technology. Common multimeters include analog multimeters and digital multimeters.
The pointer type multi-meter is a multi-function measuring instrument with the head as the core component, and the measured value is read by the pointer of the head. The measured value of the digital multimeter is directly displayed in the digital form by the LCD screen, which is easy to read, and some also have a voice prompt function. A multimeter is a meter that shares a meter head and integrates a voltmeter, an ammeter and an ohmmeter.
The DC current range of the multimeter is a multi-range DC voltmeter. The meter head is connected in parallel with a closed-circuit voltage dividing resistor to expand its voltage range. The DC voltage range of the multimeter is a multi-range DC voltmeter. The voltage range can be expanded by connecting a voltage divider resistor in series with the meter head. Different voltage divider resistors have different corresponding ranges.
1. Offline detection
Measure the positive and negative resistance values between each pin of the IC chip and the ground. Compare this with a good IC chip to find the point of failure.
2. Online detection
The detection method of DC resistance is the same as offline detection. But pay attention: To disconnect the power supply on the circuit board to be tested, the internal voltage of the multimeter should not be greater than 6V. When measuring, pay attention to the external influence.
3. AC working voltage test method
Use a multimeter with a dB range to measure the approximate value of the AC voltage on the IC. If there is no dB range, a 0.1-0.5μF isolation DC capacitor can be connected in series with the positive test lead. This method is suitable for ICs with relatively low operating frequencies. However, it should be noted that these signals will be affected by the natural frequency, and the waveforms will be different, so the measured data are approximate.
4. Total current measurement method
By measuring the total current of the IC power supply, to judge the quality of the IC. Since most of the ICs are DC coupled, when the IC is damaged (such as PN junction breakdown or open circuit), it will cause the latter stage to saturate and cut off, causing the total current to change. So measuring the total current can judge the quality of the IC. The current value can be calculated by measuring the voltage on the loop resistance online.
