What are the methods of using a multimeter to test the quality of the circuit board
The multimeter can be used not only to measure the resistance of the measured object, but also to measure the DC voltage. Some multimeters can even measure the main parameters of transistors and the capacitance of capacitors. It is one of the most basic skills of electronic technology to be fully proficient in the use of multimeters. Common multimeters include pointer multimeters and digital multimeters.
The pointer multimeter is a multi-functional measuring instrument with the meter head as the core component, and the measured value is read by the pointer of the meter head. The measured value of the digital multimeter is directly displayed in digital form by the liquid crystal display, which is easy to read, and some also have a voice prompt function. A multimeter is a meter that combines a voltmeter, an ammeter and an ohmmeter in one head.
The DC current file of the multimeter is a multi-range DC voltmeter. The voltage range can be expanded by connecting the closed-circuit voltage dividing resistor in parallel with the meter head. The DC voltage file of the multimeter is a multi-range DC voltmeter. Connecting the voltage dividing resistor in series with the meter head can expand its voltage range. Different voltage dividing resistors have different corresponding measuring ranges.
1. Offline detection
Measure the positive and negative resistance values between each pin of the IC chip and the ground. Compare it with a good IC chip to find the fault point.
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 influence of the periphery.
3. AC working voltage test method
Use a multimeter with a dB file to measure the approximate value of the AC voltage on the IC. If there is no dB file, 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 frequency. However, it should be noted that these signals will be affected by the natural frequency and waveform, so the measured data are approximate values.
4. Total current measurement method
By measuring the total current of the IC power supply, the quality of the IC can be judged. 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 subsequent stage to be saturated and cut off, and the total current will change. Therefore, measuring the total current can judge whether the IC is good or bad. The voltage on the loop resistance is measured online, and the current value can be calculated.
