PCB Tech - How to use a multimeter to repair the circuit board?

PCB manufacturer: How to use a multimeter to repair the circuit board?

Multimeters, also known as multimeters, are indispensable measuring instruments in the electronics manufacturing industry. They generally measure voltage, current, and resistance as their main purpose. Among circuit board manufacturers, its existence is crucial. It can be said to be an essential tool for circuit board repairers.

1. Offline detection
Measure the positive and negative resistance between each pin of the IC chip and the ground. Compare this with a good IC chip to find the fault point.

2. Online testing
1) The detection method of DC resistance is the same as offline detection. But pay attention:

(a) Disconnect the power supply on the circuit board to be tested;

(b) The internal voltage of the universal meter shall not be greater than 6V;

(c) When measuring, pay attention to peripheral influences, such as the potentiometer connected to the IC chip.

2) Measuring method of DC working voltage

Measure the DC voltage of each pin of the IC chip and compare it with the normal value. But also pay attention to:

(a) The universal meter should have enough internal resistance, and the digital meter is the first choice;

(b) Turn each potentiometer to the middle position;

(c) The meter pen or probe should take anti-skid measures, and the bicycle valve core can be placed on the pen tip, and the pen tip should be about 5mm;

(d) When the measured value does not match the normal value, the voltage of the pin should be used to analyze whether the normal value of the IC chip has an impact and the corresponding change in the voltage of other pins;

(e) IC chip pin voltage will be affected by peripheral components. When there is leakage, short circuit, open circuit or deterioration in the periphery;

(f) When the pins of the IC chip are abnormal, start with the large deviation. First check the peripheral components, if there is no fault, the IC chip is damaged;

(g) For circuit boards with dynamic signals during operation, the pin voltage of the IC chip with or without signal is different. However, if the change is abnormal, the IC chip may be broken;

(h) For devices with multiple working modes, the voltage of the IC pin is different in different working modes.

3) AC working voltage test method

Use a universal meter with a dB file to measure the approximate value of the AC voltage on the IC. If there is no dB file, you can insert a 0.1-0.5μF isolation DC capacitor into the positive meter pen. This method is suitable for ICs with relatively low operating frequencies. But it should be noted that these signals will be different by natural frequency and different waveforms. So the measured data are approximate values and are for reference only.

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 IC is DC-coupled, when the IC is damaged (such as PN junction breakdown or open circuit), the subsequent stage will be saturated and cut off, and the total current will change. Therefore, measuring the total current can judge the quality of the IC. The voltage on the loop resistance can be measured online to calculate the current value. The above detection methods have their own advantages and disadvantages. These methods are combined in practical applications. Use them well. Can repair all kinds of circuit boards.