Multimeter to judge the quality of electronic components
A complete circuit board contains a large number of electronic components, and it is very common for components to be damaged due to many uncertain factors. When the failure of equipment is mostly caused by the damage of components, the detection and maintenance of components is very important at this time. How to judge the quality of a component is a skill that an engineer must learn.
During maintenance, it is often necessary to judge the electrodes of the rectifier bridge pins first, which cannot be judged by vision alone, and it is not safe enough.
Use a soldering iron to remove the capacitor resistor and rectifier bridge for step-down
When judging the pin electrodes of the rectifier bridge, we can use a multimeter to help. In the R×1K gear state, touch any pin of the bridge stack with the black pen of the multimeter, and test the other pins with the red pen. At this time, if the multimeter shows infinity, it can be judged that the pin touched by the black pen is the output positive pole of the bridge stack. If the display range is 4K-10K ohms, then the pin touched by the black pen is the negative pole, and the pin touched by the red and black pen is negative. After the positive and negative poles are judged, the rest of the pins are AC input.
Use a multimeter to judge the positive and negative poles of the digital tube
Light-emitting digital tubes are mainly designed for displaying numbers, but they are widely used. So, in the maintenance process, how to judge whether the LED digital tube is damaged?
Similarly, a multimeter can still be used for detection here, and the R×10K and R×100K files are used. First use the red nose to touch the "ground" terminal of the nixie tube. At this time, the black pen will measure the other terminals in turn. If the test result shows that all sections are illuminated normally, the nixie tube is intact; if one section does not emit light, the nixie tube Damaged.
Measurement of Nominal Resistance of Potentiometer
When judging the potentiometer, the nominal resistance of the potentiometer should be measured first. How to measure the nominal resistance of the potentiometer?
Adjust the resistance gear of the multimeter, and use the "2" terminal as a moving contact. If the pointer of the ohm gear does not move and the resistance value does not move, the potentiometer is damaged. Then measure whether there is a problem with the contact between the movable arm of the potentiometer and the resistor sheet. You can use the "1, 2" or "2, 3" end of the ohm range of the multimeter to rotate the resistor shaft counterclockwise to the position close to "off", which is the place where the resistance is the smallest, and then slowly rotate the shaft clockwise , the resistance gradually increases. When the shaft reaches the limit position, the resistance value should be close to the nominal value of the potentiometer.
The important role of the crystal oscillator in the circuit board
Crystal oscillators, also known as crystal oscillators, are electronic components made of quartz. Crystal oscillator is also the abbreviation of quartz oscillator, which is used as an important component of the clock circuit, and is also the reference frequency provider of equipment such as computer network cards, graphics cards and motherboards.
When detecting the crystal oscillator, first use the multimeter R×10K to detect the resistance of the crystal oscillator. If the detection result is infinite, it means that the crystal oscillator has no short circuit and leakage. After detecting that the resistance is normal, insert the test lead into the test socket, and pinch any pin with your fingers, and the other pin touches the metal on the top of the test lead. If the test lead lights up (neon bubble), the crystal oscillator is in good condition. . Otherwise, the crystal oscillator is damaged.
