Tips for judging the quality of electronic components using a multimeter
A complete circuit board contains a large number of electronic components. Due to many uncertain factors, component damage is very common. When equipment malfunctions are mostly caused by damage to components, the detection and maintenance of components becomes very important. How to judge the quality of a component is a skill that an engineer must learn.
When repairing, it is often necessary to first determine the electrodes of the rectifier bridge pins. It is impossible to judge by sight alone, and it is not safe enough.
Measurement of nominal resistance of potentiometer
When judging the rectifier bridge pin electrode, we can use a multimeter to help. In the R×1K gear state, use the black pen of the multimeter to touch any pin of the bridge stack, and the red pen to test the other pins. At this time, if the multimeter displays infinity, you can determine that the pin touched by the black pen is the positive output 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 the negative pole. After the positive and negative polarity are determined, the remaining pins are AC inputs.
Use a multimeter to determine the positive and negative poles of the digital tube
Luminescent digital tubes are mainly designed to display numbers, but they are widely used. So, during the maintenance process, how to judge whether the LED digital tube is damaged?
Similarly, you can still use a multimeter to test here, using the R×10K scale and R×100K scale. First use the red nose to touch the "ground" terminal of the digital tube. At this time, use the black pen to measure the other terminals in turn. If the test result is that all segments light up normally, the digital tube is intact; if one section does not light up, the digital tube Damaged.
When judging a potentiometer, you should first measure the nominal resistance of the potentiometer. How to measure the nominal resistance of a potentiometer?
Adjust the resistance range of the multimeter and use the "2" end as the moving contact. If the pointer does not move and the resistance does not move in the ohm range, the potentiometer is damaged. Then measure whether there is any problem with the contact between the movable arm of the potentiometer and the resistor. You can use the "1, 2" or "2, 3" ends of the ohm scale of the multimeter to rotate the resistor shaft counterclockwise to the "off" position, which is where the resistance is smallest, and then slowly rotate the shaft clockwise. , the resistance gradually increases. When the rotating shaft reaches the extreme position, the resistance value should be close to the nominal value of the potentiometer.
The important role of crystal oscillator in circuit boards
Crystal oscillator, also called crystal oscillator, is an electronic component made of quartz. Crystal oscillator is also the abbreviation of quartz oscillator. It is used as an important component of clock circuits and is also the reference frequency provider for computer network cards, graphics cards, motherboards and other equipment.
When testing the crystal oscillator, first use the multimeter R×10K range to detect the resistance of the crystal oscillator. If the test result is infinite, it means that there is no short circuit or leakage in the crystal oscillator. After checking that the resistance is normal, insert the test pen into the test socket, hold any pin with your fingers, and touch the other pin to the metal on the top of the test pen. If the test pen lights up (neon bubble), the crystal oscillator is intact. . Otherwise, the crystal oscillator is damaged.
