A complete circuit board contains a large number of electronic components. Because of many uncertain factors, the damage of components is very common. When the equipment failure is mostly caused by the damage of components, then the detection and maintenance of components is 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 judge the electrode of rectifier bridge pin first. It is impossible to judge by vision alone, and it is not safe enough.
Remove the capacitor, resistor and rectifier bridge with electric iron
When judging the pin electrode of rectifier bridge, we can use a multimeter to assist. 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 ohm, then the pin touched by the black pen is the negative pole. After judging the positive and negative poles of the red and black pen, the rest of the pins are AC input.
Judge the positive and negative pole of nixie tube with Multimeter
LED is mainly designed for displaying numbers, but it is widely used. So, in the process of maintenance, how to judge whether the LED is damaged?
Similarly, the multimeter can still be used for detection, using R × 10K and R × 100k. First, use the red nose to touch the “ground” lead out of the nixie tube. At this time, the black pen will measure the other lead out in turn. If the test results show that all the sections are normal, the nixie tube is in good condition; if one of the sections is not luminous, the nixie tube is 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 potentiometer?
Adjust the resistance gear of the multimeter, and use the “2” end as the moving contact. If the pointer and resistance of the ohm gear do not move, the potentiometer will be damaged. Then measure whether there is any problem in the contact between the movable arm of the potentiometer and the resistor. You can use the “1, 2” or “2, 3” end of the ohm gear of the multimeter to rotate the resistor shaft counterclockwise to the position close to the “off”, that is, the place with the minimum resistance, and then slowly rotate the shaft clockwise to increase the resistance. When the shaft reaches the limit position, the resistance value should be close to the nominal value of the potentiometer.
The important role of crystal oscillator in circuit board
Crystal oscillator, also known as crystal oscillator, is an electronic component made of quartz. Crystal oscillator is also the abbreviation of quartz oscillator, which is used as an important component of clock circuit, as well as the reference frequency provider of computer network card, graphics card, motherboard and other equipment.
When testing the crystal oscillator, first use the multimeter R × 10K to test the resistance of the crystal oscillator. If the test result is infinite, it means that there is no short circuit and leakage phenomenon. After testing that the resistance is normal, insert the test pen into the test socket, and hold any pin with your finger, and the other pin will touch the metal on the top of the test pen. If the test pen lights up (neon bubble), the crystal oscillator will be in good condition. Otherwise, the crystal oscillator is damaged.