What are Electronic Components?

Electronic components are fundamental building blocks of electronic devices and small machinery, as well as measuring instruments. They are often composed of several parts and are designed to be interchangeable among similar products. These components typically refer to specific parts used in industries such as electrical equipment, radio communications, and instrumentation, encompassing a variety of devices such as capacitors, transistors, filaments, springs, etc., commonly represented by items like diodes.

The array of electronic components includes resistors, capacitors, inductors, potentiometers, vacuum tubes, heat sinks, electromechanical elements, connectors, discrete semiconductor devices, electroacoustic devices, laser devices, electronic display devices, photoelectric devices, sensors, power supplies, switches, micro-special motors, electronic transformers, relays, printed circuit boards (PCBs), integrated circuits (ICs), various circuits, piezoelectric materials, crystal materials, quartz materials, ceramic magnetic materials, substrate materials for printed circuits, specialized electronic functional materials, electronic adhesives (tapes), electronic chemical materials, and related parts and accessories.

To ensure the quality of electronic components, there are international certifications such as the European Union's CE marking, the United States' UL certification, Germany's VDE and TUV certifications, and China's CQC certification, among others. These certifications, both international and domestic, serve to guarantee that the components meet quality standards.

Development history:

The history of electronic components is essentially a condensed version of the history of electronics development. Electronic technology emerged as a new field towards the end of the 19th century and the beginning of the 20th century, experiencing its most rapid growth and widespread application in the 20th century, becoming a significant symbol of modern scientific and technological advancement.

In 1906, American inventor Lee De Forest introduced the vacuum triode, also known as the electron tube, which became the core of the first generation of electronic products. By the late 1940s, the world saw the birth of the first semiconductor triode, which quickly gained global adoption due to its compact size, portability, energy efficiency, and longevity, largely replacing the electron tube. Towards the end of the 1950s, the first integrated circuit appeared, integrating many transistors and other electronic components onto a single silicon chip, pushing electronic products towards miniaturization. Integrated circuits rapidly evolved from small-scale integration to large-scale and very-large-scale integration, driving electronic products towards higher efficiency, lower energy consumption, greater precision, enhanced stability, and intelligence. The development stages of electronic computers perfectly illustrate the characteristics of the four stages of electronic technology development; therefore, the following discussion will use the evolution of electronic computing as a framework to describe these four stages of electronic technology.

The electronic component industry, which emerged and developed rapidly in the 20th century, has revolutionized the world and changed the way people work and live. The history of electronic components is, in fact, the history of the electronics industry.

In 1906, American Lee De Forest invented the vacuum triode to amplify the electrical currents in telephones. Subsequently, there was a strong anticipation for the emergence of a solid-state device that could serve as a lightweight, inexpensive, and long-lasting amplifier and electronic switch. The birth of the point-contact germanium transistor in 1947 marked a new chapter in the history of electronic devices. However, this type of point-contact transistor had a critical weakness in its unstable contact points. While the point-contact transistor was being developed, the concept of the junction transistor was proposed, but it wasn't until the ability to create ultra-pure single crystals and control the conductivity type of crystals that junction transistors truly materialized. In 1950, the earliest practical germanium alloy transistor was created. In 1954, the junction silicon transistor was introduced. Following this, the concept of the field-effect transistor was proposed. With the advent and development of materials technologies such as defect-free crystallization and defect control, crystal epitaxial growth techniques, diffusion doping, high-voltage oxide film fabrication, etching, and photolithography, a variety of high-performance electronic devices emerged. Electronic components gradually transitioned from the vacuum tube era to the transistor era and then to the era of large-scale and very-large-scale integrated circuits, eventually forming the semiconductor industry, a representative of high-tech industries.

Due to the demands of social development, electronic devices have become increasingly complex, necessitating reliability, high speed, low power consumption, lightweight, miniaturization, and low cost. After the concept of integrated circuits was proposed in the 1950s, comprehensive technological advancements in materials, devices, and circuit design led to the successful development of the first-generation integrated circuits in the 1960s. The advent of integrated circuits has epoch-making significance in the history of semiconductor development: it spurred progress in copper core technology and computing, leading to historic transformations in various fields of scientific research and the structure of industrial society. The invention of integrated circuits, based on superior scientific and technological achievements, provided researchers with more advanced tools, which in turn led to the creation of many more sophisticated technologies. These advanced technologies further facilitated the emergence of higher-performance, more cost-effective integrated circuits. For electronic devices, smaller size and higher integration mean shorter response times and faster processing speeds; higher transmission frequencies allow for greater amounts of information to be transferred. The semiconductor industry and semiconductor technology are known as the foundations of modern industry and have also developed into a relatively independent high-tech industry.

Classification:

A.     Basic Components: These products are referred to as components because their manufacturing process does not alter the molecular composition of the original materials. Components operate without the need for external energy and include resistors, capacitors, and inductors, collectively known as Passive Components.

Basic components can be further divided into:

Circuit elements: such as diodes and resistors.

Connection elements: including connectors, sockets, cables, and printed circuit boards (PCBs).

B.     Complex Devices: Products that have altered material molecular structures during manufacturing are called devices.

Complex devices can be categorized into:

Active devices: characterized by their own consumption of electrical energy and the requirement for an external power source.

Discrete devices: including bipolar junction transistors, field-effect transistors, thyristors, and semiconductor resistors and capacitors.

Resistors

In circuit diagrams, resistors are usually denoted by "R" followed by a number, for example, R1 represents resistor number 1. The main functions of resistors in circuits are shunting, current limiting, voltage dividing, and biasing.

Capacitors

Capacitors are generally represented in circuits with "C" followed by a number, for example, C13 represents capacitor number 13. A capacitor consists of two metal films closely spaced apart with an insulating material in between. Its main characteristic is blocking direct current while allowing alternating current to pass through. The capacitance value indicates the capacity to store electrical energy, and the opposition it presents to AC signals is known as capacitive reactance, which depends on the signal frequency and the capacitance value.

Inductors

Although not as commonly used in electronic fabrication, inductors play an equally important role in circuits. Considered as energy storage components similar to capacitors, inductors convert electrical energy into magnetic field energy and store it within the magnetic field. Inductors are denoted by "L" and measured in henrys (H), often using millihenrys (mH) as a unit. They often work together with capacitors to form LC filters, LC oscillators, etc. Additionally, inductors' properties are utilized to create chokes, transformers, relays, and more.

Diodes

Crystal diodes in circuits are typically indicated by "D" followed by a number, such as D5 for diode number 5. Diodes are primarily characterized by their unidirectional conductivity, meaning they conduct well under forward voltage and block or present high resistance under reverse voltage. Due to these characteristics, diodes are widely used in rectification, isolation, voltage stabilization, polarity protection, encoding control, frequency modulation, and noise suppression circuits.

Integrated Circuits

Integrated circuits (ICs) are devices that integrate components such as transistors, resistors, and capacitors onto a silicon wafer using specialized processes, commonly referred to as chips. Analog integrated circuits consist of resistors, capacitors, transistors, etc., and are used to process analog signals, including integrated operational amplifiers, comparators, logarithmic/exponential amplifiers, analog multipliers/dividers, phase-locked loops, power management chips, etc. The main components of analog integrated circuits include amplifiers, filters, feedback circuits, reference source circuits, and switched-capacitor circuits. Their design is typically achieved through manual tuning and simulation by experienced designers. In contrast, digital integrated circuit design is largely automated through the use of hardware description languages and EDA software.

Digital integrated circuits integrate digital logic circuits or systems' components and interconnections onto a single semiconductor chip. Depending on the number of gates or components contained, digital integrated circuits can be classified as small-scale integration (SSI), medium-scale integration (MSI), large-scale integration (LSI), very-large-scale integration (VLSI), and ultra-large-scale integration (ULSI). These circuits include basic logic gates, flip-flops, registers, decoders, drivers, counters, shaping circuits, programmable logic devices, microprocessors, microcontrollers, DSPs, and more.

Products:

Relay

An electronic control component that consists of a control system (input circuit) and a controlled system (output circuit), widely used in automatic control circuits. It functions to control large currents with small currents, acting as an "automatic switch" in automation circuits, playing a key role in regulation, safety protection, circuit conversion, etc.

Types include: automotive relays, signal relays, solid-state relays, intermediate relays, electromagnetic relays, reed relays, wet reed relays, thermal relays, stepping relays, high-power relays, latching relays, polarized relays, temperature relays, vacuum relays, time relays, hybrid electronic relays, delay relays, and other types of relays.

Diode

Known as a semiconductor diode or crystal diode, it is an electronic component that conducts current in one direction, consisting of a PN junction, leads, and packaging.

Types include: switching diodes, general-purpose diodes, zener diodes, Schottky diodes, bidirectional trigger diodes, fast recovery diodes, photodiodes, damping diodes, magneto-sensitive diodes, rectifier diodes, light-emitting diodes, laser diodes, varactor diodes, detector diodes, and other diodes.

Transistor

Generally refers to amplifying devices with three pins, but in English, there are various terms for such devices, and they cannot be generalized. For example, the electronic triode (Triode) is an early type of transistor, which is different from other devices called transistors, and there is no unified term in English to describe all devices with three pins.

Types include: field-effect transistors, magneto-sensitive transistors, switching transistors, thyristors, medium- and high-frequency amplifying transistors, low-noise amplifying transistors, low-frequency, high-frequency, microwave power transistors, photo transistors, microwave transistors, high reverse voltage transistors, Darlington transistors, optocouplers, low-frequency amplifying transistors, power switching transistors, and other transistors.

Capacitor

Also known as a capacitor, represented by C, is a device that stores electrical charge, widely used in DC blocking, coupling, bypass, filtering, tuning circuits, energy conversion, control circuits, etc.

Types include: mica capacitors, aluminum electrolytic capacitors, vacuum capacitors, varnish capacitors, composite dielectric capacitors, glass glaze capacitors, organic film capacitors, conductive plastic potentiometers, infrared thermistors, gas-sensitive resistors, ceramic capacitors, tantalum capacitors, paper capacitors, electronic potentiometers, magnetic sensitive resistors potentiometers, humidity-sensitive resistors, photoresistors potentiometers, fixed resistors, variable resistors, resistor arrays, thermistors, fusible resistors, and other resistors/potentiometers.

Connector

Also known as connectors, plugs, and sockets, they are used to connect two active devices to transmit current or signals.

Types include: terminals, wire harnesses, card slots, IC sockets, fiber optic connectors, terminal blocks, cable connectors, printed board connectors, computer connectors, mobile phone connectors, terminal blocks, wiring bases, and other connectors.

Potentiometer

A variable resistor used for voltage division, which changes the resistance value by moving a metal contact.

Types include: synthetic carbon film potentiometers, slide potentiometers, chip potentiometers, metal film potentiometers, solid potentiometers, single-turn/multi-turn potentiometers, single-gang, dual-gang potentiometers, switch potentiometers, wirewound potentiometers, and other potentiometers.

Protective Components

Used for protection in overload or abnormal conditions.

Types include: temperature switches, thermal fuses, current fuses, fuse holders, self-recovering fuses, and other protective components.

Sensor

A device or apparatus that can convert measured information into a usable signal, including sensitive elements and conversion elements.

Types include: electromagnetic sensors, photoelectric sensors, fiber optic sensors, gas sensors, humidity sensors, displacement sensors, vision/image sensors, and other sensors.

Inductor

A component that produces inductance, usually referred to directly as an inductor.

Types include: ferrite beads, current transformers, voltage transformers, inductor coils, fixed inductors, adjustable inductors, wire-wound inductors, non-wire-wound inductors, choke coils (choke rings, chokes), and other inductors.

Electroacoustic Devices

Devices that convert between electricity and sound, utilizing electromagnetic induction, electrostatic induction, or piezoelectric effect for conversion.

Types include: speakers, microphones, pickups, transmitters, receivers, buzzers, and electroacoustic accessories such as frames, horns, dust caps, diaphragms, T-yokes, magnets, spiders, cones, surrounds, grilles, etc.

Frequency Components

Components used to process signal frequencies.

Types include: dividers, oscillators, filters, resonators, frequency modulators, frequency discriminators, and other frequency components.

Switching Components

Used to control the switching state of circuits.

Types include: thyristors, optocouplers, reed switches, and other switching components.

Optoelectronic and Display

Components used for displaying or sensing light signals.

Types include: display tubes, imaging tubes, indicator tubes, oscilloscope tubes, camera tubes, projection tubes, phototubes, emitters, and other optoelectronic and display devices.

Magnetic Components

Components used for storing magnetic information or sensing magnetic fields.

Types include: magnetic heads, Alnico permanent magnetic components, metal soft magnetic components (powder cores), ferrite soft magnetic components (magnetic cores), ferrite permanent magnetic components, rare earth permanent magnetic components, and other magnetic components.

Integrated Circuits

Circuits with various functions integrated into a single chip.

Types include: television ICs, audio ICs, power modules, DVD player ICs, video recorder ICs, computer ICs, communication ICs, remote control ICs, camera ICs, alarm ICs, doorbell ICs, flashing light ICs, electric toy ICs, temperature control ICs, music ICs, electronic organ ICs, watch ICs, and other integrated circuits.

Electronic Hardware

Various small metal parts used in electronic devices.

Types include: contacts, contact pieces, probes, cores, and other electronic hardware.

Display Devices

Components used for information display.

Types include: dot matrix, LED digital tubes, backlight devices, LCD screens, polarizers, LED chips, LED displays, LCD display modules, and other display devices.

Materials Specific：

Capacitor Materials used for the plates and conductive components.

Electrode Materials / Optical Materials / Temperature Sensing Materials

Materials suitable for use in electrodes, optics, and temperature measurement applications.

Semiconductor Materials / Shielding Materials

Substances used in the construction of semiconductors and for electromagnetic shielding purposes.

Vacuum Electronic Materials / Copper Clad Laminate Materials

Materials designed for use in vacuum electronics and as substrates with a copper coating for PCBs.

Piezoelectric Crystal Materials / Electrical Ceramic Materials

Substances that exhibit piezoelectric properties and ceramics used for electrical insulation or conduction.

Photoelectronic Functional Materials | Contact Materials for High and Low Voltage Applications

Materials that function in the conversion of light to electronic signals, and contact materials used in various voltage scenarios.

Laser Active Media / Thin Film Materials for Electronic Components

Active media for laser operation and thin films tailored for electronic components.

Electronic Glass / Diamond-Like Carbon Films

Specialized glass for electronic applications and films that mimic the properties of diamond.

Expansion Alloys and Bimetallic Strips / Electrical Heating Materials and Elements

Alloys that expand with temperature changes and materials used in the manufacture of heating elements.

Other Materials Specific to Electronics

Terminology:

1.     COB (Chip On Board)

COB involves the direct attachment of an IC chip directly onto a printed circuit board.

2.     COF (Chip On FPC)

In COF, a chip is affixed onto a flexible printed circuit (FPC).

3.     COG (Chip On Glass)

COG refers to the process of mounting a chip directly onto a glass substrate.

4.     EL (Electro Luminescence)

EL technology utilizes thin polymer layers to produce light for LCD applications through electro luminescence.

5.     FTN (Formutated STN)

FTN involves adding a compensatory optical layer to STN for monochrome display purposes.

6.     LED (Light Emitting Diode)

A semiconductor diode that emits light when conducting current.

7.     PCB (Print Circuit Board)

A board that mechanically supports and electrically connects electronic components using conductive tracks, pads, and other features.

8.     QFP (Quad Flat Package)

QFP is a type of surface-mount integrated circuit package with a flat thermally conductive bottom surface.

9.     QTP (Quad Tape Carrier Package)

QTP is a four-sided TCP used for integrated circuit packaging.

10.  SMT (Surface Mount Technology)

SMT refers to the method of making electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards.

11.  TCP (Tape Carrier Package)

TCP is a type of flexible printed circuit where ICs can be mounted.

12.  STN (Super Twisted Nematic)

STN displays with approximately 180 to 270 degrees of twisted nematic structure.

13.  tf (Fall Time)

The fall time represents the speed of response, specifically the time taken for a signal to transition from high to low.

14.  TN (Twisted Nematic)

TN displays with about 90 degrees of twisted nematic structure.

15.  TNR (TN With Retardation Film)

A type of color display that doesn’t use color filters, but instead adds compensatory optical layers to conventional TN glass.

16.  tr (Rise Time)

The rise time signifies the speed of response, particularly the time taken for a signal to transition from low to high.

17.  Vop (Operating Voltage)

Vop is the driving voltage for LCD operation.

18.  Vth (Threshold Voltage)

Vth is the voltage level at which a device begins to conduct.

Identification

Common identification methods for electronic components

Resistors

Resistors are typically labeled as "R" followed by a number, such as R1, to indicate their position in the circuit. They are commonly used for current limiting, voltage division, and biasing.

1.       Parameter Identification: Resistance is measured in ohms (Ω), with common multiples being kilohms (KΩ) and megohms (MΩ). The three main labeling methods for resistors are direct marking, color coding, and numerical coding.

a. Numerical coding is often used for small-sized circuits, where, for example, 472 represents 47 × 100Ω (i.e., 4.7K); and 104 represents 100K.

b. Color coding is the most frequently used method, with colors representing digits and multipliers.

2.       The relationships between color bands and resistance values are as follows:

Color Significant Figures Multiplier Tolerance (%)

Start counting from the side with the narrowest band

Silver/x0.01 ±10

Gold/x0.1 ±5

Black 0 +0 /

Brown 1 x10 ±1

Red 2 x100 ±2

Orange 3 x1000 /

Yellow 4 x10000 /

Green 5 x100000 ±0.5

Blue 6 x1000000 ±0.2

Purple 7 x10000000 ±0.1

Gray 8 x100000000 /

White 9 x100000000 /

Capacitors

1.     Capacitors are typically labeled as "C" followed by a number, such as C13, to indicate their position in the circuit. They are used for energy storage and filtering in electronic circuits.

2.     Identification Methods: Capacitors are identified using the same methods as resistors, including direct marking, color coding, and numerical coding. Capacitance is measured in farads (F), with common multiples being microfarads (uF), millifarads (mF), nanofarads (nF), and picofarads (pF).

The value of larger capacitors is usually directly marked on the component, while smaller capacitors are indicated using letters or numbers.

Inductors

Inductors are typically labeled as "L" followed by a number, such as L6, to indicate their position in the circuit. They are used for energy storage and as a passive element in electronic circuits.

They follow similar identifying methods as resistors and capacitors, including direct marking and color coding.

Diodes

Diodes are commonly labeled as "D" followed by a number, such as D5, to indicate their position in the circuit. They are used for rectification, switching, and signal modulation in electronic circuits.

There are various types of diodes, each serving specific functions, including light emission, isolation, and voltage regulation.

Voltage Regulator Diodes

Voltage regulator diodes are commonly labeled as "ZD" followed by a number, such as ZD5, to indicate their position in the circuit. They are used to stabilize voltage levels in electronic circuits.

Variable Capacitance Diodes

Variable capacitance diodes are designed based on the principle that the capacitance of a PN junction varies with the applied reverse voltage. They are used in high frequency modulation circuits.

Transistors

Transistors are commonly labeled as "Q" followed by a number, such as Q17, to indicate their position in the circuit. They are used for amplification, switching, and signal processing in electronic circuits.

Field Effect Transistors

Field effect transistors (FETs) are known for their high input impedance and low noise characteristics. They are widely used in various electronic devices and offer advantages over traditional bipolar junction transistors.

1.     Electronic Components: These are finished products that do not alter molecular composition when manufactured in a factory. Examples include resistors, capacitors, and inductors, which are passive components with no control or conversion action on voltage and current. According to classification standards, electronic components can be divided into 11 major categories.

2.     Electronic Devices: These are finished products that alter molecular structure during manufacturing. Examples include transistors, vacuum tubes, and integrated circuits, which are active components with control and conversion actions (amplification, switching, rectification, demodulation, oscillation, and modulation) on voltage and current. According to classification standards, electronic devices can be divided into 12 major categories, which can be summarized as vacuum electronic devices and semiconductor devices. Stabilization values: 3.3V, 3.6V, 3.9V, 4.7V, 5.1V, 5.6V, 6.2V, 15V, 27V, 30V, 75V.

Introduction to Testing Methods

Testing electronic components is a fundamental skill in home appliance maintenance and is also crucial in the maintenance and repair of security systems. Many techniques used in these fields are directly borrowed from or inspired by those used in home appliance maintenance. Determining the accurate and effective parameters of electronic components and judging their normality is not a routine task. Different methods must be employed for different components in order to determine their condition. Especially for beginners, it is essential to have a thorough understanding of the testing methods and experiences for commonly used electronic components. The following provides an introduction to the testing experiences and methods for commonly used electronic components.

Resistors

1.       Testing Fixed Resistors

A. Connect the two test leads (without distinguishing positive or negative) to the two terminals of the resistor to measure the actual resistance value. To improve measurement accuracy, the appropriate range should be selected based on the nominal value of the resistor being measured. Due to the non-linear relationship of the ohmic scale, the midsection of the scale has finer divisions. Therefore, the pointer should be positioned as close to the center of the scale as possible, i.e., within the 20% to 80% range of the full scale, to ensure more accurate measurements. Depending on the tolerance level of the resistor, a reading within ±5%, ±10%, or ±20% of the nominal value is acceptable. If it does not match, exceeding the error range indicates that the resistance value has changed.

B. Note: When testing resistors with values in the tens of kilohms or more, do not touch the test leads and the conductive part of the resistor with your hands. If the resistor being tested is removed from the circuit, at least one terminal should be desoldered to prevent other components in the circuit from affecting the test and causing measurement errors. Although the resistance value of a color-coded resistor can be determined by its color bands, it is still advisable to test its actual resistance value with a multimeter.

2.       Testing Cement Resistors

The testing method and precautions for cement resistors are exactly the same as those for testing ordinary fixed resistors.

3.       Testing Fuse Resistors

In a circuit, when a fuse resistor opens due to overload, a judgment can be made based on experience: if the surface of the fuse resistor is blackened or charred, it can be concluded that it was caused by a current far exceeding its rated value; if there are no traces on the surface but it is open, it indicates that the current passing through it is equal to or slightly greater than its rated fuse value. To determine the condition of a fuse resistor with no traces on its surface, a multimeter set to the R×1 range can be used. To ensure accurate measurement, one end of the fuse resistor should be desoldered from the circuit. If an infinite resistance value is measured, it means the fuse resistor has failed open. If the measured resistance value differs significantly from the nominal value, it indicates that the resistor has drifted and should not be used. In practical repair, a few fuse resistors may also exhibit breakdown and short-circuit phenomena in the circuit, and attention should be paid during testing.

4.       Testing Potentiometers

When checking a potentiometer, first rotate the knob to see if the rotation is smooth, if the switch is flexible, and if there is a crisp sound when the switch is turned on and off. Listen for any "scratching" sound from the internal contact point and resistor body of the potentiometer. When testing with a multimeter, select the appropriate resistance range based on the resistance value being measured, and then perform the test using the following methods:

A.      Use the ohmmeter range to measure the "1" and "2" terminals of the potentiometer. The reading should be the nominal resistance value of the potentiometer. If the multimeter pointer does not move or the resistance value is significantly different, it means the potentiometer is damaged.

B.      Check the contact between the potentiometer's wiper arm and resistor element. Use the ohmmeter range to measure the "1" and "2" (or "2" and "3") terminals of the potentiometer. Rotate the shaft counterclockwise to near the "off" position, at which point a smaller resistance value is better. Then slowly rotate the shaft clockwise, and the resistance value should gradually increase, with the pointer in the meter moving steadily. When the shaft is rotated to the extreme position "3," the resistance value should be close to the nominal value of the potentiometer. If the multimeter pointer jumps during the rotation of the potentiometer shaft, it indicates a poor contact fault of the wiper.

C.      Testing Positive Temperature Coefficient Thermistors (PTC)

When testing, use the R×1 range of the multimeter. The specific steps are as follows:

A.      Room Temperature Testing (room temperature close to 25°C): Connect the two test leads to the two pins of the PTC thermistor to measure its actual resistance value. Compare this value with the nominal resistance value, and if they differ by ±2Ω, it is considered normal. If the actual resistance value differs significantly from the nominal value, it indicates poor performance or damage.

B.      Heating Test: After the normal room temperature test, a heating test can be performed by heating the PTC thermistor with a heat source (e.g., a soldering iron) while monitoring its resistance value. If the resistance value increases with temperature, it indicates that the PTC thermistor is functioning properly. If the resistance value remains unchanged, it indicates deteriorating performance and should not be used. Care should be taken to avoid the heat source coming into direct contact with the PTC thermistor to prevent damage.

5.       Testing Negative Temperature Coefficient Thermistors (NTC)

(1)     Measuring the Nominal Resistance Value Rt: Use the same method as for measuring ordinary fixed resistors, i.e., select the appropriate resistance range based on the nominal resistance value of the NTC thermistor to directly measure the actual value of Rt. However, due to the high sensitivity of NTC thermistors to temperature, the following points should be noted during testing:

a)     Rt is the resistance value obtained by the manufacturer at an ambient temperature of 25°C, so when measuring Rt with a multimeter, it should also be done at a temperature close to 25°C to ensure the credibility of the test.

b)     The measurement power should not exceed the specified value to avoid measurement errors caused by current thermal effects.

c)     Pay attention to the correct operation. During testing, do not hold the NTC thermistor body by hand to prevent the influence of body temperature on the test.

(2)     Estimating the Temperature Coefficient αt: Measure the resistance value Rt1 at room temperature, and then use a hot source (e.g., a soldering iron) near the NTC thermistor to measure the resistance value RT2 while simultaneously measuring the average temperature t2 of the NTC thermistor surface with a thermometer.

6.       Testing Varistors

Use the R×1k range of the multimeter to measure the insulation resistance between the two terminals of the varistor in both forward and reverse directions. An infinite resistance value indicates a large leakage current, while a very low resistance value indicates that the varistor is damaged and cannot be used.

7.       Testing Photoresistors

(1)     Cover the light-sensitive window of the photoresistor with a black paper. The pointer of the multimeter should remain relatively stationary, and the resistance value should be close to infinity. A larger value indicates better performance. If the value is very small or close to zero, it indicates that the photoresistor is burnt out and cannot be used again.

(2)     Direct a light source at the light-sensitive window of the photoresistor. The pointer of the multimeter should swing significantly, and the resistance value should decrease. A smaller value indicates better performance. If the value is very large or close to infinity, it indicates that the photoresistor is internally open-circuited and cannot be used.

(3)     Direct the light-sensitive window of the photoresistor towards incident light and shake a small piece of black paper on the shading window. The pointer of the multimeter should move left and right along with the shaking of the paper. If the pointer remains in a fixed position and does not move with the shaking of the paper, it indicates that the photoresistor's photosensitive material is damaged.

Capacitors

1.  Testing Fixed Capacitors

(1)     Testing Small Capacitors Below 10pF: Since the capacity of fixed capacitors below 10pF is too small, it is only possible to qualitatively check for leakage, internal shorts, or breakdown by measuring with a multimeter. Using the R×10k range of the multimeter, the resistance value should be infinite when the two test leads are connected to the two pins of the capacitor. If a zero resistance value (pointer movement to the right) is measured, it indicates that the capacitor is leaking or damaged by breakdown.

(2)     Testing Capacitors from 10pF to 0.01μF for Charging Phenomena: The R×1k range of the multimeter can be used. When the β values of both transistors are above 100 and the penetration current is selected using composite transistors such as 3DG6, the red and black test leads of the multimeter should be connected to the emitter e and collector c of the composite transistor. Due to the amplification effect of the composite transistors, the charging and discharging process of the capacitor under test is amplified, making it easier to observe. It should be noted that when performing the test, especially for testing small capacitors, the test leads should be repeatedly switched between points A and B to clearly observe the movement of the multimeter pointer.

(3)     For fixed capacitors above 0.01μF, the multimeter's R×10k range can be directly used to test whether the capacitor has a charging process and whether there is internal short-circuiting or leakage. The magnitude of the pointer's rightward deflection can be used to estimate the capacitance of the capacitor.

2.  Testing Electrolytic Capacitors

(1)     Due to the much larger capacity of electrolytic capacitors compared to ordinary fixed capacitors, the appropriate range should be selected for different capacities. As a general rule, for capacitors with a capacity of 1-47μF, the R×1k range can be used for measurement, and for capacitors with a capacity greater than 47μF, the R×100 range can be used.

(2)     Connect the red test lead of the multimeter to the negative pole and the black test lead to the positive pole. At the moment of contact, the pointer of the multimeter should deflect significantly to the right (the larger the capacity, the greater the deflection), and then gradually return to the left until it stops at a certain position. This resistance value is the forward leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. In practical terms, the leakage resistance of an electrolytic capacitor should generally be several hundred kΩ or higher, otherwise, it will not function properly. During testing, if there is no charging observed in both directions, i.e., the pointer does not move, it means the capacity has disappeared or there is an internal open circuit. If the measured resistance value is small or zero, it indicates a large leakage current or breakdown of the capacitor and it should not be used.

(3)     For electrolytic capacitors with unclear positive and negative markings, the method mentioned above for measuring leakage resistance can be used for identification. First, measure the leakage resistance, remember the value, and then exchange the test leads to measure another resistance value. The larger of the two measured values is the one corresponding to the correct polarity, i.e., the black test lead is connected to the positive pole, and the red test lead is connected to the negative pole.

(4)     Using the resistance range of the multimeter, charging the electrolytic capacitor in both forward and reverse directions can help estimate its capacitance based on the deflection amplitude of the pointer.

3.  Testing Variable Capacitors

(1)     Gently rotate the spindle by hand; it should feel very smooth without any looseness or jamming. Push the spindle in various directions, such as forward, backward, up, down, left, and right; it should not be loose.

(2)     While rotating the spindle with one hand, lightly touch the outer edge of the rotor plates with the other hand; there should be no feeling of looseness. Variable capacitors with poor contact between the spindle and rotor plates should not be used.

(3)     Place the multimeter in the R×10k range, connect one test lead to the rotor plate and the other to the stator plate of the variable capacitor, and rotate the spindle slowly back and forth. The pointer of the multimeter should remain at an infinite resistance value. During the rotation of the spindle, if the pointer occasionally points to zero, it indicates a short circuit between the rotor and stator plates; if at a certain angle, the multimeter reading is not infinite but shows a specific resistance value, it indicates a leakage between the rotor and stator plates.

Inductors and Transformers

1.       Testing Color-Coded Inductors

Set the multimeter to the R×1 range, and connect the red and black test leads to any one of the terminals of the color-coded inductor. The pointer should deflect to the right. Based on the measured resistance value, the following three situations can be distinguished:

A. If the resistance value of the color-coded inductor is zero, it indicates a short-circuit fault inside.

B. The DC resistance value of the color-coded inductor is directly related to the diameter of the enameled wire used for winding and the number of turns. As long as a resistance value can be measured, the color-coded inductor under test can be considered normal.

2.       Testing Intermediate-Frequency Transformers

A. Set the multimeter to the R×1 range and check the continuity of each winding of the intermediate-frequency transformer according to the winding pin arrangement rules to determine its normality.

B. Insulation Performance Test: Set the multimeter to the R×10k range and perform the following tests:

(1) Resistance value between the primary and secondary windings

(2) Resistance value between the primary winding and the casing

(3) Resistance value between the secondary winding and the casing

The test results can be divided into three cases:

(1) Infinite resistance value: Normal

(2) Zero resistance value: Short-circuit fault

(3) Resistance value less than infinity but greater than zero: Leakage fault

3.       Testing Power Transformers

A. Inspect the external appearance of the transformer for any obvious anomalies. Check for broken coil leads, desoldering, scorch marks on insulation materials, loose fastening screws on the iron core, rust on silicon steel sheets, and exposed winding coils.

B. Insulation Resistance Test: Use the multimeter in the R×10k range to measure the resistance values between the iron core and the primary, between the primary and each secondary, between the iron core and each secondary, and between the electrostatic shielding layer and each secondary, with the pointer of the multimeter remaining at an infinite resistance value. If the pointer does not remain at an infinite resistance value, it indicates poor insulation performance of the transformer.

C. Coil Continuity Test: Set the multimeter to the R×1 range. If a certain winding has an infinite resistance value, it means that this winding has a breakage fault.

D. Identification of Primary and Secondary Coils: The primary and secondary leads of a power transformer are usually led out from two different sides, and the primary winding is often marked with "220V," while the secondary winding is marked with the rated voltage, such as 15V, 24V, or 35V. Based on these markings, the coils can be identified.

E. No-Load Current Test:

(a) Direct Measurement Method: Connect the primary winding of the transformer in series with the 220V AC line and measure the no-load current value with the multimeter set to the AC current range of 500mA. The no-load current value should not exceed 10% to 20% of the transformer's full load current. Generally, the normal no-load current of a common electronic device power transformer should be around 100mA. If it exceeds this value significantly, it indicates a short-circuit fault in the transformer.

(b) Indirect Measurement Method: Connect a 10/5W resistor in series with the primary winding of the transformer, and measure the voltage drop U across the resistor using the multimeter set to the AC voltage range. Then calculate the no-load current Iempty using Ohm's law, i.e., Iempty=U/R.

F. No-Load Voltage Test: Connect the primary of the power transformer to the 220V AC mains, and measure the no-load voltage values of each winding using the multimeter. The measured values (U21, U22, U23, U24) should fall within the specified allowable error range, i.e., the high-voltage winding should be ≤±10%, the low-voltage winding should be ≤±5%, and the voltage difference between the two symmetrical windings with a central tap should be ≤±2%.

G. General small power supply transformers are allowed to have a temperature rise of 40°C to 50°C, and if the quality of the insulating materials is good, the allowable temperature rise can be increased.

H. Identifying the Same-Polarity Ends of Various Windings: When using a power transformer, sometimes two or more secondary windings are connected in series to obtain the desired secondary voltage. When using the series connection method, it is essential to correctly connect the same-polarity ends of the windings. Otherwise, the transformer will not function properly.

I. Comprehensive Testing and Identification of Short-Circuit Faults in Power Transformers: The main symptoms of a power transformer with a short-circuit fault are severe heating and abnormal output voltage of the secondary winding. Generally, the more short-circuits within the coil, the higher the short-circuit current, and the more severe the heating. A simple method to detect whether a power transformer has a short-circuit fault is to measure the no-load current (as previously described). For transformers with short-circuit faults, the no-load current value will be significantly larger than 10% of the full load current. When a short-circuit is severe, the transformer will quickly heat up within a few seconds of being powered on without a load, and touching the iron core will give a burning sensation. In this case, there is no need to measure the no-load current to determine if the transformer has a short-circuit point.

Fault characteristics:

Despite the multitude of electronic components within electrical equipment, their failures follow discernible patterns.

1.       Characteristics of Resistor Damage Resistors are the most numerous components in electrical devices but not the ones with the highest failure rate. The most common failure mode for resistors is an open circuit, with an increase in resistance being less common and a decrease in resistance being quite rare. Resistors come in several types, including carbon film, metal film, wirewound, and fusible resistors. The first two types are most widely used, and their failure characteristics include a higher failure rate for both very low resistances (below 100Ω) and very high resistances (above 100kΩ), while mid-range resistances (like several hundred ohms to tens of kilohms) rarely fail. Low-value resistors typically burn and blacken when they fail, making them easy to spot, whereas high-value resistors seldom show any signs of damage. Wirewound resistors are used for limiting large currents and have relatively low resistances. When they burn out, some may blacken or their surfaces may blister or crack, while others show no visible signs. Cement resistors, a type of wirewound resistor, will break when burned out, otherwise showing no visible signs. Fusible resistors might blow a piece off their surface when they fail, but they never char or blacken. By understanding these characteristics, one can prioritize the inspection of resistors to quickly identify the faulty ones.

2.       Characteristics of Electrolytic Capacitor Damage Electrolytic capacitors are used extensively in electrical devices and have a high failure rate. Their failure can manifest in several ways: a. Loss of capacitance or reduction in capacitance. b. Minor or severe leakage. c. A combination of reduced capacitance and leakage. Methods for identifying damaged electrolytic capacitors include:

•      Visual Inspection: Some capacitors may leak fluid upon failure, leaving oily stains on both the surface of the capacitor and the circuit board underneath; such capacitors must not be reused. Others may bulge, indicating damage and the need for replacement. Hence, quality control during the initial selection of capacitors is crucial, with a preference for reputable brands like Yageo.

•      Touch: After powering on, some capacitors with severe leakage may heat up and even become hot to the touch, necessitating their replacement.

•      Internal Inspection: The electrolyte inside an electrolytic capacitor can dry out after prolonged heating, leading to reduced capacitance. Special attention should be paid to capacitors near heat sinks and high-power components; the closer they are, the more likely they are to be damaged.

3.       Semiconductor Device Failure Characteristics Transistors and diodes commonly fail due to PN junction breakdown or open circuits, with shorts being more frequent. Additionally, there are two other failure modes: one is a decline in thermal stability, which manifests as normal operation at startup but soft breakdown after a period of operation; the other is deterioration in PN junction characteristics, which may test normal under a multimeter set to R×1k, but fail to operate correctly in circuit. Lower range settings on the multimeter, like R×10 or R×1, can reveal increased forward resistance compared to normal values. Testing transistors and diodes in-circuit with an analog multimeter set to R×10 or R×1 can accurately identify faulty PN junctions by comparing forward and reverse resistances. If the forward resistance is not excessively high (normal value) and the reverse resistance is sufficiently high (infinite), the PN junction is considered normal; otherwise, it is suspect and should be desoldered for further testing. This method is effective because the peripheral resistances in the circuit, which are typically in the hundreds or thousands of ohms, have minimal impact on the PN junction resistance when measured with a multimeter on a low resistance setting.

4.       Integrated Circuit (IC) Failure Characteristics The internal structure and functionality of integrated circuits (ICs) mean that partial damage can render them non-operational. IC failures come in two forms: complete failure and poor thermal stability. In the case of complete failure, the IC can be removed and each pin's forward and reverse resistance to ground can be compared with a normal IC of the same model to identify any abnormal resistances. For ICs with poor thermal stability, cooling the suspect IC with anhydrous alcohol while the device is operational can delay or prevent the fault from occurring, aiding in diagnosis. Typically, replacing the IC is necessary to resolve the issue.