But, Comrade Chang Tingdao some said that, "my elementary knowledge is not good, do these things also, how service?" Actually, many daily maintenance work certainly do not need the very profound theory to support, so long as has the elementary knowledge then to be competent has -odd. For example, a radio cassette player all does not have the response (with exchange power supply when), (battery) meets with the direct current as soon as tries, normal work. Such as soon as tries, then may know the alternating current supply feed circuit partially has the breakdown. Again used an avonmeter quantity, the transformer to lead the way. Exchanges the new product, the circular telegram testing, all is normal. The such simple service may say is everybody is all good, only is our some schoolmates continuously lazily to does, is not willing to begin. Causes them not to be willing to go to the dry reason is various, very important is, they thought oneself does not understand the theory, the electric circuit broke down not to know how searched. But in fact, as a result of the technical progress, the manufacture level unceasing enhancement, the product quality also unceasingly enhances, the electric appliance has the major failure opportunity already is very small, are massive all is the use not when causes the system failure, contacts not good, the fuse fuse and so on the small problem, some simply does not need to repair, moves several may recover.

Since we knew, the electric appliance has the big breakdown opportunity not to be certainly many, then has the breakdown when the electric appliance we greatly may not need to be startled, so long as observes carefully, performs to analyze, again tests diagnoses, all may fix the breakdown in many situations.

Moreover, because the electric circuit systematic characteristic (namely electric circuit is composed by a each one function module), when some function module appears the breakdown, we only must wholly absorbed study this part then, but does not need after it overall to understand only then repairs it.

But the speech returns to the original topic, took a serviceman, understands theory Yu Fou is very important, we said takes to begin to practice certainly does not represent may completely not want the theory. After all, can be much more effective under the theory instruction practice. Therefore, we also must diligently study the electric circuit theory knowledge, regardless of is from the textbook or the extracurricular book, causes oneself to both to have the theory knowledge with every effort, and has the virtual rating the goal to make great strides forward.

Hoped comrades looked after this article, all can remove the worry, own begin.

In here will be able to introduce the basic service electric appliance method, the overhaul method overhauls one of work basic skills, to will overhaul the survey for the beginner to understand, this chapter will introduce several overhauls methods, if will have obscurely place may temporarily put aside, will manufacture at the following experiment gradually grasps. These methods certainly are not irrevocable, but should aim at the electric appliance the breakdown nimbly to utilize, can receive the good effect.

Commonly used examination method

(1)th, 直观�?/p>

1. principles

直观�?is through person's eye or other sense organs discovered the breakdown, fixes the breakdown one overhaul method.

2. applications

直观�?is one of most basic trouble shooting methods, after the implementation process should persist simple is first complex, first outside the inside principle. When actual operation, how first faces is turns on the cabinet the question, next is to in the electric appliance all kinds of electronic primary device shape, the name, the representative letter, the electric circuit mark and the function which disassembles all can 11 pair of on numbers. Namely can accurately distinguish the electronic primary device. As 直观�?mainly has two aspects the inspection contents: First is to the material object observation; Second is to the picture observation. Former suits to each kind of overhaul situation, latter mainly uses in to have the picture the video equipment, like television and so on.

When 直观�?overhaul, mainly divides into following three steps:

(1) turns on in front of the cabinet inspection: Observes the electric appliance the semblance, looked whether there is bumps into and injures the trace, on the machine pressed key, the receptacle, the electric appliance equipment segment has a Yuan damage and so on.

After (2) turns on the cabinet the inspection: The observation line board and machine in each kind of equipment, looked whether the fuse does blow a fuse; Whether there is does the primary device bump, the broken line; Whether there is does the resistance scorch, changes color; Whether there is does the electrolytic capacitor leak the fluid, the crack 胀and the distortion; On printed wiring board copper foil and spot are whether good, whether there is was repaired and maintained by the other people, the welding trace and so on, when machine in observes, may use the hand to move some primary devices, the spare part, in order to 直观�?full inspection.

After (3) circular telegram inspection: By now the eye had to look whether there is the electric appliance interior does strike a light, to brave the smoke phenomenon; Whether there is does the ear have to listen to the electric appliance interior unusual sound; Nose important news electric appliance interior whether there is coking taste; The hand must trace some pipes, the integrated circuit and so on whether 烫手, if has exceptionally gives off heat the phenomenon, should immediately closing machine.

3. several explanations

(1) 直观�?the characteristic is extremely simple, does not need other instruments, to overhauls the electric appliance the general breakdown and the damage breakdown has the effect very much.

(2) 直观�?the examination comprehensive nature is stronger, it is with overhauls personnel's experience, the theory knowledge and the specialized skill and so on in close integration with, must handle skillfully, needs massively to practice, can skilled grasp.

(3) 直观�?the examination often passes through in the entire repair entire process, with other examination method coordination uses when the effect is better.

(2)th, resistance law

1. principles

The resistance law is surveys the electric appliance using the avonmeter ohm files the integrated circuit, the transistor various feet and various units electric circuit resistance to ground value, as well as various primary devices own resistance value diagnosis one overhaul method.

2. applications

The resistance law overhauls one of breakdown most essential methods. Generally speaking, the resistance law has "the on-line" measure of resistance and "脱焊 the" measure of resistance two methods.

"on-line" measure of resistance, because was measured the primary device meets in the entire electric circuit, therefore the avonmeter obtains the resistance number receives other multiple branches the influence, when analysis test result should give the consideration, avoids error sentences. Normal measured the resistance number can compared to the primary device solid sign sign note resistance number equal or small, is impossible to exist is bigger than the solid sign sign note resistance number, if, then measured primary device existence breakdown.

"脱焊" measure of resistance, because was measured a primary device end or 脱焊 gets down the entire primary device from the printed wiring board, again uses the avonmeter resistance one method, this method operates bothersomely, but surveys the result accurate, is actually reliable.

(1) switch examination

In each kind of electric appliance switch module very are many, surveys their contact resistance and the separation resistance is judges the switch module quality quality is the most commonly used method. The on-line measure of resistance switch contact resistance should be smaller than 0.5 Omega, otherwise is not good for the contact. The separation resistance generally should be bigger than several kiloohms for to be normal.

(2) primary device quality examination

The resistance law may judge the resistance, the electric capacity, the inductance coil, the transistor quality quality.

When resistance law operation, generally is first tests the on-line resistance the resistance number. After obtains various primary devices resistance number, after the avonmeter red, is black 表棒 must exchange time, then tests a time of resistance number. Does this may remove the external circuit network to the measurement result disturbance. Two tests resistance numbers result needs to analyze makes the reference to use. May 脱焊 further examine to the key suspicion primary device.

(3) meets the plug-in unit to pass breaks the examination

The electric appliance interior meets the plug-in unit to be very many, for example: The earphone jack, the power source transform the plug, on the line board all kinds of meets inserts the module and so on, may use the resistance law to test its quality. For example: With has allocated to 圆孔�?the plug passable plug insertion examines the contact resistance. Meets to other inserts when the module examines, passable has swung meets the plug-in unit to measure its contact resistance, if the resistance number size does not decide, explained has the contact not good breakdown.

3. several explanations

(1) the resistance law to overhauls leads the way or short-circuits the sex breakdown to be extremely effective. In the examination, often first uses on-line measures the way, after found the problem, after may dismantle the primary device examines again.

(2) the on-line test certainly must carry on in the power failure situation, otherwise obtains result plate out of true, but also can damage, damage the avonmeter.

When (3) in examines the integrated circuit which some low voltages (for example 5V, 3V) supplies power, do not have to use the avonmeter R×10k the files, in order to avoid damage integrated circuit.

When (4) resistance law on-line test primary device quality quality, the avonmeter reddish black 表棒 must exchange the test, avoids the external circuit as far as possible to the measurement result influence.

(3)th, voltage law

1. principles

The voltage law is carries on the comparison diagnosis through the survey electronic circuit or the primary device working voltage and with the normal value one examination method.

2. applications

The voltage law examination is in all examinations method is most basic, the most commonly used method. Frequently tests the voltage is all levels of supply voltage, transistor each extremely voltage as well as the integrated block various feet voltage and so on. Generally speaking, whether obtains the voltage the result reflects the electric appliance active status normal important basis. A voltage deviation normal value bigger place, often is a spot which the breakdown is at.

The voltage law may divide into the DC voltage examination and the alternating voltage examines two kinds.

(1) alternating voltage examination

In common electric appliance electric circuit, because of city electricity exchange return route less, relatively says the electric circuit not to be complex, when survey is simpler. Generally may use the avonmeter the exchange 500V voltage files to measure the power transformer 初级�? applied the 220V voltage by now, if did not have, the breakdown possibly was the fuse blows a fuse, the power line and the plug had the damage. If the alternating voltage is normal, the observable power transformer secondary end, looked whether has the low pressure, if does not have the low pressure, then possibly is 初级�? by now applied the 220V voltage, if did not have, the breakdown possibly was the fuse blows a fuse, the power line and the plug had the damage. If alternating voltage normal, the observable power transformer secondary end, looked whether has the low pressure, if does not have the low pressure, then possibly is the primary coil leads the way the sex breakdown to be bigger. But secondarily leads the way the sex breakdown to be very small, because the secondary electricity pulls down, the coil burns out the possibility is not big. In the voltage law examination, must foster the one-handed operation custom, measured when high pressure, must pay attention to the personal safety.

(2) DC voltage examination

The direct class voltage examination, first from the levelling circuit, the voltage-stabilizer circuit output input, which part of electric circuits according to the out-port voltage height which obtains further judges or some primary device has the breakdown.

To surveys the amplifier each level of supply voltage, first should the person this level of power circuit primary device begin, to be usual 电压过高 or low had explained the electric circuit has the breakdown.

The DC voltage law also may examine the integrated circuit various feet working voltage. By now had to act according to services the data and the actual value which the material provided compares determines the integrated circuit the quality.

When non- service material, usually accumulates the experience is very important. For example: The radio cassette player presses down when puts the key, when idling d c operation 电压�?increase must outdo several volts. The common electric appliance entire machine d c operation voltage was equal to the merit puts the integrated circuit the working voltage. The electrolysis electric capacity beginnings and ends voltage, the positive electrode is higher than the cathode. These experiences to examines and the judgement brings conveniently.

3. several explanations

(1) the usual examination alternating voltage and the DC voltage may straight take over the use of the avonmeter survey, but must pay attention to the avonmeter the measuring range and the files position choice.

(2) the voltage measurement is the parallel survey, must foster the one-handed operation custom, in the survey process must the energy be centralized, in order to avoid the avonmeter pen short-circuits two spots.

(3) has when the electric appliance are many to 1 grounding, must pay attention looks after the grounding again surveys.

(4)th, electricity 流法

1st, principle

The electricity 流法 is through examines the transistor, the integrated circuit operating current, each partial electric current and the power source load current judges the electric appliance breakdown one overhaul method.

2. applications

When electricity 流法 examination electronic circuit, may rapidly discover the transistor to give off heat the reason which, primary device and so on power transformer gives off heat, also is examines various pipes and the integrated circuit active status commonly used method. When electricity 流法 examination, often needs to interrupt a circuit. Enters the electric circuit the avonmeter string, this step realizes is more troublesome. When meets the electric circuit to burn the fuse or the local circuit has short-circuits, uses the electricity 流法 test result comparison explanation question

The electricity 流法 examination may divide directly measured the mensuration and indirectly measures the mensuration two kinds.

The electricity 流法 indirect survey is in fact with measured the voltage converts the electric current or estimates the electric current with the special method the size. Wants to measure when transistor this level of electric currents, may through survey on its collecting electrode or the emitter electrode in the series resistance pressure drop converts the magnitude of current.

This method advantage is does not need on the printed wiring board to make the survey mouth. Moreover some electric appliances have established the temperature protective resistor on the essential electric circuit. Through surveys in this kind of resistance the loss of voltage, the again application ohm's law, may estimate in various electric circuits the load electric current size. If some group temperature protective resistor burns out, but straight takes over the use of the avonmeter the electric current files to measure the electric current size, diagnosis reason.

3. several explanations

(1) meets the electric appliance to burn when the insurance or the local circuit has short-circuits, uses the electricity 流法 examination effect to be obvious.

(2) the electric current connects the survey, when the voltage is the parallel survey, the actual operation often first uses the voltage law survey, when necessity only then carries on the electricity 流法 examination.

(5)th, substitution testing method

1. principles

The substitution testing method is same, the performance good primary device 'or' circuit with the specification, replaces on the breakdown electric appliance some to suspect the primary device 'or' circuit which but also inconveniences to survey, thus diagnosis one examination method.

2. applications

Substitution testing method when determination breakdown reason the accuracy is 100%, when operates quite troublesome, sometimes very is difficult, has the certain damage to the line board. Therefore the use substitution testing method needs to act according to the electric appliance breakdown special details, as well as the overhaul existing spare parts and the substitution difficulty degree decides. Should pay attention, in the substitution primary device 'or' circuit process, the connection correctly wants to be reliable periphery, do not have to damage other parts, like this can correctly the diagnosis, enhance the overhaul speed, but also avoids artificially creating the breakdown.

In operation, if suspected when two pins the primary devices lead the way, but does not need to dismantle them, but is welds a same specification again on the line board this primary device pin the primary device, after welds the breakdown to vanish, proved the primary device which suspected is leads the way.

When suspected when some capacitor the capacity reduces, also may select the above direct parallel method.

When substitution local circuit, if suspected some level of amplifiers have the breakdown, may this level of amplifiers out-port separation, look in addition a same model or the similar work normal machine, in similar spot separation, in front of good machine cut-off point works normally. Again moves the cut-off point to suspected this and the amplifier input end, performs the above substitution experiment again, if this time breakdown appearance, then the showing suspicion is correct, otherwise may remove the suspicion object. Above this kind of substitution examination especially suits to the double sound track sound difficult breakdown repair, because the double sound track electric appliance is left, the right sound track electric circuit is completely same, this brings conveniently for the overlapping substitution.

3. several explanations

(1) strictly prohibits the big area using the substitution testing method, carelessly substitutes. This not only cannot achieve fixes the electric appliance the goal, even can further expand the breakdown the scope.

(2) substitutes the testing method generally is after other examination method utilization, has when the significant suspicion to some primary device only then uses.

(3) when must replace primary device when machine base, also must prudently use the substitution testing method, if must use time, should fully disassemble, causes the primary device to expose in outside, has the enough big operation space, is advantageous for substitution processing.

(6)th, oscilloscope law

1. principles

The oscilloscope law uses the oscilloscope track observation signal passage various test points, according to profile whether there is, size and whether distorts the diagnosis one overhaul method.

2. applications

The oscilloscope method characteristic lies in direct-viewing, rapid is effective. Some high-quality oscilloscopes also have the survey electron primary device the function, has provided the extremely convenient method for the examination.

(1) A 类晶�?tube amplifier profile test

In order to guarantee A kind of amplifier non- distortion output, its transistor base extremely bias resistance Rb collecting electrode resistance Re must choose appropriately, otherwise the out-port can have the wave distortion. The oscilloscope law may conveniently observe its wave distortion or not.

(2) B source transistor amplifier profile test

B kind of push-pull amplifier bias when 截止�? does not have the signal the quiescent current is very small. But as a result of collecting electrode electric current non-linearity, when signal amplitude through zero and from a tube to another tube in turn, can have the monkey chatter. In order to prevent the collecting electrode electric current completely cuts off, should extremely add the small bias in 推挽 the transistor base. With the aid of to the oscilloscope, may observe the profile to the resistance parameter choice.

3. several explanations

(1) the oscilloscope method characteristic lies in direct-viewing, may directly demonstrate the waveform through the oscilloscope, also may survey the signal the spurt value.

(2) cannot use the oscilloscope to survey the high pressure or the large scale pulse spot, if in television charactron acceleration extremely with 聚集�?poking head in.

(3) when oscilloscope put in circuit, pays attention to its input impedance bypass function. Usually uses the high impedance, small input capacity poking head in.

(4) the oscilloscope outer covering and the ground terminal must good earth.

Logical inference examination method
(1)th, signal injection method

1. principles

The signal injection method is pours into the signal by the level the electric appliance possibly to exist the breakdown in the related electric circuit, then again and so on determines the data or the profile using the oscilloscope and the voltmeter, whether thus judges all levels of electric circuits normal one examination method.

2. applications

The signal injection method commonly used to examines the radio, the tape recorder or the television channel are partial. To sensitivity low, sound distortion and so on more complex breakdown, this method examines is extremely effective.

The signal injection method examination generally divides two kinds: One kind is along to seeks the law. It is adds the electrical signal in the electric circuit input end, then uses the oscilloscope or the voltmeter survey all levels of electric circuits profile voltage again and so on, which spot thus does the diagnosis leave in; Another kind is the reversion inspection method, is meets the oscilloscope and the voltmeter in the output carries, then adds the electrical signal from after to front by the level, thus finds out the question to be at.

In the test needs to emphasize:

(1) the signal appears in any place, breakdown on possibly before this test, after but is not.

(2) the test point more approaches the speaker, requests the signal scope to be also bigger, like this can drive the speaker to the enough volume. Because full use the equipment the performance is very important.

(3) audioamplifier each level increases probably is 20 ~ 30dB, namely 100 ~ 300 times. If some level of requests input signal oversized, then explained this gain too is low, must do further inspects.

(4 after) if the signal adds to on some level, discovered on the oscilloscope the profile has the serious distortion, then explained distorts possibly occurs in this level.

In summary, uses the signal injection method to be allowed the breakdown isolation to some part or some level. Sometimes even can judge is some part. For example: Some matching plug. Judges regarding the breakdown when some part, may further through other examination method inspection, verify, thus discovers the breakdown to be at.

3. several explanations

(1) the signal pours into a difference, uses the spike is different. In frequency conversion level before must use the high frequency signal, to 检���?between should pour into 465 kilohertz signals in the frequency conversion level, in 检���? should pour into the low-frequency signal to the speaker between.

(2) pours into the signal not only must pay attention to its frequency, but also must choose its level. Adds the signal level best with should edit often works the time signal level to be consistent.

(3) because between the test point and the place has the direct current potential difference, therefore the signal generating device out-port must add the straightforward electric capacity.

(4) examines the electric circuit regardless of is the high-frequency amplification electric circuit, or the low-frequency amplification electric circuit, all chooses by the base extremely or the collecting electrode pours into the signal. Overhauled the multistage amplifier, the signal formerly the level by the level to the after level inspection, also was allowed from the after level by the level to the front level inspection.

(2)th, division law

1. principles

The division law is the electric circuit which has the breakdown implicates divides from the total electric circuit, through the examination, definitely a part, denies a part, one reduces the breakdown scope step by step, finally one examination method which comes out the breakdown spot isolation.

2. applications

The division law is and transfers the electric circuit to the electric appliance electric circuit by many modules or many electric circuits board which the plug-in unit combines, applies is more convenient, for example: Some electric appliance direct current fuse blows a fuse, explained load current oversized, simultaneously causes the power source output voltage to drop. Must determine the breakdown reason, might the ampere meter string in the direct current fuse place, then that part of electric circuits and the total electric circuit minute which suspected using the division law cuts open. By now looked at the joint current the change, after if the minute cut open some part of electric circuits the electric current to fall the normal value, explained the breakdown on in the electric circuit which divided.

The division law differently has the half law, the characteristic point division law, the experience according to its division law divides the law and divides the law point by point and so on.

The so-called half law, is refers the entire electric circuit first one divides into two, which half electric circuit determines the breakdown in; Then will have breakdown half electric circuit again one divides into two, like this time and time again will divide into two, will crash until the examination.

The experience divides the principle is according to the people the experience, which level estimates the breakdown in, then this level input, the out-port takes the minute 割点.

Divides the law point by point, is refers according to the signal transmission order, performs from front to after or from after to front by the level to divide. Actually, the signal injection method which introduced in the above already has used the division law.

Using division law examination electric circuit when must be careful, some electric circuits cannot casually separate must give take, otherwise the breakdown has not removed, but also can add the new breakdown.

3. several explanations

(1) divides the law strictly to say is not one independent examination method, but is must with other examination method coordination uses, can enhance the service efficiency, saves the man-hour.

(2) divides the law to have to be careful in the operation, when specially divides the electric circuit, must prevent damages the primary device and the integrated circuit and the printed wiring board.

(3)th, short-circuits the law

1. principles

Short-circuits the law is short-circuits the electric circuit with an electric capacity either a jumper wire some part or some part, causes it temporarily stall, thus diagnosis one examination method.

2. applications

Short-circuits the law mainly to be suitable the noise which produces in the overhaul breakdown electric appliance, 交流�?or other unwanted signals and so on, regarding judges the electric circuit whether has blocks the sex breakdown to be extremely effective.

Using short-circuits in the law examination electric circuit process, regarding low electric potential, but straight takes over the use of the shorting stub directly to short-circuit to the place; Regarding the high electric potential, should use the exchange to short-circuit, namely uses above 20 mu F the electrolysis electric capacity to the place 短接, the guarantee direct high electric potential is invariable; Cannot casually use to the power circuit short-circuits the law.

For example: Some radio noise is big, by now might use a 100 mu F capacitor, from 检���?led the way its input, the out-port short-circuits the earth, like this will chase the level to carry on in the future. When short-circuits some level of input ends, the radio still had the noise, when short-circuited its out-port namely did not have the noise, then this level was the noise source also is the breakdown level. Is worthy of looking at from the above introduction, short-circuits in the law essence is one kind of special division law.

3. several explanations

(1) short-circuits the law to be only suitable for the noise big breakdown, to 交流�?and whistles by the breakdown not to be suitable. As whistles by the breakdown often to occur in the ring circuit scope, any carries on in this ring circuit 短接, will destroy 自激 the scope condition, will cause 啸叫�?to vanish, causes to be unable accurately to make clear the breakdown the concrete spot.

(2) short-circuits the law examination mainly is the amplifying tube base extremely, between the emitter electrode 短接. Cannot use the collecting electrode to short-circuit to the place

(3) regarding 直� the type amplifier, will affect other transistors a by all means in 短接 period of time from 11 p.m. to 1 a.m the operating point, this sometimes will be able to cause sentences by mistake

Subtotal

Each kind of electronic installation always unavoidably crashes, and further because the electric appliance equipment type is many, possibly appears problem also all sorts of strange and unusual. But speaking of examination technology itself, or has very strongly regular. The people so long as have grasped these rules, also gradually in the course of time the day long will accumulate the experience in the practice. Can rapidly judge crashes the reason, accurately effectively fixes the breakdown.

The electronic circuit examination method are very many, this chapter mainly introduced 直观�? the resistance law, the voltage law, the electricity 流法, the substitution testing method, the division law, short-circuit the law, the signal injection method and the oscilloscope law altogether nine kinds. Which one examination method in the actual overhaul uses to be more effective must look the breakdown electric appliance the special details decide.

When overhaul usually first uses 直观�? some models breakdowns, often use 直观�?the examination to be able to be effective at one fell swoop. Regarding a more covert breakdown, may use the signal injection method or the oscilloscope law, signal injection method comparatively suits to the radio volume and the acoustic fidelity aspect breakdown, but the oscilloscope law to distorts or the sensitivity inferior breakdown is more effective.

Avonmeter examination: It including resistance law, voltage law and electricity 流法. These three kinds are overhaul in the method to be most basic, the most important method. Through the avonmeter examination, can provide the breakdown existence for other each overhaul method the accurate basis.

But some breakdowns inconvenience to the test, often uses the substitution testing method, short-circuits the law and the division law. These methods applications, often can compress the breakdown to a smaller scope in, causes the maintenance work the efficiency enhancement.

Here must emphasize is each examination method all may use for to examine and the judgement many kinds of breakdowns; But the identical kind of breakdown may use the many kinds of examinations method to carry on the overhaul. When overhaul electric appliance breakdown should nimbly utilize each examination method which this chapter introduced, can guarantee the examination works twice the result with half the effort.

In brief, the overhaul process is one kind of comprehensive process: It establishes in to the electric circuit structure profound understanding, correctly unmistakably the logical thinking judgement and skilled operates above the skill. Only has earnestly grasps the overhaul the general rule, and unceasingly summarizes the accumulation experience, the beginner is not the difficult academic society to overhaul each kind of commonly used electric appliance equipment.