Cover Image
close this bookRadio and Electronics (DED Philippinen, 66 p.)
View the document(introduction...)
close this folder1. INTRODUCTION
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View the document1.1. A TRIAL TO STATE A DEFINITION OF ELECTRONICS
View the document1.2. A SHORT HISTORY OF ELECTRONICS
View the document1.3. CLASSIFICATION OF ELECTRONIC DEVICES
close this folder2. PRINCIPLES OF RADIO COMMUNICATION UNICATION
View the document2.1. BASICAL IDEAS ABOUT COMMUNICATION
View the document2.2. DEVELOPMENT OF LONG DISTANCE COMMUNICATION
View the document2.3. FIDELITY AND DISTORTION
close this folder3. TRANSDUCERS
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View the document3.1. MICROPHONES
View the document3.2. LOUDSPEAKERS
View the document3.3. THE TELEPHON SYSTEM
View the document3.4. PROBLEM OF FREQUENCY RANGES
View the document3.5. BANDWIDTH
close this folder4. RADIOWAVES
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View the document4.1. ORIGIN OF RADIOWAVES
View the document4.2. PARAMETERS OF ELECTROMAGNETIC WAVES
View the document4.3. PROPAGATION OF RADIOWAVES
View the document4.4. SPECTRUM OF RADIOWAVES AND BANDS OF RADIOWAVES
close this folder5. MODULATION OF RADIOWAVES
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View the document5.1. THE AMPLITUDE MODULATION (AM)
View the document5.2. FREQUENCY MODULATION (FM)
View the document5.3. SIDEBANDS
View the document5.4. TRANSMISSION OF RADIOSIGNALS
close this folder6. RECEPTION OF RADIOSIGNALS (AM - TYPE)
View the document6.1. AERIAL
View the document6.2. THE TUNED CIRCUIT
View the document6.3. INCIDENTAL REMARK ON BLOCK DIAGRAMS
View the document6.4. DETECTOR OR DEMODULATOR
View the document6.5. POWER SUPPLY
View the document6.6. AMPLIFIER
View the document6.7. SUPERHET RECEIVER (the SUPER)
View the document6.8 INCIDENTAL REMARK ON MIXING FREQUENCIES
View the document6.9. CONSTRUCTION OF A SUPERHETRADIO
close this folder7. COMPONENTS OF MODERN RADIO RECEIVERS
View the document7.1.1. HANDLING OF ELECTRONIC COMPONENTS
View the document7.1.2. HANDLING OF PRINTED CIRCUITS
View the document7.1.3. DIFFERENTIATION OF COMPONENTS
close this folder8. PASSIVE COMPONENTS
View the document8.1. RESISTORS ELECTRICAL CHARACTERISTICS
View the document8.2. CAPACITORS
View the document8.3. INDUCTORS
close this folder8.4. COMBINATION OF PASSIVE COMPONENTS
View the document8.4.1. SERIES CONNECTION OF R AND C, OR R AND L
View the document8.4.2. COMBINATION OF L AND C, RESONANT (TUNED) CIRCUITS
close this folder8.4.3. TUNED CIRCUIT CONNECTED TO AN AC-VOLTAGE
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View the document8.4.4.1. QUALITY OF TUNED CIRCUITS
View the document8.4.4.2. BANDWIDTH
close this folder9. ACTIVE COMPONENTS -1- DIODES
View the document9.1. CHARACTERISTICS OF SEMICONDUCTORS
close this folder9.2. THE PN-JUNCTION OR DIODE
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View the document9.2.1. PN-JUNCTION CONNECTED TO VOLTAGE
View the document9.2.2. CHARACTERISTICS OF A PN-JUNCTION OR DIODE
View the document9.2.3. ZENERDIODE
close this folder10. BLOCKS OF RADIOS / -1- / POWER SUPPLIES
View the document10.1. GENERAL CONSIDERATIONS
View the document10.2. TRANSFORMER
View the document10.3. THE RECTIFIERS.
close this folder10.4. SMOOTHING AND FILTER CIRCUITS
View the document10.4.1. THE RESERVOIR CAPACITOR
View the document10.4.2. FILTER CIRCUITS
close this folder10.5. STABILIZATION
close this folder10.5.1. GENERAL REMARKS
View the document10.5.1.1. LOAD VARIATIONS
View the document10.5.1.2. INTERNAL RESISTANCE OF VOLTAGESOURCES
View the document10.5.1.3. PROBLEMS CAUSED BY THE SMOOTHING CIRCUIT
close this folder10.5.5. METHODS OF STABILIZATION
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View the document10.5.5.1. PARALLEL-STABILIZATION
View the document10.5.2.2. SERIES STABILIZATION
close this folder11. ACTIVE COMPONENTS -2- / TRANSISTORS
View the document11.1. CONSTRUCTION OF A TRANSISTOR
close this folder11.2. CHARACTERISTICS OF TRANSISTORS
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close this folder11.2.1 HANDLING OF CHARACTERISTICS OF TRANSISTORS
View the document11.2.1.1. CONSTRUCTION OF THE STATIC-MUTUAL-CHARACTERISTICS
View the document11.2.1.2. CONSTRUCTION OF THE DYNAMIC MUTUAL CHARACTERISTICS
View the document11.2.1.3. CONSTRUCTION OF THE MAXIMUM-POWER-LINE
close this folder12. AMPLIFIERS
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View the document12.1. STRUCTURE OF A CLASS A AMPLIFIER
View the document12.2. FUNCTION OF A SIMPLE CLASS A AMPLIFIER
View the document12.3. ADVANCED CLASS A AMPLIFIER
View the document12.4. STABILIZATION OF THE QUIESCENT VOLTAGE
close this folder13. CLASS B AMPLIFIERS
View the document13.1. LIMITS OF CLASS A AMPLIFIERS
View the document13.2. CLASS B AMPLIFIERS WITH TRANSFORMERS
View the document13.3. CLASS B AMPLIFIERS WITHOUT TRANSFORMERS
View the document13.4. POWER AMPLIFIER WITH COMPLIMENTARY TRANSISTORS.
View the document14. DETECTOR OR DEMODULATOR
View the document15. AGC-AUTOMATIC GAIN CONTROL
View the document16. IF-AMPLIFIERS
View the document17. FEEDBACK
View the document18. OSCILLATORS
View the document19. FREQUENCY CHANGERS MIXERSTAGE
View the document20. DECOUPLING CIRCUITS
View the document21. MATCHING OF AMPLIFIERSTAGES
View the document22. COUPLING OF AMPLIFIERSTAGES
close this folder23. RADIO SERVICING
View the document23.1. IMPORTANCE AND SUBJECT OF FAULT FINDING
View the document23.2. FAULTS AND FAULT FINDING
View the document23.3. FAULT FINDING METHODS
View the document24. THE USE OF THE OSCILLOSCOPE

23.2. FAULTS AND FAULT FINDING

Repair of devices working on high frequencies is one of the most difficult problems which modern technology can force us to solve.

Almost every radioreceiver consists of a big number of components which seem on the first glance all OK.

Each of them could be the cause of the fault. They do not necessarily look different if they are in a condition of proper working or if they are really faulty.

With our normal senses we can recognize only very minor differences if at all. Burnt resistors, open circuits, spilt condensers, burnt coils and so on, are rather rarely to be found.

In most cases we can only observe effects of faults of which the fact that the loudspeaker is totally dead could be simplest one. Since during fault finding we cannot achieve any development by using our senses, measuring instruments must be applied in order to display the electrical condition in and around the components.

Only this enables us to draw conclusions. The stringing up of such conclusions is defining the method which has to observe all conditions which are important for the operation of the whole device.

THEORETICAL KNOWLEDGE IS ESSENTIAL

If fault finding is not to be done at random, theory is a must. Nobody is able to repair a device reasonably if he does not understand the function of each component and each block of components.

At this point we find the big difference between all other kind of electrical equipment and especially high-frequency equipment. Somebody can be a rather good mechanical engineer (or “fundi”) and for example repair a typewriter very well without knowing the laws governing leverage. Without knowing the laws and effects of electricity, of dc-currents, ac-currents, high- and low-frequencies and so on, nobody will be able to repair an electrical device especially not a radio.

If somebody is starting to repair such a device his first thought has to be to follow the idea which has been put into action with that device.

Looking to the big number and the different kinds of components. It is mostly possible to guess at least which kind of receiver is brought to you.

It would be possible to trace all the circuits contained in it, but this would be very tiresome and a very long procedure. It is obviously much better to collect a good number of circuit diagrams and to refer to the fitting one immediatedly.

But even if the fitting circuitdiagram is available it makes no sense if this is only a collection of symbols and values for the repairing person. He must be able to draw conclusions about the function of each component and he must be able to predict the function of each block within the whole arrangement.

Theoretical reflections must accompany the repair from start to the end.

OBSERVATIONS OF THE RADIO OWNER

Not at all each fault in a radio can be observed if you only operate it only for some minutes. And not at all the radio must be totally dead if it is faulty.

Moreover there are a lot of possible defects which can cause a radio not to operate properly but to operate anyhow. Especially in cases of these defects “in between” (totally dead or normal function) the owner and user of the radio can give us some helpful hints for the repair if we ask him in a clever manner.

It is an additional skill of a radio repair professionalist to talk with his costumers in a way which will enable him to get a good clue for his work. But he has to keep in mind: the costumer is a layman whose conclusions are very often wrong. His sorrow that the bill could be too high may lead him to “bend” the truth.

It is the skill of a professionalist to reach as nears possible to the truth. For example to find out if a fault occured all of a sudden or if there were observed some small defects already before. It is also possible to find out if something has been burning at the fault. You should not neglect this simple method of investigation with the costumer. It can help you to save time with some preliminary steps in fault finding and it will help the costumer to develop a trustful relation to the repairing person, a condition will pay off very soon in getting more costumers.

Every radio technician should act somehow like a good medical doctor.

STATISTICS OF FAULTS

As more experienced a radio technician is, as more he tends to do some preliminary checks before he starts the actual systematical fault finding. That is because experience taught him that there are a certain number of faults which appear much more often than others. Moreover there are certain blocks of radios which show-more often faults than others. If one takes this different probability of faults in account he can draw conclusions where the fault might be located most probably. These experiences can of course influence the method of fault finding. For this reason there was undertaken for quite a number of years a research concerning all kinds of radio receivers. After introduction of integrated circuits there was done a second research of the “fault behaviour” of this new type of receivers.

The results of these two researches are displayed in fig. 217.


fig. 217

The overall number of receivers with integrated circuits having been faulty was remarkably less than the number of only transistorized receivers.

It is nor yet clear if this was due to the fact that integrated circuits equipped receivers have been fairly new in service while normal transistor receivers had already a rather long service time.

In both statistics it is obvious that most of the faults occure in the powersupply section of radios.

Mechanically originated faults like they are caused very often in the push-bot-ton-gear for changing bands or stations are also rather often found. While the faults in HF- and IF-blocks are found very seldom.

Interesting is too, that the number of faults in the AF-sections of radios which integrated circuits is remarkably lower than in radios equipped with normal transistorized circuits.

From these statistics you can draw the following CONCLUSION:

IF YOUR HAVE NO IDEA WHERE TO START WITH FAULT FINDING IT IS MOST PROMISING TO START TO CHECK FIRST THE POWER SUPPLY AND THEN THE AF-SECTION.

THE PRE-CHECK

If you have no clue at all where to start which fault finding you should undertake some simple checks first of all. Aim of this PRE-CHECK is to find out simple faults before you start the actually time consuming fault finding procedure:

1. Switch on the radio, turn the volume control to full. Now check if you hear some noise at the instant of switching. If not: CHECK THE POWER-SUPPLY!

2. While you do the first step (described above) it is adviceable to check by touching the power-transistors, or the power amplifier IC if it is getting hot. If this happens SWITCH OFF IMMEDIATEDLY - THERE MUST BE A SHORT CIRCUIT WITHIN THE POWER-AMPLIFIER.

3. Now you should have a close look to the circuit boards. You should look for any components which show destruction (burnt resistors, spilt capacitors, loose wires or interrupted conducting paths on the printed circuit).

4. Now touch the antenna socket with the antenna plug. You should hear some noise - if not - YOU CAN BE SURE, THAT THERE IS NO OR NOT ENOUGH AMPLIFICATION OF THE INPUT SIGNAL. To localize this fault,....

5. ... Switch the receiver to “sound channel” and touch the audio input with your finger.

You should hear some noise now.

if this is the case:

CONCENTRATE ON IF-STAGES AND MIXERSTAGES

if this is not the case:

CONCENTRATE ON THE AF-AMPLIFIERS.

After this PRE CHECK you can start with the systematical fault finding as it will described now.