communication engg lab

8/8/2019 Communication Engg Lab

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IVCSECOND YEAR

Electronics

Engineerin

g

Technicia

n

COMMUNICATION

ENGINEERINGLAB - IMANUAL

STATE INSTITUTE OF VOCATIONAL EDUCATION

DIRECTOR OF INTERMEDIATE EDUCATIONGOVT. OF ANDHRA PRADESH


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Telugu Academy Publication : Vocational Course - fyctec

INTERMEDIATEVOCATIONAL COURSE

SECOND YEAR

COMMUNICATION ENGINEERING LAB - IMANUAL

FOR THE COURSE OF

ELECTRONICS

ENGINEERING TECHNICIAN

STATE INSTITUTE OF VOCATIONAL EDUCATION

DIRECTOR OF INTERMEDIATE EDUCATION

GOVT. OF ANDHRA PRADESH

2005


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Intermediate Vocatioinal Course, 2nd Year

COMMUNICATION ENGINEER LAB - IMANUAL

(For the Course of Electronics Engineering Technician)

Author : Sri. M. Shanmukha Chary

J.L in Electronics,Govt. Jr. College, Malkajgiri, Secundrabad.

Complied by : Sri. M. Shanmukha Chary

J.L in Electronics,

Govt. Jr. College, Malkajgiri, Secundrabad.

Price : Rs. /-

Printed in India

Laser Typeset Reformatted by SINDOOR GRAPHICS, Dilsukhnagar, Hyderabad-60.Phone : 24047464


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CONTENTS

S.No. Chapter Name Page No.s

1. SERVICING TOOLS AND INSTRUMENTS 1 - 6

2. ELECTRONIC LAB SAFETY PRECAUTIONS 7 - 8

3. SOLDERING PRACTICE ON PCB AND WIRING PRACTICE 9 - 10

4. FAMILARISATION OF ELECTRONIC COMPONENTS 11 - 20

5. STUDY OF POWER SUPPLY STAGE IN RADIO RECEIVER 21 - 22

6. STUDY OF OUTPUT STAGE, VOLTAGE MEASUREMENT 23 - 25

7. STUDY OF DETECTOR AND AF VOLTAGE AMPLIFIER 26 - 27

MEASUREMENT OF VOLTAGES

8. IF AMPLIFIER 28 - 29

9. RF AMPLIFIER, MIXER, LOCAL OSCILLATOR 30 - 31

10. STUDY OF FM RECEIVER 32 - 33

11. STUDY OF IC VERSION 2-BAND AM/FM 34 - 37

RADIO RECEIVER AND TAPE RECORDER

12. STUDY OF MULTI BAND RADIO RECEIVER 38 - 39

13. FAULTS IN RADIO RECEIVER 40 - 41

14. PUBLIC ADDRESS AMPLIFIER 42 - 46

15. RECTIFY THE FAULTS IN PUBLIC ADDRESS 47 - 50

AMPLIFIER SYSTEM

16. TAPE RECORDER TWO-IN-ONE AND AUDIO CD PLAYER 51 - 56

17. RECFITY THE FAULTS IN THE TAPE RECORDER 57 - 62

AND TWO-IN-ONE

18. RECTIFY THE FAULTS IN AUDIO CD PLAYER 63 - 84


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1Communication Engineering Lab - I

AIM :

Study of servicing tools and instruments, Soldering Iron, Screw Driver Set, Tweezer, Nose

Plier, Cutter, Hammer, File, Desolder Pump, Squeezer.

Equipment Required :

Servicing Tools, Instruments, Soldering Iron, Screw Driver Set, Tweezer, Nose Plier, Cutter,

Hammer, File, Desolder Pump, Squeezer.

Theory :

Soldering :

It is a method of uniting two or more pieces of metal by means of a fusible alloy or metal called

solder applied in the molter state.

Soldering Iron, consists of insulating handle, connected through a metal shank to the bit. The

bit is made of Iron has got good heat capacity and has good thermal conductivity. Generally some

irons have thermostatic central to keep the temperature of the bit constant wattages 15W, 25W, 50W

and 100 Watts.

The low wattage iron like 5W, 5W are used to assemble components like FETs or MOSFETs

For audio/video circuits 15W, 25W.

For soldering electrical wires 60W, 100W cables which needs a high amount of power

dissipation.

SOLDERING IRONFig 1.1

SOLDERING GUN

Fig 1.2

1. SERVICING TOOLS AND INSTRUMENTS

Insulated feed handle

Filament

Bit

Metal Shank with bit

Soldering Tip

Body

Main Chord


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2

Solder Squeezer :

It is mainly used to suck the molter solder completely at the joints to be desolder in order to

ensure, effective desolder, it consists of a spring placed in a hollow tube with a mechanism to apply or

release force on the spring. Initially the spring is compressed by applying force. When the force of the

spring is released using press release button the spring produces a sucking force through a nozzle

while retaining its original shape. This sucking force can be used to remove the molten solder at the

time of desoldering.

Soldering Gun :

Soldering gun is a soldering tool used for soldering at a given instant heat. High current flows

as long as the switch is pressed. It operates based on the principle of transformer inside the construc-

tion. The primary winding is given to 230V and the secondary winding is given to tip of the soldering.

Soldering Iron Stand :

It is used to place the soldering iron when not in use. They are made of wooden plants, heli-

cally wound iron etc.,

Soldering Alloys :

The solder alloy has low melting point and the liquids at temperatures, below the melting point

of pure lead. The wetting depends on Tin content and the load is added to reduce cost.

Example : Tin lead, Tin antimony and Tin lead, antimony.

Soldering Flux :

Soldering Flux is any solid, liquid or gaseous compound which can be heated is capable of

promoting or accelerating the wetting of metals with solders such medium is called flux.

Wires :

Generally single strand and multi strand wires are used for interconnections for assembling

discrete components, circuits.

Screw Driver :

A Screw Driver is a hand tool, which used to loosen or tighten or to keep the screws in posi-

tion. Its size usually various from 4mm to 600mm.

STANDARD SCREW DRIVER

Fig 1.3

Blade or Handle

Shank

Tip


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Common Screw Driver :

It is used to meet different types of jobs where plenty of room is available and the head of the

screw is out in the open.

THIN Blade Screw Driver :

It is used for screwing or unscrewing the

screws of switches, lamp holders etc.,

Heavy Duty Screw Driver :

It is used for screwing or Loosening heavy screws.

Pliers :

These are used for holding or griping small screws or bolts in position, cutting, twisting andbending the wires.

Insulated Cutting Plier :

It is used for cutting wires, gripping

operation by hand, holding jobs, twisting wires

and a number of other operations in electrical

wiring.

Nose Plier :

As the name implies with a thin nose,

these are used for bending, holding thin wires

and forming eyes of the wires.

Ball Peen Hammer :

It consists of hammer face, which is used

to drive in, nails in to wooden bottom or for gen-

eral work and end for cutting wall plaster and

bricks when it is necessary to take wiring from

one room to another.

INSULATED PLIER

Fig 1.6

Insulated Handle

Pivot

Wire Cutter

Jaw

THIN BLADE SCREW DRIVER

Fig 1.4

HEAVY-DUTY OR SQUARE

BLADE SCREW DRIVER

Fig 1.5

LONG NOSE PLIER

Fig 1.7

BALL - PEEN HAMMER

Fig 1.8

Ball - Peen

Cheek

Eye

Post

Face

Head

Handle


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4

Claw Hammer :

It is used for duel - purpose hammer. It

has one side hammer face, which is used to drive

in nailsor general purpose and claw at other endfor pulling out nails.

Hacksaw :

It is especially designed fool for cutting

metals like conductors, cables etc.,

Wooden Saw or Tension Saw :

It is used for cutting small jobs like

cutting wooden batten, wooden black boards etc.,

Wooden Chisel :

It is used for cutting un wasted wooden

pieces of the wooden boards.

COLD Chisels :

It is used for plaster cutting or far brick cutting.

BALL - PEEN HAMMER

Fig 1.8

Handle

Cheek

Face

Claw

Eye

HACK SAWFig 1.9

Frame

Wing NutHandle

Pin

WOODEN CHISEL

Fig 1.10

Heel Tooth

Toe

BackBlade

Handle

Blade

CuttingEdge

FerruleTangHandle

WOODEN CHISEL

Fig 1.11

COLD CHISELS

Fig 1.12


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Hand Drill machine :

It is used for making holes in wooden

batter, Wooden blocks, Wooden boards etc., to

facilitate the passage of insulated wires.

Scratch awl :

It is very sharp tool, it should be handled

carefully. It is used or making small hole or

impression is made into the wooden before

screwing

Rawl Plug Jumper :

It is used to make holes in stone walls or

concrete walls and should not be used onmetals.

Centre Punch :

It is used for mark the location of holes

to be drilled.

Electrician Knife :

It is used for removing the insulation from the wires.

Files :

Files are used to remove the waste and

rough or burrs on wires and joints etc.,

HAND DRILL

Fig 1.13

Drive Wheel

Main Handle

Jaw

Drill

SideHandle

ChuckPinion

SCRATCH AWL

Fig 1.14

Sharp Point

Handle

RAWL PLUG JUMPER

Fig 1.15

Rawl Plug Bit

CENTER PUCH

Fig 1.16

ELECTRICAL KNIFE

Fig 1.17

Trip

ELECTRICAL KNIFE

Fig 1.18

Face

Length

HeelHandle

TangEdge


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6

Try Square :

It is used for making and checking the angles of 90

Pipe Vise :

It is used for holding the conduits during

conduit cutting or cutting threads or for bending

conduits.

Taps :

It is used for cut internal threads for conduits.

Results : All servicing tools and instruments are studied carefully.

Questions :

1) Name the servicing tools

2) Name the servicing instruments.

T - HANDLE - TAP WRENCH

Fig 1.19


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8

Victim has burns on front side :

Lay the patient as shown in fig. (a), loosen the clothes around the chest and stomache, then

place a pillow or rolled up beneath the patients shoulder, so that his head falls backward.

Now hold the patients head between the knees and draw his hands over his head until they are

horizontal, keep them in that position for about two to three second as shown fig. (a). Next bring the

patient hands on each side of his chest and press inward for about 2 to 3 second as shown in fig (b).

Repeat these two movements 10 to 15 times in a minute. Under any circumstances the process should

not be stopped until the doctor arrives. This method is also known as silvsters method :

Fig 2.3

Fig 2.4

Short Questions

1. What is First Aid.

2. What are the precausion for prevention of electrition.

Essay Questions

Write electric shock treatment processor in the laboratory before reaching treatment for a doctor.


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Aim :

Soldering practice on PCB and wiring practice.

Equipment required :

PCBs soldering iron, lead, paste, components Diodes, Transistor, resistors, capacitors etc.,

Theory :

A Printed Circuit Board popularity known as PCB is a piece of plastic insulating board, on one

side of which a complete layout diagram of an electronic circuit consisting of copper or silver conduct-

ing parts is printed by a special phote engraving process. On the other side of the PCB are mounted

electronic components like resistors, capacitors, coils, transformers, tubes, transistors, diodes, ICs.

Suitable holes are punched in the PCB for mounting the components which are connected to the

conducting paths by soldering. The plastic board is made of a (translucent) transucent material andwith a bright light on one side, the circuit on the opposite side can easily traced.

Printed circuit boards are extensively used for assembling electronic circuits particularly those

using semiconductor devices like transistors and ICs. Use of PCBs makes the circuit assembly also

lends itself efficiently to mass production method.

3. SOLDERING PRACTICE ON PCB AND WIRING PRACTICE

+VCC

VO

RE

Cb

RE

CE

CCR

CR

1

R2

CER

2

CC

R2

TR1

250 mF

220 mF 220 mF

470 W

3.3 K

33 K

RC

5 K

BC 145

1.2 K

5 mV S

SINGLE STAGE TRANSISTOR AMPLIFIER

PCB LAYOUT

COMPONENT PCB LAYOUT

Fig 3.1

Fig 3.2

Fig 3.3


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Q

C

T1

T2

C

r

Q

R

R

R

BE

E

CB

R

C

Aim :

Study of push pull amplifier and measurement of output voltages


CRO, Multimeter, Soldering Iron 25W, lead, flux,Screw Driver Set, Audio Amplifier.

Theory :

A class B push pull amplifier is used in audio output stage. The output of the amplifier signal

is in the audio frequency range 20Hz to 20KHz. In any communication system we can hear the speach

300Hz - 3400Hz range called voice frequency. The amplifier which is operated in the above range is

called audio frequency amplifier.

The distortion in the audio output is called audio effect common faults in audio section in thetransistor radio receiver as floows.

S.No. Symptoms Possible Cause Remedies

1. Poor Sound Collector Voltage of transistor Compilling capacitor short

below of leaky check base and

ground voltage

2. Hum Transistor terminals are Use shielded

not properly shielded.

3. Intermittent Coupling capacitor may Replace capacitor and

Output open intermittenly volume check volume control

control defective

4. No Output All voltages across the Check power supply

trnasistor leads are dead.

PUSH PULL AMPLIFIER

Fig 6.1

6. STUDY OF OUTPUT STAGE, VOLTAGE MEASUREMENT


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Noise :

If voice coil rubs the body of the speaker cracking noise will be produced, may be core paper

broken and there will be no change in voltage / current data.

Loud Speaker :

A loud speaker with high fidility in AM/FM receivers. When voice coil open no effect on

voltage data. IC get overheated, replacement is only one remeady.

Common Troubles in the Audio Circuit :

Distortion :

This occurs by in proper biasing due to an open resistor. Defective transistor lack of heatmeasure voltage at th eemitter junction.

Low Volume :

Open bias resistors or defective transistor. Measure Voltage / resistances in the stage. Defec-

tive components may be replaced.

Receiver dead :

No supply to the output transistor pair or output IC due to open PCB track.

Open driver Transformer :

Power transistor of the receiver with normal voltages resulting voltage amplifier reads zero

voltages.

Open emitter resister :

Open emitter resistor RE results a dead receiver. Check the resistances and voltages levels are

trouble.

Coupling Capacitor :

If the coupling capacitor open results the receiver is in dead mode. If it is leaky the output is

distorted. If it is short the produces excessive distortion.

Volume Control / Tone Control :

Noisy volume or tone control is to be replaced


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Table :

S.No. Voltage on transistors collector output Voltage on RL

Speaker AF

T1

T2

voltage

Results :

Studied power output stage of a Radio Receiver

Question :

1) Write the different faults in audio output stage.

2) Write servicing procedure of audio output stage.


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26

Aim :

Study of Detector and AF Voltage Amplifier Measurement of Voltages


Experimental board, CRO, Multimeter,

Theory :

A transister radio receivers makes a use of semiconductor diode in the detector stage. The

diode has same propecties as detection and rectification.

The diode is used for AM detection / demadulation. In the given circuit, C is a small capacitence

and R is a large resistance. The parallel combination of R,C with load resistance across RL the output

voltage is measured VO. At each positive peak of RF cycle, C changes upto a potential almost equalto peak signal voltage Vs. The output produced VO is modulating voltage with small amount of

ripple. In practical circuit unwanted signals are removed by using diode detector.

The audio signal from the detector is fed to the base of the voltage amplifier through a coupling

capacitor C11(8PF), Resistors R12, R13 are the voltage dividers for the base emitter bias. Resistor

R14 is the dc stabilizer by passed by the capacitor C13 (20mF), C14 (0.005mF) is the RF by pass filter.

C12 (30mF) is an electrolytical capacitor and is shunted across the battery supply for decoupling

signals from all stages.

DETECTOR

Fig 7.1

Procedure :

1. Switch on the demonstration board by connecting the power cord to the AC supply

2. Observe the carrier and modulating signal to the modulator circuit

3. Connect the carrier and modulating signal to the modulator circuit

4. Observe the amplitude modulated wave in synchronization with the modulating signal in the dual

trace CRO.

7. STUDY OF DETECTOR AND AF VOLTAGE AMPLIFIER

MEASUREMENT OF VOLTAGES

IFT2

R

R

R

Q OA79

CAVC

Q IFT3

To AF Amplifier

C


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5. Then give the AM output to the input of th edemodulator.

6. By adjusting R,C values we get minimum distorted modulating signal.

7. Campare the amplitude and frequency of demodulated output with original modulating signal.

8. Measure output voltage Vo.

Table :

S.No. Voltage on detector Demodulated AF power AF Transformer

OA79 output voltage transistor voltages secondary

VCE

VBE

voltage

Result :

AM Detector, Voltage amplifier stages are studied measured voltages.

Questions :

1) Name the working principles of AM detector.

2) What is the use of voltage amplifier.

Aim : To study of Multiband Radio Receiver


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30

Aim :

Study of RF amplifier, Mixer, local oscillator stage and voltage measurement.


A radio receiver, AC voltmeter and connecting wires.

Theory :

RF AMPLIFIER

Fig 9.1

RF Stage :

The desired RF signal selected by the tuned antena circuits is applied to the input of the radio

frequency amplifier. After amplification from the RF stage, the modulated RF signal passed on to the

next stage i.e. converter stage. The stage functions are

1. It increases the sensitivity of the receiver because of additional amplification.

2. It improves the selectivity of the receiver due to additional tuned circuits.

3. It eliminates the image frequency interference

4. It reduces the noise level because of a stronger signal fed to the converter stage.

5. It improves the AVc action.

The two transistors are used to a mixer and a local oscillator stages perform the function of the

mixer. The signal from the ferite antenna coil L1 is fed to the base of the transistor Q1. Resistors R1

(6.8K) and R2 (39K) form a voltage divider across the battery for the emitter base bias. Resistor R3

(3.3K) in the emitter lead is a dc stabilizer. The oscillator coil is L2 and it feeds its local oscillations to

the emitter of Q1 through capacitor C3. The tuning and oscillator capacitors aere ganged in the re-

ceiver. The station signal to the base and local oscillator signal to the emitter mix to produce, the

modulated IF signal at the collector which applies it to the IF transformer. Capacitor C2 (0.02mF) is

9. RF AMPLIFIER, MIXER, LOCAL OSCILLATOR

Antenna

Converter

R1

C1

R2

R3

L1

C3

C2C

4 C5

C6

_ +

Battery


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an IF decoupling capacitor to prevent IF signals from being fed back to the base. Taps are used to

oscillator coil and the IF transformer coinding for impedance matching Q1 is PNP transistor in which

the collector is at a negative potential with respect to the base.

Procedure :

1) Connect the dc power supply

2) Measure collector to emitter voltage of R.F stage

3) Measure base to emitter voltage of RF stage.

4) Measure oscillator voltage VeE.

5) Measure mixer stage output voltage.

Table

S.No. RF Voltage RF output Voltage Mixer output

VBE

VCE

voltage

Result :

RF, oscillator and mixer stage voltages are measured with ac/dc voltmeter.

Questions

1. Write RF voltages

2. Write testing processor of RF amplifier, local oscillator and mixer stages


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32

Aim :

Study FM Radio Receiver

Equipment needed :

FM Radio Receiver kit, Multimeter

Theory :

FM broad cast radio receivers operates 8 MHz to 108 MHz in band II. Within this band,

allotted frequencies are spaced 200KHz apart and allowed a maximum frequency deviation of 75KHz

around the carrier frequency. Propagation at VHF is restricted to line of sight and coverage is usually

only for a radius of 50KM around the transmitter location. The programmes broad cast on these

channels in the past have been mostly music and the basic modulating frequency band width is 15KHz

as opposed to the 5KHz used on AM stations.

10. STUDY OF FM RECEIVER

FM RADIO RECEIVER

Fig 10.1


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Figure shows the block diagram of a typical FM broadcast receiver. It is a supernetero dyre

circuit with a tuned RF amplifier so that maximum signal sansitivity is 1 to 10mV. The RF stage tuned

circuits and local oscillator are tuned by a three ganged variable capacitor controlled from a panel

knob. The oscillator frequency can be varied from 98.7 MHz to 118.7 MHz. Yielding an intermediate

frequency of 10.7 MHz.

The IF amplifier section if several high gain stages, of which one or more amplitude limiters.

The high gain non limiting input stage, followed by one amplitude limiting stage. All stages are suned

to give the desired band pass characteristics this is centered on 10.7 MHz and has a 180 KHz band

width to pass the desired signal. Amplitude limiting is usually arranged to have an on set throshold of

about 1mV at the limiting - stage input, corresponding to the level of input signal. Which may be set

at 10mV or lower.

The FM detector is used to detect the audio signal.

Procedure :

Connect the dc supply to the FM Receiver tune gain capacitor to reach station frequency

programme comes from the loud speaker.

Result :

FM Radio receiver studied.

Questions

1. Study the FM receiver block wise operation. Write testing processor


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32

Aim :

Study FM Radio Receiver

Equipment needed :

FM Radio Receiver kit, Multimeter

Theory :

FM broad cast radio receivers operates 8 MHz to 108 MHz in band II. Within this band,

allotted frequencies are spaced 200KHz apart and allowed a maximum frequency deviation of 75KHz

around the carrier frequency. Propagation at VHF is restricted to line of sight and coverage is usually

only for a radius of 50KM around the transmitter location. The programmes broad cast on these

channels in the past have been mostly music and the basic modulating frequency band width is 15KHz

as opposed to the 5KHz used on AM stations.

10. STUDY OF FM RECEIVER

FM RADIO RECEIVER

Fig 10.1


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Figure shows the block diagram of a typical FM broadcast receiver. It is a supernetero dyre

circuit with a tuned RF amplifier so that maximum signal sansitivity is 1 to 10mV. The RF stage tuned

circuits and local oscillator are tuned by a three ganged variable capacitor controlled from a panel

knob. The oscillator frequency can be varied from 98.7 MHz to 118.7 MHz. Yielding an intermediate

frequency of 10.7 MHz.

The IF amplifier section if several high gain stages, of which one or more amplitude limiters.

The high gain non limiting input stage, followed by one amplitude limiting stage. All stages are suned

to give the desired band pass characteristics this is centered on 10.7 MHz and has a 180 KHz band

width to pass the desired signal. Amplitude limiting is usually arranged to have an on set throshold of

about 1mV at the limiting - stage input, corresponding to the level of input signal. Which may be set

at 10mV or lower.

The FM detector is used to detect the audio signal.

Procedure :

Connect the dc supply to the FM Receiver tune gain capacitor to reach station frequency

programme comes from the loud speaker.

Result :

FM Radio receiver studied.

Questions

1. Study the FM receiver block wise operation. Write testing processor


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34

Aim :

Study of IC version 20Band AM/FM Radio Receiver

Equipment needed :

IC version 2-Band AM/FM Radio receiver and tape recorder and multimeter.

Theory :

The kit circuit consists of IC Version 2-Band AM/FM Radio Receiver and Tape recorder In

AM receiver again there are two bands i.e. mediumwave and shortwave. The shortwave frequency

range 535 KHz - 1605 KHz. The FM receiver has frequency band width of 88 MHz to 108 MHz.

The tape recorder, tape transport mechanism and panel controls of tape recorder.

The fault finding procedure of National Panasonic Radio Cassette Model : RX - 1409T.

Set dead, No Play - Back :

Ac socket, mains transformer T5, dc socket J4 open, D5, D6 (IN4002) openor short, leaf switch

open, select switch S2 defective, mPC 1213C short, switch S4, Coip L7, motor or its connection, C76

(100mF), Loose cantact or dry solder, check print.

Play back O.K., No Sound :

Supply to IC 402 missing, R72 (47) R73 (100), R61 (6 80), R67, R70 (2.2K), R68 (18K), R57

(1M) open, C59, C53, C67 (1MF/50V) C73 (470MF) open or short, Q2, Q3 (2SC1684), 1C2

(mPC1213C) defective, speaker or its connection open, head connection wire open, recording switch

open, C72 (47MF), C71 (220MF) VR2 (10K), C67 (1MF/50V), C69 (47MF), C48 (0.001 MF), loose

contact or dry solder, check print.

Low Sound :

Less or abnormal supply voltage, R75 (33), R63 (3.3K) open, C70 (33MF/10V), C67 (1MF/

50V), C60 (0.33MF/50V) short, IC2 (mPC 1213C) faulty, extra speaker socket short, R/P head weak

or misadjusted, speaker faulty, also check, C75 (1000mF), C71 (220MF), VR2 (10K) R70 (2.2K), C63(220MF), R72 (47) C66 (470 MF), R73 (100), R61 (680), R68 (18K), C55 (47MF), C53 (1MF/50V),

Q2,Q3 2SC (1684) and related parts, dry solder, check print.

Humming Sound :

C75 (1000MF/10V), C66 (470MF/10V) open C76 (100MF), IC2(mPC1213C) recording switch

faulty, dry solder, check print.

11. STUDY OF IC VERSION 2-BAND AM/FM

RADIO RECEIVER AND TAPE RECORDER


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Distorted Sound :

Fault due to Mechanism :

R/P head misadjusted, pinch roller, fly wheel, clutchpully, moter and its pully, belt, capstain,

rod just on speaker paper core torw or head or speaker defective, dust accumlated on speaker paper

core.

Faults Due to Electronic Circuit :

Less abnormal supply voltage, C67, C53, C59 (1MF/50V), C73 (470MF/63V), C60 (0.33MF/

50V), C5A (47KPF), loose contact in recording switch or Tape/Radio selector switch, speaker paper

core tornor hard or speaker faulty, dust accumulated on speaker paper core, also check C72 (47MF),

C71 (220MF), R75(33), C70 (33MF), C65 (0.001MF), C69 (47MF), C75 (1000MF), IC2 (MPC1213C)

and its related parts, Q2-Q3 (2SC1684) and its related components, loose contact or dry solder, check

print.

Play back is normal but no recording :

R/P head weak, S3, R/P switch defective, R55(2.2K), R74 (220E), R53 (4.7K), R68 (8.2K)

open, C51(0.047mF), C52 (0.022mF), open or short, MIC socket or condensor or MIC open, loose

contact or dry solder, check print.

Disterbence in Recording :

C62 (0.068mF), C57 (100mF/63V) D1 (MA150) open or short, Q1 (2SC1684) and its related

components, loose contact or dry solder, check print.

Normal sound at low volume level but distorted output when volume increases :

Low supply voltage or low current, check for excess current to motor, high tension in pinch

roller, belt is tight, week battery, mains transformer, C76 (100mF/10V), C75 (1000mF/10V), C66

(470mF/10V), D2 (MA1051) Zener diode, IC1 (AN7220), IC2 (mPC1213) defective check print.

Tape function is OK, but Transistor band is not working :

R3, R8, R9 (47), R1 (2.2K), R2 (100E) open. C19 (0.1mF), C23 (1mF/50V), C16, C22(0.22mF)

C18 (0.047mF), CF1, C13 (47RPF), Ist IFT, IC1 (AN 7220) open or short, S1 band switch defective

D2 (MA1051) short.

AM Band not working :

L2, L4, CT4, C4(7PF), CT6, C6(360PF), C26(12PF), AMOSC, Selecti S1 switch defective.

SW Band not working :

L8, L5, L1, C3 (12KPF), CT2 C8 (10KPF), C7 (0.0015mF), CT3, SW OSC. Coil defective, S1

band switch defective, loose cantact, dry solder check point.


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36

AM-FM RADIO TAPE RECORDER

Fig 11.1


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FM Band not working :

L1, L3, L6, CT1, C10 (7PF), C2 (47KPF). Select switch S1 defective, C9 (0.047mF) FM

Oscillators, Coil, loose contact dry solder, check printer.

Distorted sound of Transistor Band :

Ist IFT, or oscillator coil mistuned, CT trimmer, loose contact in band switch S1, CV1, CV2,

gang capacitor short R5 (47K), R6 (2.2K) open, C16 (0.22mF) C15 (10mF/16V), C12.

Result :

IC vertion 2-band radio AM/FM radio receiver block wise operation is studied.

Questions

1. Study the given IC version 2-band AM/FM radio receiver. Write testing processor


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38

Aim :

To study of Multiband Radio Receiver

Equipment needed :

Multiband Radio Receiver kit, Multimeter and tool kits.

Theory :

In the multiband Radio Receiver RF coil band switches are different remaining stages are same

as in the case of superneterodyre receiver. The frequency band or the wave band covered is decide by

the inductance of the coil and the capacitance of the variable capacitor that tuned circuits in the an-

tenna section and the oscillator section of the converter stage. In modern superheterodyne receivers it

becomes neccessary to have a shortwave bands in addition to the mediumwave (MW), so that stations

broadcosting on SW frequencies can also recieved. A receiver which includes one or two SW bandsalso in addition to the MW band is called multiband Radio receiver.

One coil and a variable capacitor can be tuned over one band of frequencies. For a second

band of frequencies. For a second band of frequencies, a different number of a tunes is required both

for antenna section and the oscillator section of the converter stage. The variable capacitors, which are

parts of a two gang capacitor will remain the same. Thus for changing one wave band to another, one

set of coils and trimmers should be connected to the circuit, simultaneously in the antenna section and

the oscillator section of the converter stage of the receiver. This involves a number of switching

operations that must be performed before a waveband can be changed. This is done with the help of a

special multicantact switch known as the band change switch or a wave change switch. The common

most switch used in multiband receivers is rotary switch.

Rotary Switch :

A rotary band switch consists of moveable contacts and fixed contacts are called positions.

The number of positions per pole is equal to the number of wavebands in the nultiband receiver.

Fixed contacts MW, SW1, SW2 are punche don a circular plate of fibre or some other suitable

insulating material. A smaller circular plate of the same insulating material carrier two semicircular

metalic strips with projections on one end, which will make contact positions MS, SW1, SW2 one by

one as the inner fibre plate is rotated with a central shaft. The fixed poles P1 and P2 punched on theouter fibre plate remain permanently in contact with their respective number of strips.

12. STUDY OF MULTI BAND RADIO RECEIVER


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Procedure :

Check the stages as per the circuit and block diagrams measure the voltage data at each stage.

Result :

Multiband radio receiver stages are identified and found in working condition.

Questions

1. Study the given the multi band radio receiver. Write block wise operation


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40

Aim :

Mension the faults in Radio Receiver and observe the effects on voltage data and performence

of the radio receiver.

Equipment needed :

AC multimeter, radio receiver kit, power supply and connecting wires.

Theory & Procedure :

General faults identified in radio receiver as follows

1. low sound of Radio Band

2. Shortwave working but MW is not working

3. Disturbed and booming sound of radio band4. Normal sound at low volume level, but distorted output when volume increases.

5. AM band is not working.

1. Low Sound of Radio Band :

Due to misalignment of IFTs and related stages components detection diode (OA79) and re-

lated components loose contact or dry solder, check print.

2. SW working but MW is not working :

This problems occurs when band switch point open at MW band position. Properly contact

position should be adjusted to switch position, MW oscillator, MW antenna coil open, moisture on

MW oscillator coil, loose contact or dry solder, check print of PCB.

3. Disturbed and booming sound of Radio Band :

This problem comes when gang capacitor is connected loosly, trimmer loose, band switch

loose, oscillator crip or IFT instable or loose contact or dry solder, check print of PCB.

4. Normal sound at low volume level, but distorted output when volume increases :

Low supply voltage or low current, check for excess to motor, high tension in pinch roller, belt

is tight rectifing and filter circuit components failure, weak motor, loose cantact, dry solder, check

print, low sound occurs for defects.

5. AM band is not working :

Defects in coils and gang capacitor, select switch S1 defective band switch, loose contact or

dry solder, check print of PCB.

13. FAULTS IN RADIO RECEIVER


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BLOCK DIAGRAM OF FM RADIO RECEIVER

Fig 13.1

Results :

Stage wise voltages are measured and found the kit is in working condition.

Questions

1. Mension the faults in Radio Receiver block wise. Write rectification processor

RF

tunedamp

Gangcapacitor

Auido10.7 MHz with 180 KHz

bandpass

88-108

MHz

speaker

Audio

amplifierVaractor

trimmer

Volumeand tone

control

AFCDelayedAGC

detector

Localoscillator

De

emphasis

Antenna

Disc

riminator

IFtuned

limitingamp

IF

tunedampMixer

98.7 - 118.7MHz


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42

Aim :

Study of Public Address System, Microphone, Amplifier and loud speakers and inter

connections.

Equipment needed :

3 Microphones, 2 loud speakers and 100W amplifier kit, connecting wires, multimeter.

Theory :

A public address system amplifies low level sound to a higher level so that it can be heard by

large number of people gathered and at a considerable distance.

A basic public address system has input source is a microphone, which pick ups low level

sound like a human speech. Examples of some other input sources are a cassette player for playbackof recorded music, or compact disc player.

Amplifier :

It is an electronic circuit in which sound low level signal to higher level signal and improves

the signal gain. The gain depends upon the number amplifiers are used in casteded stages. This

determines the AF power levels. This amplifier consists of 3 or 4 microphone auxillary circuit at input

level with controlling switches for each microphone. Each microphone has got volume controllers to

control audio signal levels.

Special electronic circuit provides and excellent sound quality. Cut and Boost type Bass and

Treble controls, master control, 4 input volume controls and a special feature of adjusting tape sensi-

tivity through tape Hi/Lo switch have been provided. An LED ARRAY gives a visual indication of the

output level. Line ouput in addition to speaker outputs of 4,8,16 ohm and 100W is provided.

FRONT PANEL CONTROLS OF AN AMPLIFIERFig 14.1

Specifications

Player Section :

Track system : 2 Track Monaneal

Tape speed : 4.75 Cm/Sec

FF/Revind Time : 190 seconds with C.60 tape

Tape speed accuracy : within +2% - 1%

Wow and flutter : 0.35% Nominal

14. PUBLIC ADDRESS AMPLIFIER


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MICRO PHONE - SPECIFICATIONS

Fig 14.2


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SPEAKER CONNECTIONS :

Speaker impedence taps of 4, 8 and 16 have been provided for direct connection of speakers to the

amplifier when the distance between the amplifier and speakers is less than 50 meters. Use 23/26 or

thicker cable for connections. Be sure that the total impedence of the speakers is equal to or more than

the impedance specified on the terminal strip.

SPEAKERSFig 14.3

PHASING OF LOUDSPEAKERS / UNITS

When two or more speakers / units are installed in the same area and are facing in the same

direction, it is essential that their cones / diaphragms move in unison. Otherwise, the sound output of

one speaker will cancel the sound output of other. To avoid any mistake, the terminals of all driver

units are marked L1 & L2. For correct wiring refer the sketches.

PAS CONNECTIONS

Fig 14.4

BAD

GOOD

GOOD

GOOD

GOOD

BADGOOD

GOOD

GOODGOODGOOD

BAD

Even if any one of the equipment or item is of

poor quality, the sound quality will be bad.


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46

WARNING :

Connect a set of speakers to EITHER any ONE of the low impedence taps 4 & 8 or 16 or to

100V line output. Do not use more than one speaker output connection at a time.

AMPLIFIER CONNECTIONS

Fig 14.5

Result :

PAS is assembled in college ground observed sound distribution throught the ground in public

meeting.

Questions

1. Study the block wise operation and specification of public address system

2) Methods of testing further IF, Cd remains loaded in deck but play does not takes place.


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Aim :

Rectify the faults in public address system.

Theory :

A Public address system amplifies low level sound to a higher level so that it can be heard by

large number of people gathered and at a considerable distance.

The PAS consists of microphone, amplifier and loud speaker

Even if any one of the equipment or item is of poor quality, the sound quality will be bad.

A good quality, trouble free and satisfactory performance. Use good quality cable and connec-

tion with good connections which will give good and satisfactory sound.

Connections of the Loud Speaker :

This is very impartent. Wrong connections can be damage both the amplifier or loud speaker.

Improper connection lead to poor quality of sound as well.

It is a specifications of a loud speaker which is very impartent to know for correctly connecting

loud speakers to an amplifier of 8, 16, 4

We can connect the more than one loud speaker in series or parallel combination

If the loud speakers are connected in series see effective impedence R = R1 + R2 should be

equal to the output impedance of the amplifier. If the speaker are connected in parallel R = see the

impedence offer by the output terminals of this amplifier.

Impedence Matching :

To transfer maximum power from amplifier to loud speaker the output impedence of th eamplifier

is should be equal to the impedence of the good speaker.

A 23/26 type cable is prefarable to use - 100W amplifier. The distance between amplifier to

cable is 20 metres to reduce power losses in the cable. For efficient transfer of power from the ampli-fier to the speaker, we can avoid power losses by using line matching transformer (LMT).

The terminal strip with making are used for connecting conbination of low impedence speak-

ers or drive units (without LMT) with impedences such as 4, 8, 16

The terminal strip with V (Volt) marking are used for connecting speakers / driver units with

LMT.

15. RECTIFY THE FAULTS IN PUBLIC ADDRESS AMPLIFIER SYSTEM


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SPEAKER INTER CONNECTIONS

Fig 15.1


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AMPLIFIER CIRCUIT IC VERSION

Fig 15.2


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50

LMTs are used in a large installation which require a large number of speakers to be

connected at a distance. As the length of the cable increases so the strength of the sound signal

decreases. Hence in installations where the length of the cable is sub stantial. LMTs are used. When

using LMTs 100V, line is used. This 100V line system comparable to the electricity distribution

system. In electricity distribution system a large voltage is transmitted from the sub-station such high

voltage is trnasmitted to over come losses in cables over large distances. This voltage being is sup-plied to houses is reduced by using a step-down transformer. Similarly a high voltage signal 100V. is

fed to LMTs These LMTs act as step down transformers. As the electricity wiring system in houses

is done in parallel similarly all the wiring when using LMT is done in parallel.

The Bass CONTROL of the amplifier should be in CUT position when Driver Units / Horn

speakers are used with the amplifiers.

Always check PHASING while connecting the driver units.

Always earth the amplifier before operation connect the earth terminal of the amplifier to the

electrical earth / any water pipe.

Result :

Faults in PAS is studied.

Questions

1. Mention the faults in public address system. Write rectification processor


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Aim :

Study of tape recorder, two-in-one and audio CD player

Tape Recorder :

It is an electronic and tape transport mechanism in which a magnetic tape is recorded music or

speech

The tape recorder consists of following controls.

A tape recording machine is required to perform three important functions viz. recording,

playback and erasing. Fig is a block diagram which indicates the basic functions performed by a tape

recorder system.

In the block diagram, the same amplifier is used for recording and playback and is called therecord/playback amplifier. During the recording process a ganged switch connects the input of the

amplifier to the microphone and the output is connected to the record head so that the amplified audio

signals are impressed on the moving tape. In the playback position, the magnetic signals picked up or

detected from the tape by the same head are applied to the input of the amplifier for reporduction by

the loudspeaker. One and the same head performing the combined functions of recording and playback

is known as the record playback head. The tape is wound on the supply reel and is moved at constant

speed and under constant tension in front of the record / playback head during recording and playback

operations. The tape is finally collected by the take-up reel.

An erase head located to the left of the record/playback head wipes off any information from

the tape before the tape reaches the record head for a fresh recording. The erase head is energised by

the HF oscillator which also applies an AC bias to the record head during the recording process for

improving the quality of recording. The erase h ead is not energised ruing the playback process to

prevent the recorded matter from being erased. A tape transport system consisting of a motor, drive

assembly, belts and pulleys enables the tape to move at constant speed during record and playback

process and also to move faster during the fast-forward and rewind processes.

TAPE TRANSPORT MECHANISM

Fig 16.1

16. TAPE RECORDER TWO-IN-ONE AND AUDIO CD PLAYER

Takeup Real

Drive Belt

Tape

Pinch Roller

Capstan

Fly Wheel

Motor and

Fan

IdlerDriveSupply Reel

Bus Idler

Brake Shoe

Tape Guide

Erase Head

Record /Playback Head

Pressure Pad

RubberisedIdler Wheel


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52

TAPE CIRCUIT

Fig 16.2


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1. ON/OFF switch

2. Volume control

3. Play press button

4. Rewinding

5. Fast Forward button

6. Recording

7. Eject / Stop

8. Pause.

All above are called operating controls of a tape recorder. The tape transport mechanism and

motor recording / play back heads, cassette and electronic circuit, which operates in recording / play-

back mode of operation.

Two-in-one :

In this system a radio and tape recorder is separated by a lever switch. In the circuit taperecorder operation is same. Radio operation as follows

A transistor/IC version receiver is like any other normal receiver in which valves have been

replaced by trannsistors. With the use of transistors, the size and weight of all other components

required for the circuit is also considerably reduced. Thus, reasonably prices pocket transistor receiv-

ers are not available in all convenient shapes and sizes.

Except for some receivers meant ot receive only local stations, all other modern transistor

receivers are of the superheterodyne type. A transistor superheterodyne receiver makes use of the

stages which function in the same way as the stages of a valve type receiver. However, there are

certain differences in the circuits employed in the two cases because of some basic differences be-tween the properties of transistors and vacuum tubes. In order to bring out clearly the points of differ-

ence and similarity between the circuits used in the two types of receivers, the circuit diagram of a

standard transistor receiver.


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54

TWO IN ONE

Radio Cassette Recorder

Fig 16.3

CD Player :

A recorded compact disc (CD) is played in a CD/VCD player, detection of pits and present on

the CD is also done by a laser beam of low power are focused on the rotating CD. If the rays reach a

flat they will come back after reflection from the flat, but if fail on the PIT then they will get absorbed

there and will not come back. By processing to reflected rays circuits of CD/VCD player get informa-

tion about the combinations of PITS and FLATS. On these digital signals thousands of circuits of CD/VCD player do various type of processing and finally generate analog audio / video signals. Similar to

those signals which were given at the input of the video card. By giving audio signals to the loud

speaker and video signals to video section of a T.V, sound /picture similar original can be produced.

1. CD player speed during recording / play back speed is 2.5 cm/second. A C.D. consists of a outer

diameter of 120mm. The aluminium coating present on the CD is 116mm diameter inner diameter of

50mm, a CD consists of a hole with diameter is 15mm. The recording is done on thousands of spiral

tracks present on this 33mm wide ring. The CD thickness about 1.2mm. on CD can store 800MB of

audio/video programme. With a duration of 1 hour.


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CD PLAYER FUNCTIONAL DIAGRAM

Fig 16.4

METHOD OF TEST-

ING LENS UNIT

DIRECTION OF

MOVEMENT OF

LENS DURING

TESTING


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56

2. Thousands of tracks are present on the 33mm wide ring. A gap is maintained between two nearly

tracks on these tracks of a laser beem is focused.

3. A high power laser (Light Amplification by stimulated emission of radiation) used during CD

writing. A low power laser beam is used for playback.

4. Laser rays are nothing but a beem of light.

5. CD can be cleaned with soap water.

6. On CD when scratches are formed, play is not possible.

7. A digital signals are two voltage levels ie. 0V, 3V.

8. CD recording is done on the inner most track and the last part of the programme is recorded on the

outer tracks.

9. On a CD in between audio / video signals sync, timing signals are present.

Result :

Tape Recorder, Two-in-one and Audio CD Player kit wise operation is studied

Questions :

1. What are the operating controls of tape recorder. Explain function of each one

2. Study the Two-in-one. Write working

3. Study the CD Player. Write working

CDFig 16.5


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Aim :

To study the faults in the tape recorder and Two-in-one.

Equipment needed :

Tape recorder kit, Two-in-one kit and multimeter, servicing tools and instruments.

Tape recorder fault finding Processor:

BPL SANYO Stereo Cassette Recorder Model : C2010

Set Dead, No Play-Back :

Mains lead, transformer T1 (0.7.5V/500mA) open, D1-D4 (1N4007) open or short, leaf switchnot connected, C62 (2200MFd), IC102 (TA7769) short, motor open or short, dry solder, check print.

Play-Back OK, No Sound, No Audio :

Headphone socket defective, C56, C59 (330MFd/10V), IC102 (TA7769), speaker or its con-

nection open, C57, C58 (0.1MFd), C61 (220MFd) short, C55, C60 (47MFd), loose contact or dry

solder, check print.

Play-Back OK, No Sound, Audio OK :

Q101 (2SC1815) open, D5 (6V-zener) short, R50 (220W ), R18 (22W ), C6, C15 (10MFd) open,

IC101 faulty, recording switch open, shield wire of head connection open, VR103, VR203 (50K)

faulty, also check : C51, C52 (1MFd:63V), C9, C12 (47MFd), C7, C13 (39KPf), R10, R21 (3K9), R8,

R28 (4K7), R9, R29 (10K), loose contact, dry solder, print open.

Humming Sound :

Recording switch faulty, C62 (2200MFd), C50 (220MFd), C61, C11 (1000MFd), C14 (47Mfd),

C8 (33MFd), ground wire of chassis open, dry solder, check print.

Low Sound :

R/P head weak or misaligned, less or abnormal supply voltage, C9, C12 (47MFd), R17, R19

(82K), R18 (22W ), R52-R53 (33W ), C53, C54, C55, C60 (47MFd), IC102 (TA7769) faulty, D6-D8

(IN4148) short, speaker voice coil defective, also check : C58 (0.1MFd), C59 (330MFd), R56 (270W ),

C61 (220MFd), C51-C52 (1MFd), VR103-VR203 (50K), R54 (270W ), C56 (330MFd), C57 (0.1MFd),

C11 (100MFd), IC101 & its related parts, dry solder, check point.

17. RECFITY THE FAULTS IN THE TAPE RECORDER

AND TWO-IN-ONE


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58

RADIO TAPRE RECORDER IC VERSION

Fig 17.1


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Distorted Sound :

Faults Due to Electronic Circuits :

Speaker paper cone torn or hard or speaker faulty, less or abnormal supply voltage, tone con-

trol VR102, VR202 (50K), volume contro VR103, VR203 (50K), C51-C52 (1MFd/63V), C6, C16(10MFd/16V), C9, C12 (47MFd), C8 (33MFd), loose contact in recording switch, also check : C58

(0.1MFd), C57 (0.1MFd), C60 (47MFd), R56 (270W ), C61 (220MFd), C57 (0.1MFd), C56 (330MFd),

C55 (47MFd), IC102 (TA7769), IC101 & its associated parts, loose contact, dry solder, check print.

Faults Due to Mechanism :

Pinch roller, flywheel, motor and its pulley, bush, capstan rod, glinder, clutch pulley defective.

Play-Back is Normal But No Recording :

Recording switch at record mode position open, R/P head weak, R5, R15 (5K6), R6, R25(2K2), C3, C16 (1MFd/63V), C2 (0.22MFd), C17 (22Pf), condenser mic faulty, print open.

Normal Sound Low Volume Level But Distorted Output when Volume Increases :

Low supply voltage or low current excess motor current, high tension in pinch roller, belt is

tight, D1-D4 (IN4007), C62 (2200MFd), D5 (6V-zener) open, C11 (1000MFd), Q101 (2SC1815)

faulty.

Distrubance in Recording :

R2 (680W ), R3 (33K), C5 (0.47Mfd), R4 (12K), C4 (82Pf), R26 (1K8), R277 (33K), D7-D8

(IN4148), recording switch defective, loose contact or dry solder, check print.

Any one Channel Sound Normal (Left or Right) but Distorted Sound on other Channel (Right

or Left) :

R/P head weak or misaligned, check volume control and its related pats, IC101 & its related

parts.

Two-in-one :

Faults and Rectification of Bush Radio Cassette Tape-Recorder Model : MRK 5800

Set Dead, No Play-Back :

AC socket, leaf switch open, TAPE/RADIO selector switch not connected, T101 (mains trans-

former) open, D8D-11 (4 x IN4001) open or short, L17 open, C46 (640MFd), C38 (1000MFd) short,

motor open or short, loose contact or dry solder, check print.


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Play-Back OK, No Sound, No Audio :

R30 (39W ), R31 (180W ), D1 (CD2A), R29 (100W ), R26 (2K7), R25 (680K) open, C29 (1MFd),

C33 (1000MFd), earphone socket open, TR5, TR7 (BC148) open or short, TR9 (AC187), TR10

(AC188) open, speaker or its connection open, R32 (68W ), R33 (27W ), C25 (1MFd), C36 (250MFd),

dry solder, check print.

Play-Back OK, No Sound, Audio OK :

Recording switch point at palyback mode position open, R19 (680W ), R12 (100K), R16 (2K7),

R8 (15K), R9 (100W ), R17 (1K2), C9, C15 (5MFd) open, C10 (2000Pf), C11 (1000MFd) short, TR1,

TR2 (BC148) open or short, RV3 (10K) open, wire of head connection open, loose contact or dry


Low Audio Output :

Less ore abnormal supply voltage, C38 (1000MFd), TR9 (AC187), speaker voice coil short orspeaker defective, earphone socket defective, C36 (250MFd), C33 (1000MFd), TR9 (AC187), TR10

(AC188), R33 (27W ), R32 (6b8W ), R30 (39W ), R31 (180W ), D1 (CD2A, TR7 (BC148B), C29 (1MFd),

R29 (100W ), R26 (2K7), R25 (680K), TR5 (BC148B), C25 (1MFd), C51 (0.1MFd), C24 (1000MFd),

RV3 (10K), loose contact or dry solder, check print.

Audio OK, Low Sound :

R/P head weak or misaligned, R21 (2K2), C15 (5MFd) short, TR2 (BC148) & its related

components, C11 (1000MFd), R19 (680W ), R8 (15K), R16 (2K7), value of R17 (1K2) developed,

C16 (47MFd), C12 (600pf), R12 (100K), TR1 (BC148B) & its related components, R9 (100W ), C10

(2000Pf), C9 (5MFd), loose contact, dry solder, check print.

Distorted Sound : Faults Due to Electronic Circuit :

R/P head weak or misaligned, loose contact in recording switch, speaker paper cone tron or

hard or speaker faulty, dust accumulated on speaker paper cone, less or abnormal supply voltage,

earphone socket defective, C38 (1000MFd), TR9 (AC187), C36 (250MFd), C33 (1000MFd), TR10

(AC188), R33 (27W ), R32 (68W ), R30 (39W ), R31 (180W ), D1 (CD2A), TR7 (BC148B), C50 (330Pf),

C29 (1MFd), R29 (100W ), R26 (2K7), R25 (680K), TR5 (BC148B), R27 (12W ), C26 (1KPf), C25

(1MFd), C51 (0.1MFd), C24 (1000MFd), RV3 (10K), R21 (2K2), C15 (5MFd) short, TR2 (BC148)

& its related components, C11 (1000MFd), R19 (680W

), R8 (15K), R16 (2K7), R17 (1K2), C12(600Pf), C16 (47MFd), R12 (100K), R9 (100W ), TR1 (BC148B) & its related parts, C9 (5MFd), dry


Fault Due to Mechanism :

R/P head misadjusted, pinch roller defective, capstan rod, flywheel, bush, clutch wheel, motor

pulley, motor, speaker paper cone.


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Play-Back is OK but no Recording :

Recording switch point open at record mode position, R47 (12W ), TR11 (BC148B), R46 (39K),

C45 (0.022MFd), C44 (0.047MFd), L15, L16, C42 (4700Pf), C41 (300Pf), RV5(47K), C43 (1KPf),

R4 (10K), C4 (200Pf), R7 (15K), R53 (10W ), R/P head faulty, mic socket or condenser mic faulty, dry


Disturbance in Recording :

Loose contact in recording switch, D2 (OA79), R34 (680W ), C32 (470MFd), TR6 (BC148B),

C23 (47MFd), R13 (5K6), C14 (3K3Pf), TR11 (BC148B) & its related components, L16, L15, C42

(4700Pf), erase head defective, C41 (300Pf), loose contact, dry solder, check print.

Humming Sound :

Recording switch loose, D8-D11 (IN4001 x 4), C46 (640MFd), C38 (1000MFd), D7, TR12

(BC148B), dry solder, check print.

Tape Function is OK but No Sound of Radio Band :

TAPE/RADIO selector switch, R45 (100W ), C40 (220MFd), R44 (1K5), R22, R35 (100W ),

R24 (33K), R28 (18K), R15 (18K), R10 (100W ), R11 (10W ), R20 (680W ), IFT-1, IFT-2, IFT-3, D3

(OA79), C18, C28, C30 (0.047MFd), C22 (2MFd) short TR3 (BF194) & its related components, TR4

(BF195C) & related parts, TR8 (BF195D) & related parts, loose contact or dry solder, check print.

Low Sound of Radio Band :

IFT weak or misaligned, R44 (1K5), R24 (33K), R28 (33K/18K), C22 (2MFd), C28 (0.047MFd),C19 (3600Pf), TR4 (BF195C) & its related components, D3 (OA79) TR8 (BF 195D) & related

components, loose contact or dyr solder, check print.

SW Band is OK but MW Band is not working :

Bans switch point open at MW band position, C5 (365Pf), C3 (0.01MFd), R6 (4.7W ) open, C1

(12Pf), C8 (15Pf), trimmer CT2-CT3 (15Pf) short, MW oscillator, MW antenna coil open, moisture

on MW oscillator coil, loose contact or dry solder, check print.

MW Band is OK but SW Band is not working :

Band switch point open at SW band position, C6 (3000Pf), C7 (3300Pf) open, trimmer CT1

(10Pf), CT4 (15Pf) short, SW oscillator, SW antenna coil open, loose contact or dry solder, check

print.

Disturbed and Booming Sound of Radio Band :

Gang capacitor CV1-CV2 (335Pf) loose, trimmer loose, band switch loose, oscillator coil or

IFT instable, C19 (3600Pf), C27, C31 (200Pf), C22 (2MFd), C18, C28, C30 (0.047MFd), C40

(220MFd), RV1 (1K), loose contact or dry solder, check print.


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Result : Tape recorder and Two-in-one kits fault finding procedure is studied.

18. RECTIFY THE FAULTS IN AUDIO CD PLAYER

Aim : To rectify the faults in Audio CD Player

Equipment needed : Audio CD player, servicing tools kit and multimeter.

Theory :

1) Vision comes but disc tray does not open or pressing open / close button on front panel or on remote.

2) Methods of testing further IF, Cd remains loaded in deck but play does not takes place.

Results : Faults in Audio VCD are studied.


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Max Marks : 50

Periods : 5 periods per week Total periods : 160

II Year PRACTICAL - I

1. Study of servicing tools and instruments (Soldering Iron, Screw Driver Set,

Tweezer, Nose Plier, Cutter, Hammer, File, Desolder Pump, Squeezer). - 10

2. Electronics lab safety precautions (Regarding Wiring, Flooring,

First Aid Treatment). - 10

3. Soldering Practice on PCB and Wiring Practice - 10

4. Familiazation and Testing of Electronic components like resistor, capacitor,

inductor, transformer, loud speaker, semi conductoring devices like diode,

Transistor, IC Packages - 10

5. Study of power supply stage in Radio Receiver

(Full wave bridge Rectifier with filter) - 10

6. Study of RF output stage, voltage measurements - 10

7. Study of dectector and AF Voltage Amplifier, Voltage measurement - 10

8. Study of IF Amplifier stage and Voltage measurement - 10

9. Study RF Amplifier, Mixer, Local oscillator stage and voltage measurement - 1010. Study of FM Receiver - 10

11. Study of IC version 2-band Radio AF/FM Radio Receiver - 10

12. Study of Multiband Radio Receiver - 10

13. Mension typical faults in a Radio Receiver and observe the effect on Voltage

data and performance of the Radio Receiver - 10

14. Study of Public Amplifier system and measurement of standard voltages

at various points - 10

15. Rectify the faults in PA system - 05

16. Study Tape Recorder, Two-in-one and Audio CD Player - 05

17. Rectify the faults in the Tape Recorder, Two-in-one - 05

Communication Engineering Laboratory - I

communication engg lab

Documents