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COMMUNICATIONENGINEERING

LAB - IMANUAL

STATE INSTITUTE OF VOCATIONAL EDUCATIONDIRECTOR OF INTERMEDIATE EDUCATION

GOVT. OF ANDHRA PRADESH

Telugu Academy Publication : Vocational Course - fyctec

INTERMEDIATEVOCATIONAL COURSE

SECOND YEAR

COMMUNICATION ENGINEERING LAB - IMANUAL

FOR THE COURSE OFELECTRONICS

ENGINEERING TECHNICIAN

STATE INSTITUTE OF VOCATIONAL EDUCATIONDIRECTOR OF INTERMEDIATE EDUCATION

GOVT. OF ANDHRA PRADESH

2005

Intermediate Vocatioinal Course, 2nd YearCOMMUNICATION ENGINEER LAB - I

MANUAL(For the Course of Electronics Engineering Technician)

Author : Sri. M. Shanmukha CharyJ.L in Electronics,

Govt. Jr. College, Malkajgiri, Secundrabad.

Complied by : Sri. M. Shanmukha CharyJ.L in Electronics,

Govt. Jr. College, Malkajgiri, Secundrabad.

Price : Rs. /-

Printed in IndiaLaser Typeset Reformatted by SINDOOR GRAPHICS, Dilsukhnagar, Hyderabad-60.

Phone : 24047464

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

1Communication Engineering Lab - I

AIM :

Study of servicing tools and instruments, Soldering Iron, Screw Driver Set, Tweezer, NosePlier, 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 calledsolder applied in the molter state.

Soldering Iron, consists of insulating handle, connected through a metal shank to the bit. Thebit is made of Iron has got good heat capacity and has good thermal conductivity. Generally someirons have thermostatic central to keep the temperature of the bit constant wattages 15W, 25W, 50Wand 100 Watts.

The low wattage iron like 5W, 5W are used to assemble components like FET’s or MOSFET’s

For audio/video circuits 15W, 25W.

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

SOLDERING IRONFig 1.1

SOLDERING GUNFig 1.2

1. SERVICING TOOLS AND INSTRUMENTS

Insulated feed handle

Filament

Bit

Metal Shank with bit

Soldering TipBody

Main Chord

2

Solder Squeezer :

It is mainly used to suck the molter solder completely at the joints to be desolder in order toensure, effective desolder, it consists of a spring placed in a hollow tube with a mechanism to apply orrelease force on the spring. Initially the spring is compressed by applying force. When the force of thespring is released using press release button the spring produces a sucking force through a nozzlewhile retaining its original shape. This sucking force can be used to remove the molten solder at thetime of desoldering.

Soldering Gun :

Soldering gun is a soldering tool used for soldering at a given instant heat. High current flowsas 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 pointof 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 ofpromoting 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 assemblingdiscrete 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 DRIVERFig 1.3

Blade or HandleShank

Tip


Common Screw Driver :

It is used to meet different types of jobs where plenty of room is available and the head of thescrew is out in the open.

THIN Blade Screw Driver :

It is used for screwing or unscrewing thescrews 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, grippingoperation by hand, holding jobs, twisting wiresand a number of other operations in electricalwiring.

Nose Plier :

As the name implies with a thin nose,these are used for bending, holding thin wiresand forming eyes of the wires.

Ball Peen Hammer :

It consists of hammer face, which is usedto drive in, nails in to wooden bottom or for gen-eral work and end for cutting wall plaster andbricks when it is necessary to take wiring fromone room to another.

INSULATED PLIERFig 1.6

Insulated HandlePivot

Wire CutterJaw

THIN BLADE SCREW DRIVERFig 1.4

HEAVY-DUTY OR SQUAREBLADE SCREW DRIVER

Fig 1.5

LONG NOSE PLIERFig 1.7

BALL - PEEN HAMMERFig 1.8

Ball - Peen

CheekEyePost

FaceHead

Handle

4

Claw Hammer :

It is used for duel - purpose hammer. Ithas one side hammer face, which is used to drivein nailsor general purpose and claw at other endfor pulling out nails.

Hacksaw :

It is especially designed fool for cuttingmetals like conductors, cables etc.,

Wooden Saw or Tension Saw :

It is used for cutting small jobs likecutting wooden batten, wooden black boards etc.,

Wooden Chisel :

It is used for cutting un wasted woodenpieces of the wooden boards.

COLD Chisels :

It is used for plaster cutting or far brick cutting.

BALL - PEEN HAMMERFig 1.8

HandleCheek

Face

Claw

Eye

HACK SAWFig 1.9

Frame

Wing NutHandle

Pin

WOODEN CHISELFig 1.10

Heel ToothToe

BackBladeHandle

Blade

CuttingEdge

FerruleTangHandle

WOODEN CHISELFig 1.11

COLD CHISELSFig 1.12


Hand Drill machine :

It is used for making holes in woodenbatter, Wooden blocks, Wooden boards etc., tofacilitate the passage of insulated wires.

Scratch awl :

It is very sharp tool, it should be handledcarefully. It is used or making small hole orimpression is made into the wooden beforescrewing

Rawl Plug Jumper :

It is used to make holes in stone walls orconcrete walls and should not be used onmetals.

Centre Punch :

It is used for mark the location of holesto be drilled.

Electrician Knife :

It is used for removing the insulation from the wires.

Files :

Files are used to remove the waste andrough or burrs on wires and joints etc.,

HAND DRILLFig 1.13

Drive Wheel

Main Handle

Jaw

Drill

SideHandle

Chuck Pinion

SCRATCH AWLFig 1.14

Sharp PointHandle

RAWL PLUG JUMPERFig 1.15

Rawl Plug Bit

CENTER PUCHFig 1.16

ELECTRICAL KNIFEFig 1.17

Trip

ELECTRICAL KNIFEFig 1.18

Face

Length

HeelHandle

TangEdge

6

Try Square :

It is used for making and checking the angles of 90

Pipe Vise :

It is used for holding the conduits duringconduit cutting or cutting threads or for bendingconduits.

Taps :

It is used for cut internal threads for conduits.

Results : All servicing tools and instruments are studied carefully.

Questions :

1) Name the servicing tools2) Name the servicing instruments.

T - HANDLE - TAP WRENCHFig 1.19


Intelligent and prompt action of First - Aid is required in case of electric shock. If the firstaider is not cautions, if any one receive electric shock or even die along with th ecasuality. Everyemployee/worker in the electrical field or those who are having electric supply should make themselves familier with instenctions in the labaratory.

Removal of Cantact :

When a person gets a shok and still he/she is in cantact with the supply/conductor first switchoff the main supply. It the switch or main is not found cut the cable with the help of axe or plastichandled knife but dont use scissor. It insulated material which is dry, if available rubber gloves shouldbe worn, if not dry coat, cap, clothing or folded newspaper should be used while removing the casualityviction. In the case of HT supply, it is most dangerous. The casually may not be actual cantact with thewire as the current can pass through the gap causing an arc. The first - aid kit should keep away fromthe wires and the casually should be dragged out by means of a walking stick, dry rope, dry bomboostick etc.,

See the victims cloths and extinguish the spark’s if check the victim if he/she is breathing but uncon-scious call for a doctor. If the victim is not breathing, immeadiatly start artificial respiration as de-tailed below until first aid arrives or a doctor.

Fig 2.1

Victim has burn’s on back side :

Lay the victim / patient as shown in fig (a) knel over the patient and place both the hands on thethin portion near the lowest rib in such a fashion that both thumbs almost touch each other and thegingers spreads. Now press gently by leaning forward for about 2 to 3 seconds as shown in fig (b).Now release the pressure slowly and come back to original kneeling position for about 2 to 3 secondsas shown in fig (a). Repeat these two movements for about 10 to 15 times in a minute until doctorarrives. This process initialises the breathing by expansion and contraction of patient lungs. Thismethod is also known as schefer’s method.

Fig 2.2

2. ELECTRONIC LAB SAFETY PRECAUTIONS

8

Victim has burns on front side :

Lay the patient as shown in fig. (a), loosen the clothes around the chest and stomache, thenplace 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 arehorizontal, keep them in that position for about two to three second as shown fig. (a). Next bring thepatient 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 shouldnot be stopped until the doctor arrives. This method is also known as silvster’s 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.


Aim :

Soldering practice on PCB and wiring practice.

Equipment required :

PCB’s 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 oneside 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 mountedelectronic components like resistors, capacitors, coils, transformers, tubes, transistors, diodes, IC’s.Suitable holes are punched in the PCB for mounting the components which are connected to theconducting 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 thoseusing semiconductor devices like transistors and IC’s. Use of PCB’s makes the circuit assembly alsolends itself efficiently to mass production method.

3. SOLDERING PRACTICE ON PCB AND WIRING PRACTICE

+VCC

VO

RE

Cb

RECE

CCRCR1

R2

CER2

CC

R2

TR1

250 mF

220 mF 220 mF470 W

3.3 K

33 KRC 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


Q

CT1

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 signalis in the audio frequency range 20Hz to 20KHz. In any communication system we can hear the speach300Hz - 3400Hz range called voice frequency. The amplifier which is operated in the above range iscalled 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 shortbelow of leaky check base and

ground voltage2. Hum Transistor terminals are Use shielded

not properly shielded.3. Intermittent Coupling capacitor may Replace capacitor and

Output open intermittenly volume check volume controlcontrol defective

4. No Output All voltages across the Check power supplytrnasistor leads are dead.

PUSH PULL AMPLIFIERFig 6.1

6. STUDY OF OUTPUT STAGE, VOLTAGE MEASUREMENT

24

Noise :

If voice coil rubs the body of the speaker cracking noise will be produced, may be core paperbroken 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 onvoltage 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 zerovoltages.

Open emitter resister :

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

Coupling Capacitor :

If the coupling capacitor open results the receiver is in dead mode. If it is leaky the output isdistorted. If it is short the produces excessive distortion.

Volume Control / Tone Control :

Noisy volume or tone control is to be replaced


Table :

S.No. Voltage on transistors collector output Voltage on RL Speaker AFT1 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.

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. Thediode has same propecties as detection and rectification.

The diode is used for AM detection / demadulation. In the given circuit, C is a small capacitenceand R is a large resistance. The parallel combination of R,C with load resistance across RL the outputvoltage 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 ofripple. 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 couplingcapacitor C11(8PF), Resistors R12, R13 are the voltage dividers for the base emitter bias. ResistorR14 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 decouplingsignals from all stages.

DETECTORFig 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 dualtrace CRO.

7. STUDY OF DETECTOR AND AF VOLTAGE AMPLIFIERMEASUREMENT OF VOLTAGES

IFT2

R

R

R

Q OA79

CAVC

Q IFT3

To AF Amplifier

C


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 TransformerOA79 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

30

Aim :

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


A radio receiver, AC voltmeter and connecting wires.

Theory :

RF AMPLIFIERFig 9.1

RF Stage :

The desired RF signal selected by the tuned antena circuits is applied to the input of the radiofrequency amplifier. After amplification from the RF stage, the modulated RF signal passed on to thenext 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 themixer. 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 tothe 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, themodulated IF signal at the collector which applies it to the IF transformer. Capacitor C2 (0.02mF) is

9. RF AMPLIFIER, MIXER, LOCAL OSCILLATOR

AntennaConverter

R1

C1

R2

R3

L1C3

C2C4 C5

C6

_ +Battery


an IF decoupling capacitor to prevent IF signals from being fed back to the base. Taps are used tooscillator coil and the IF transformer coinding for impedance matching Q1 is PNP transistor in whichthe 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 outputVBE VCE voltage

Result :

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

Questions

1. Write RF voltages2. Write testing processor of RF amplifier, local oscillator and mixer stages

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 75KHzaround the carrier frequency. Propagation at VHF is restricted to line of sight and coverage is usuallyonly for a radius of 50KM around the transmitter location. The programmes broad cast on thesechannels in the past have been mostly music and the basic modulating frequency band width is 15KHzas opposed to the 5KHz used on AM stations.

10. STUDY OF FM RECEIVER

FM RADIO RECEIVERFig 10.1


Figure shows the block diagram of a typical FM broadcast receiver. It is a supernetero dyrecircuit with a tuned RF amplifier so that maximum signal sansitivity is 1 to 10mV. The RF stage tunedcircuits and local oscillator are tuned by a three ganged variable capacitor controlled from a panelknob. The oscillator frequency can be varied from 98.7 MHz to 118.7 MHz. Yielding an intermediatefrequency 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 sunedto give the desired band pass characteristics this is centered on 10.7 MHz and has a 180 KHz bandwidth to pass the desired signal. Amplitude limiting is usually arranged to have an on set throshold ofabout 1mV at the limiting - stage input, corresponding to the level of input signal. Which may be setat 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 frequencyprogramme comes from the loud speaker.

Result :

FM Radio receiver studied.

Questions

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

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 75KHzaround the carrier frequency. Propagation at VHF is restricted to line of sight and coverage is usuallyonly for a radius of 50KM around the transmitter location. The programmes broad cast on thesechannels in the past have been mostly music and the basic modulating frequency band width is 15KHzas opposed to the 5KHz used on AM stations.

10. STUDY OF FM RECEIVER

FM RADIO RECEIVERFig 10.1


Figure shows the block diagram of a typical FM broadcast receiver. It is a supernetero dyrecircuit with a tuned RF amplifier so that maximum signal sansitivity is 1 to 10mV. The RF stage tunedcircuits and local oscillator are tuned by a three ganged variable capacitor controlled from a panelknob. The oscillator frequency can be varied from 98.7 MHz to 118.7 MHz. Yielding an intermediatefrequency 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 sunedto give the desired band pass characteristics this is centered on 10.7 MHz and has a 180 KHz bandwidth to pass the desired signal. Amplitude limiting is usually arranged to have an on set throshold ofabout 1mV at the limiting - stage input, corresponding to the level of input signal. Which may be setat 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 frequencyprogramme comes from the loud speaker.

Result :

FM Radio receiver studied.

Questions

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

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 InAM receiver again there are two bands i.e. mediumwave and shortwave. The shortwave frequencyrange 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 switchopen, 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 switchopen, C72 (47MF), C71 (220MF) VR2 (10K), C67 (1MF/50V), C69 (47MF), C48 (0.001 MF), loosecontact 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 weakor 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 switchfaulty, dry solder, check print.

11. STUDY OF IC VERSION 2-BAND AM/FMRADIO RECEIVER AND TAPE RECORDER


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 papercore.

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 papercore 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, checkprint.

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, loosecontact or dry solder, check print.

Disterbence in Recording :

C62 (0.068mF), C57 (100mF/63V) D1 (MA150) open or short, Q1 (2SC1684) and its relatedcomponents, 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 pinchroller, 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 defectiveD2 (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, S1band switch defective, loose cantact, dry solder check point.

36

AM-FM RADIO TAPE RECORDERFig 11.1


FM Band not working :

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

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 sameas in the case of superneterodyre receiver. The frequency band or the wave band covered is decide bythe 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 itbecomes neccessary to have a shortwave bands in addition to the mediumwave (MW), so that stationsbroadcosting 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 secondband of frequencies. For a second band of frequencies, a different number of a tunes is required bothfor antenna section and the oscillator section of the converter stage. The variable capacitors, which areparts of a two gang capacitor will remain the same. Thus for changing one wave band to another, oneset of coils and trimmers should be connected to the circuit, simultaneously in the antenna section andthe oscillator section of the converter stage of the receiver. This involves a number of switchingoperations that must be performed before a waveband can be changed. This is done with the help of aspecial multicantact switch known as the band change switch or a wave change switch. The commonmost 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 suitableinsulating material. A smaller circular plate of the same insulating material carrier two semicircularmetalic strips with projections on one end, which will make contact positions MS, SW1, SW2 one byone 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


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

40

Aim :

Mension the faults in Radio Receiver and observe the effects on voltage data and performenceof 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 Band2. Shortwave working but MW is not working3. 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 contactposition should be adjusted to switch position, MW oscillator, MW antenna coil open, moisture onMW 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 switchloose, 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, beltis tight rectifing and filter circuit components failure, weak motor, loose cantact, dry solder, checkprint, 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 ordry solder, check print of PCB.

13. FAULTS IN RADIO RECEIVER


BLOCK DIAGRAM OF FM RADIO RECEIVERFig 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

RFtunedamp

Gangcapacitor

Auido10.7 MHz with 180 KHz

bandpass

88-108MHz

speaker

Audioamplifier

Varactortrimmer

Volumeand tonecontrol

AFCDelayedAGC

detector

Localoscillator

Deemphasis

Antenna

Discriminator

IFtuned

limitingamp

IFtunedamp

Mixer

98.7 - 118.7MHz

42

Aim :

Study of Public Address System, Microphone, Amplifier and loud speakers and interconnections.

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 bylarge number of people gathered and at a considerable distance.

A basic public address system has input source is a microphone, which pick ups low levelsound 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 improvesthe signal gain. The gain depends upon the number amplifiers are used in casteded stages. Thisdetermines the AF power levels. This amplifier consists of 3 or 4 microphone auxillary circuit at inputlevel with controlling switches for each microphone. Each microphone has got volume controllers tocontrol audio signal levels.

Special electronic circuit provides and excellent sound quality. Cut and Boost type Bass andTreble 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 theoutput 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 MonanealTape speed : 4.75 Cm/SecFF/Revind Time : 190 seconds with C.60 tapeTape speed accuracy : within +2% - 1%Wow and flutter : 0.35% Nominal

14. PUBLIC ADDRESS AMPLIFIER


Amplifier section :

Output power : 100W (RMS) max75W RMS at 10% THD70W RMS at 5% THD (Rated)

Frequency response : 55Hz - 15000 Hz 3dBS/N Ratio : > 55dBInput channels : 4 X Mic 0.6 mV (Lo - Z) 4.7 K

1 X Aux 100mV / 470 KSpeaker outputs : 4,8,16 and 100WLine output : 1000mV / 3.5 KTone controls : Bass - 10dB + 7 dB at 100Hz

Treble - 10dB + 7 dB at 10KHz

GENERAL

Power supply mains : 220 - 240V Ac 50/60 Hz140 VA at rated output

Battery : 12 - 14V dc, Drains 5A/12VSemiconductors : 17 Transistors, 11 Diodes, 2 Zener diode

6 LED’s 2ICProtections : Ac fuse (2Amps, 240V)

DC fuse (10Amps)Indicators : Pilot LED

5 LED Array for output levelDimensions Net Weight : L 385 x D310 x H130 mmNet Weight : 9.6 Kg.

Microphone Connection :

4 independent microphone inputs have been provided through jacks on the front panel. Mic 4input may be used by keeping the Mic / Tape - Lo Tape Hi selector switch at MIC position.

Microphone inputs are unbalanced Low impedence usable with microphones of inpedence200 - 600. In case microphones with both HIGH and LOW impedence are used, be some that switchon the microphone is at low position.

Microphone with upto 30 meter long cable can be used always use good quality shielded cables.

For good intelligibility of sound, the microphone should be placed atleast 20 Cms away fromthe speakers mouth. Keeping the microphone too close to the mouth will result in distortion of soundand may even cause damage to the diaphragm of the microphone.

44

MICRO PHONE - SPECIFICATIONSFig 14.2


SPEAKER CONNECTIONS :

Speaker impedence taps of 4, 8 and 16 have been provided for direct connection of speakers to theamplifier when the distance between the amplifier and speakers is less than 50 meters. Use 23/26 orthicker cable for connections. Be sure that the total impedence of the speakers is equal to or more thanthe 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 samedirection, it is essential that their cones / diaphragms move in unison. Otherwise, the sound output ofone speaker will cancel the sound output of other. To avoid any mistake, the terminals of all driverunits are marked L1 & L2. For correct wiring refer the sketches.

PAS CONNECTIONSFig 14.4

BAD

GOOD

GOOD

GOOD

GOOD

BADGOOD

GOOD

GOODGOODGOOD

BAD

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

46

WARNING :

Connect a set of speakers to EITHER any ONE of the low impedence taps 4 & 8 or 16 or to100V line output. Do not use more than one speaker output connection at a time.

AMPLIFIER CONNECTIONSFig 14.5

Result :

PAS is assembled in college ground observed sound distribution throught the ground in publicmeeting.

Questions

1. Study the block wise operation and specification of public address system2) Methods of testing further IF, Cd remains loaded in deck but play does not takes place.


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 bylarge 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 connectingloud 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 beequal to the output impedance of the amplifier. If the speaker are connected in parallel R = see theimpedence offer by the output terminals of this amplifier.

Impedence Matching :

To transfer maximum power from amplifier to loud speaker the output impedence of th eamplifieris 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 tocable 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 withLMT.

15. RECTIFY THE FAULTS IN PUBLIC ADDRESS AMPLIFIER SYSTEM

48

SPEAKER INTER CONNECTIONSFig 15.1


AMPLIFIER CIRCUIT IC VERSIONFig 15.2

50

LMT’s are used in a large installation which require a large number of speakers to beconnected at a distance. As the length of the cable increases so the strength of the sound signaldecreases. Hence in installations where the length of the cable is sub stantial. LMT’s are used. Whenusing LMT’s 100V, line is used. This 100V line system comparable to the electricity distributionsystem. In electricity distribution system a large voltage is transmitted from the sub-station such highvoltage 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. isfed to LMT’s These LMT’s act as step down transformers. As the electricity wiring system in housesis 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 / Hornspeakers 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 theelectrical earth / any water pipe.

Result :

Faults in PAS is studied.

Questions

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


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 orspeech

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 taperecorder 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 theamplifier to the microphone and the output is connected to the record head so that the amplified audiosignals are impressed on the moving tape. In the playback position, the magnetic signals picked up ordetected from the tape by the same head are applied to the input of the amplifier for reporduction bythe loudspeaker. One and the same head performing the combined functions of recording and playbackis known as the record playback head. The tape is wound on the supply reel and is moved at constantspeed and under constant tension in front of the record / playback head during recording and playbackoperations. 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 fromthe tape before the tape reaches the record head for a fresh recording. The erase head is energised bythe HF oscillator which also applies an AC bias to the record head during the recording process forimproving the quality of recording. The erase h ead is not energised ruing the playback process toprevent the recorded matter from being erased. A tape transport system consisting of a motor, driveassembly, belts and pulleys enables the tape to move at constant speed during record and playbackprocess and also to move faster during the fast-forward and rewind processes.

TAPE TRANSPORT MECHANISMFig 16.1

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

Takeup Real

Drive Belt

TapePinch Roller

Capstan

Fly Wheel

Motor andFan

IdlerDriveSupply Reel

Bus Idler

Brake Shoe

Tape Guide

Erase HeadRecord /Playback Head

Pressure Pad

RubberisedIdler Wheel

52

TAPE CIRCUITFig 16.2


1. ON/OFF switch2. Volume control3. Play press button4. Rewinding5. Fast Forward button6. Recording7. Eject / Stop8. Pause.

All above are called operating controls of a tape recorder. The tape transport mechanism andmotor 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 beenreplaced by trannsistors. With the use of transistors, the size and weight of all other componentsrequired 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 transistorreceivers are of the superheterodyne type. A transistor superheterodyne receiver makes use of thestages which function in the same way as the stages of a valve type receiver. However, there arecertain 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 astandard transistor receiver.

54

TWO IN ONERadio Cassette Recorder

Fig 16.3

CD Player :

A recorded compact disc (CD) is played in a CD/VCD player, detection of pits and present onthe CD is also done by a laser beam of low power are focused on the rotating CD. If the rays reach aflat they will come back after reflection from the flat, but if fail on the PIT then they will get absorbedthere 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 tothose signals which were given at the input of the video card. By giving audio signals to the loudspeaker 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 outerdiameter of 120mm. The aluminium coating present on the CD is 116mm diameter inner diameter of50mm, a CD consists of a hole with diameter is 15mm. The recording is done on thousands of spiraltracks present on this 33mm wide ring. The CD thickness about 1.2mm. on CD can store 800MB ofaudio/video programme. With a duration of 1 hour.


CD PLAYER FUNCTIONAL DIAGRAMFig 16.4

METHOD OF TEST-ING LENS UNIT

DIRECTION OFMOVEMENT OFLENS DURINGTESTING

56

2. Thousands of tracks are present on the 33mm wide ring. A gap is maintained between two nearlytracks on these tracks of a laser beem is focused.

3. A high power laser (Light Amplification by stimulated emission of radiation) used during CDwriting. 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 theouter 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 one2. Study the Two-in-one. Write working3. Study the CD Player. Write working

CDFig 16.5


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 drysolder, 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 RECORDERAND TWO-IN-ONE

58

RADIO TAPRE RECORDER IC VERSIONFig 17.1


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 istight, 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 (Rightor Left) :

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

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.

60

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 drysolder, check print.

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 relatedcomponents, 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 orhard 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), drysolder, check print.

Fault Due to Mechanism :

R/P head misadjusted, pinch roller defective, capstan rod, flywheel, bush, clutch wheel, motorpulley, motor, speaker paper cone.


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, drysolder, check print.

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) & relatedcomponents, 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, moistureon 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, checkprint.

Disturbed and Booming Sound of Radio Band :

Gang capacitor CV1-CV2 (335Pf) loose, trimmer loose, band switch loose, oscillator coil orIFT instable, C19 (3600Pf), C27, C31 (200Pf), C22 (2MFd), C18, C28, C30 (0.047MFd), C40(220MFd), RV1 (1K), loose contact or dry solder, check print.

62

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.

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 - 10

10. 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

18. Rectify the faults in audio CD Player - 05

Total - 160

Communication Engineering Laboratory - I

ivc - bie.telangana.gov.inbie.telangana.gov.in/files/communicationengglab.pdf · pliers : these are...

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