Communication Engg Lab

I VC SECOND SECO ND YEA R

n a i c i n h c e T g n i r e e n i g n E s c i n o r t c e l E

COMMUNICATION ENGINEERING LAB - I MANUAL

STATE INSTITUTE INSTITUTE OF VOCA VOCATION TIONAL AL EDUCATION DIRECTOR OF INTERMEDIATE EDUCATION GOVT. OF ANDHRA PRADESH

Telugu Academy Publication : Vocational Course - fyctec

INTERMEDIATE VOCATIONAL COURSE SECOND YEAR

COMMUNICATION ENGINEERING LAB - I MANUAL

FOR THE COURSE OF ELECTRONICS ENGINEERING TECHNICIAN

STATE INSTITUTE OF VOCATIONAL EDUCATION DIRECTOR OF INTERMEDIATE EDUCATION GOVT. OF ANDHRA PRADESH

2005

Intermediate Vocatioinal Course, 2nd Year COMMUNICATION COMMUNICA TION ENGINEER ENGINEE R LAB - I MANUAL (For the Course of Electronics Engineering Technician)

Author : Sri. M. Shanmukha Chary J.L in Electronics, Govt. Jr. Jr. College, Malkajgiri, Secundrabad.

Complied by : Sri. M. Shanmukha Chary J.L in Electronics, Govt. Jr. Jr. College, Malkajgiri, Secundrabad.

Price : Rs.

/-

Printed in India Laser Typeset Reformatted by

D ilsukhnagar,, Hyderabad-60. SINDOOR GRAPHICS, Dilsukhnagar 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 10

4.

FAMILARISATION OF ELECTRONIC COMPONENTS

11 - 20

5.

STUDY OF POWER SUPPLY STAGE IN RADIO RECEIVER

21 - 22 22

6.

STUDY OF OUTPUT STAGE, VOLTAGE MEASUREMENT

23 - 25 25

7.

STUDY OF DETECTOR AND AF VOLTAGE AMPLIFIER

26 - 27 27

MEASUREMENT MEASUR EMENT OF VOL VO LTAGES 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 RECE IVER AND TAPE 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 REC RECO ORD RDE ER TWO TWO-I -IN N-O -ON NE AND AU AUD DIO CD PLAYE YER R

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

Communication Engineering Lab - I

1

1. SERVICING TOOLS AND INSTRUMENTS 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 watta ge iron like 5W, 5W are used to assemble assembl e components like FET’s or MOSFET’s MOSFET’s For audio/video circuits 15W, 25W. For soldering electrical wires 60W, 100W cables which needs a high amount of power dissipation. Insulated feed handle Filament

Bit Metal Shank with bit

SOLDERING IRON Fig 1.1 Body Soldering Tip

Main Chord

SOLDERING GUN Fig 1.2

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 construction. 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, helically 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 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 position. Its size usually various from 4mm to 600mm. B l ade or Shank

Handle

Tip

STANDARD SCREW DRIVER Fig 1.3


3

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 unscrewi ng the screws of switches, lamp holders etc.,

THIN BLADE SCREW DRIVER Fig 1.4

Heavy Duty Screw Driver :

It is used for screwing or Loosening heavy screws. Pliers :

HEAVY-DUTY OR SQUARE BLADE SCREW DRIVER Fig 1.5

These are used for holding or griping small screws or bolts in position, cutting, twisting and bending the wires. Wire Cutter

Insulated Cutting Plier :

Insulated Handle

Jaw Pivot

It is used for cutting wires, gripping operation by hand, holding jobs, twisting wires and a number of other operations in electrical wiring. INSULATED PLIER Fig 1.6 Nose Plier :

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

LONG NOSE PLIER Fig 1.7

Ball Peen Hammer :

Ball - Peen Handle

It consists of hammer face, which is used to drive in, nails in to wooden bottom bott om or for general work and end for cutting wall plaster and bricks when it is necessary to take wiring from one room to another.

Cheek Eye Post Head Face

BALL - PEEN HAMMER Fig 1.8

4

Claw Hammer :

Claw

Cheek Handle

It is used for duel - purpose hammer. hammer. It has one side hammer face, which is used to drive dri ve in nailsor general purpose and claw at other end for pulling out nails.

Eye

Face

BALL - PEEN HAMMER Fig 1.8 Frame

Hacksaw : Pin

It is especially designed fool for cutting metals like conductors, cables etc., Handle

Wing Nut

HACK SAW Fig 1.9

Handle

Blade Back

Wooden Saw or Tension Saw :

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

Toe Heel

Tooth

WOODEN CHISEL Fig 1.10

Wooden Chisel :

Handle

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

Tang

Ferrule

Blade

WOODEN CHISEL Fig 1.11

COLD Chisels :

It is used for plaster cutting or far brick cutting. COLD CHISELS Fig 1.12

Cutting Edge


5

Hand Drill machine :

It is used for making holes in wooden batter, Wooden blocks, Wooden boards etc., to Side Handle facilitate the passage of insulated wires.

Main Handle

Jaw Drive Wheel Chuck Drill

Pinion

HAND DRILL Fig 1.13

Scratch awl :

Handle Sharp Point

It is very sharp tool, it should be handled carefully.. It is used or making carefully making small hole or impression is made into the wooden before screwing

SCRATCH AWL Fig 1.14

Rawl Plug Jumper :

It is used to make holes in stone walls or concrete walls and should not be used on metals.

Rawl Plug

Bit

RAWL PLUG JUMPER Fig 1.15

Centre Punch :

It is used for mark the location of holes to be drilled.

CENTER PUCH Fig 1.16

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.,

ELECTRICAL KNIFE Fig 1.17 Tang

Length

Edge Trip

Handle

Heel

Face

ELECTRICAL KNIFE Fig 1.18

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 thread s or for bending conduits. Taps :

T - HANDLE - TAP WRENCH Fig 1.19

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.


7

2. ELECTRONIC LAB SAFETY PRECAUTIONS Intelligent and prompt action of First - Aid is required in case of electric shock. If the first aider is not cautions, if any one receive electric shock or even die along with th ecasuality. ecasuality. Every employee/worker in the electrical field or those who are having electric supply should make them selves 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 switch off the main supply. supply. It the switch or main is not found cut the cable with the help of axe or plastic handled knife but dont use scissor. scissor. It insulated material which is dry, dry, if available rubber gloves should be worn, if not dry coat, cap, clothing or folded newspaper should be used while removing the casuality viction. In the case of HT supply, supply, it is most dangerous. The casually may not be actual cantact with the wire as the current can pass through the gap causing an arc. The first - aid kit should keep away from the wires and the casually should be dragged out by means of a walking stick, dry rope, dry bomboo stick etc., See the victims cloths and extinguish the spark’s if check the victim if he/she is breathing but unconscious call for a doctor. If the victim is not breathing, immeadiatly start artificial respiration as detailed 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 hand s on the thin portion near the lowest rib in such a fashion that both thumbs almost touch each other and the gingers 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 seconds as shown in fig (a). Repeat these two movements for about 10 to 15 times in a minute until doctor arrives. This process initialise initialisess the breathing by expansion and contraction of patient lungs. This method is also known as schefer’s method.

Fig 2.2

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 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.


9

3. SOLDERING PRACTICE ON PCB AND WIRING PRACTICE 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 one side of which a complete layout diagram of an electronic circuit consisting of copper or silver conducting 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, IC’s. 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 and with 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 IC’s. Use of PCB’s PCB’s makes the circuit assembly also lends itself efficiently to mass production method. SINGLE STAGE TRANSISTOR AMPLIFIER +VCC RC 5 K R2 33 K 220 mF

5 mV

S

R2

CC

220 mF BC 145

470 W VO

3.3 K

Fig 3.1

CE 250 mF

RE 1.2 K

PCB LAYOUT

Fig 3.2

COMPONENT PCB LAYOUT R1 Cb

RC

CC

TR1 R2

Fig 3.3 RE CE


23

6. STUDY OF OUTPUT STAGE, VOLTAGE MEASUREMENT Aim :

Study of push pull amplifier and measurement of output voltages Equipment Required :

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. 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 the transistor radio receiver as floows. S.No.

Symptoms

Possible Cause

Remedies

1.

Poor So Sound

Collector Voltage of of tr transistor below

2.

Hum

3.

Intermittent Output

4.

No Output

Transistor terminals are not properly shielded. Coupling capacitor may open intermittenly volume control defective All voltages across the trnasistor leads are dead.

B T1

Compilling ca capacitor sh short of leaky check base and ground voltage Use shielded Replace capacitor and check volume control Check power supply

C Q E

T2 C

R

R

R r B

R

E Q C

C

PUSH PULL AMPLIFIER Fig 6.1

24

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 effect on voltage data. IC get overheated, replacement is only one remeady. remeady. Common Troubles Troubles in the Audio Circuit : Distortion :

This occurs by in proper biasing due to an open resistor. Defective transistor lack of heat measure voltage at th eemitter junction. Low Volume : Open bias resistors or defective transistor. Measure Voltage Voltage / resistances in the stage. Defective 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


25

Table :

S.No.

Voltage on transistors collector T1 T2

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.

output Voltage on R L

Speaker AF voltage

26

7. STUDY OF DETECTOR AND AF VOLTAGE AMPLIFIER MEASUREMENT OF VOLTAGES

Aim :

Study of Detector and AF Voltage Amplifier Measurement of Voltages Equipment Required :

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. demadulation. In the given circuit, C is a small capacitence 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 equal to 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. 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 (0.00 5mF) 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. Q

Q

IFT3

OA79

R To AF Amplifier

IFT2 R R C

AVC

C

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.


27

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 OA79

Demodulated output voltage

AF power transistor voltages VCE VBE

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

AF Transformer secondary voltage

30

9. RF AMPLIFIER, MIXER, LOCAL OSCILLATOR Aim :

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

A radio receiver, AC voltmeter and connecting wires. Theory : Converter Antenna

C4

C1

C5

R3

L1

C2 C3

R2

R1 C6

_ + Battery

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 th e AVc AVc action. acti on. 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 receiver. 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


31

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 VBE

RF output Voltage VCE

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

Mixer output voltage

32

10. STUDY OF FM RECEIVER 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 bas ic modulating frequency band width wid th is 15KHz as opposed to the 5KHz used on AM stations.

FM RADIO RECEIVER Fig 10.1


33

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. 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

32

10. STUDY OF FM RECEIVER 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 bas ic modulating frequency band width wid th is 15KHz as opposed to the 5KHz used on AM stations.

FM RADIO RECEIVER Fig 10.1


33

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. 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

34

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

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) (IN 4002) 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 (470MF/10V)) open C76 (100MF), IC2(mPC1213C) recording switch faulty, dry solder, check print.


35

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), (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), (0.0015mF) , CT3, SW OSC. Coil defective, S1 band switch defective, loose cantact, dry solder check point.

36

AM-FM RADIO TAPE RECORDER Fig 11.1


37

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 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

12. STUDY OF MULTI BAND RADIO RECEIVER 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 sw itches are different remaining stages stage s are same as in the case of superneterodyre receiver. recei ver. 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 antenna 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 bands also 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 the outer fibre plate remain permanently in contact with their respective number of strips.


39

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

13. FAULTS IN RADIO RECEIVER 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 band 4. 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 related 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, curren t, 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.


41

Antenna 88-108 MHz RF tuned amp

Mixer

10.7 MHz with 180 KHz bandpass IF IF tuned tuned limiting amp amp Delayed AGC detector

Gang capacitor

Auido Disc riminator

De emphasis

AFC

Volume and tone control

Local 98.7 - 118.7 oscillator MHz Varactor trimmer

Audio amplifier

speaker

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

42

14. PUBLIC ADDRESS AMPLIFIER 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 playback of 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. quality. Cut and Boost type Bass and Treble controls, master control, 4 input volume controls and a special feature of adjusting tape sensitivity through tape Hi/Lo Hi/ Lo switch have been provided. An LED ARRAY 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 AMPLIFIER Fig 14.1 Specifications Player Section :

Track system Tape speed FF/Revind Time Tape speed accuracy Wow and flutter

: : : : :

2 Track Monaneal 4.75 Cm/Sec 190 seconds with C.60 tape within +2% - 1% 0.35% Nominal


43

Amplifier section : Output power

:

Frequency response S/N Ratio Input channels Speaker outputs Line output Tone controls

100W (RMS) max 75W RMS at 10% THD 70W RMS at 5% THD (Rated) : 55Hz - 15000 Hz 3dB : > 55dB : 4 X Mic 0.6 mV (Lo - Z) 4.7 K 1 X Aux 100mV / 470 K : 4,8,16 and 100W : 1000mV / 3.5 K : Bass - 10dB + 7 dB at 100Hz Treble - 10dB + 7 dB at 10KHz

GENERAL

Power supply mains

:

Battery Semiconductors

: :

Protections

:

Indicators

:

Dimensions Net Weight Net Weight

: :

220 - 240V Ac 50/60 Hz 140 VA at rated output 12 - 14V dc, Drains 5A/12V 17 Transistors, 11 Diodes, 2 Zener diode 6 LED’s 2IC Ac fuse (2Amps, 240V) DC fuse (10Amps) Pilot LED 5 LED Array for output level L 385 x D310 x H130 mm 9.6 Kg.

Microphone Connection :

4 independent microphone inputs have been provided through jacks on the front panel. Mic 4 input 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 inpedence 200 - 600. In case microphones with both HIGH and LOW impedence are used, be some that switch on 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 from the speakers mouth. Keeping the microphone too close to the mouth will result in distortion of sound and may even cause damage to the diaphragm of the microphone.

44

MICRO PHONE - SPECIFICATIONS Fig 14.2


45

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.

SPEAKERS Fig 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. other. To avoid any mistake, the terminals of all driver units are marked L1 & L2. For correct wiring refer the sketches. BAD

GOOD

GOOD

GOOD

GOOD BAD

GOOD GOOD

BAD

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

PAS CONNECTIONS Fig 14.4

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.


47

15. RECTIFY THE FAULTS IN PUBLIC ADDRESS AMPLIFIER SYSTEM 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 connection 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. 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 connect ing 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 outpu t 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 amplifier 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 speakers 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.

48

SPEAKER INTER CONNECTIONS Fig 15.1


AMPLIFIER CIRCUIT IC VERSION Fig 15.2

49

50

LMT’s 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. LMT’s are used. When using LMT’s 100V 100V,, line is used. This 100V line system comparable to the electricity distribution distribut ion 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 supplied to houses is reduced by using a step-down transformer. Similarly a high voltage signal 100V. 100V. is fed to LMT’s LMT’s These LMT’s LMT’s 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 rectificatio rectification n processor


51

16. TAPE RECORDER TWO-IN-ONE AND AUDIO CD PLAYER 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 the record/playback record/playbac k amplifier. 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 recordi ng 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. Bus Idler Supply Reel

Idler Drive Takeup Real

Brake Shoe

Motor and Fan

Tape Guide

Drive Belt

Rubberised Erase Head Idler Wheel Record / Playback Head

Tape Pinch Roller

Pressure Pad

Capstan Fly Wheel

TAPE TRANSPORT MECHANISM Fig 16.1

52

TAPE CIRCUIT Fig 16.2


53

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 / playback mode of operation. Two-in-one :

In this system a radio and tape recorder is separated by a lever switch. In the circuit tape recorder 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 receivers 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 between the properties of transistors and vacuum tubes. In order to bring out clearly the points of difference and similarity between the circuits used in the two types of receivers, the circuit diagram of a standard transistor receiver.

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 information about the combinations combinati ons of PITS and FLATS. FLATS. On these digital signals s ignals thousands of circuits cir cuits 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 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.


55

METHOD OF TESTING LENS UNIT

DIRECTION OF MOVEMENT OF LENS DURING TESTING

CD PLAYER FUNCTIONAL DIAGRAM Fig 16.4

56

CD Fig 16.5

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. Two-in-one. Write working 3. Study the CD Player. Player. Write working


57

17. RECFITY THE FAULTS IN THE TAPE RECORDER AND TWO-IN-ONE 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 Stereo Cassette Recorder Model : C2010 Set Dead, No Play-Back :

Mains lead, transformer T1 (0.7.5V/500mA) (0.7.5V/500mA ) open, D1-D4 (1N4007) open or short, leaf switch not 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 connection 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 (220 W ), 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 (270 W ), C61 (220MFd), C51-C52 (1MFd), VR103-VR203 (50K), R54 (270 W ), C56 (330MFd), C57 (0.1MFd), C11 (100MFd), IC101 & its related parts, dry solder, check point.

58

RADIO TAPRE RECORDER IC VERSION Fig 17.1


59

Distorted Sound : Faults Due to Electronic Circuits :

Speaker paper cone torn or hard or speaker faulty, less or abnormal supply voltage, tone control 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 (270 W ), 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 pul ley,, bush, capstan rod, glinder, gli nder, 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 Volume Level But Distorted Output when Volume 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 tran sformer) 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 (68 W ), 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 (680 W ), R12 (100K), R16 (2K7), R8 (15K), R9 (100 W ), R17 (1K2), C9, C15 (5MFd) open, C10 (2000Pf), (2 000Pf), C11 (1000MFd) short, TR1, TR2 (BC148) open or short, RV3 (10K) open, wire of head connection open, loose contact or dry solder, check print. Low Audio Output :

Less ore abnormal supply voltage, C38 (1000MFd), TR9 (AC187), speaker voice coil short or speaker defective, earphone socket defective, C36 (250MFd), C33 (1000MFd), TR9 (AC187), TR10 (AC188), R33 (27 W ), R32 (6b8 W ), 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 (680 W ), R8 (15K), R16 (2K7), value of R17 (1K2) developed, C16 (47MFd), C12 (600pf), R12 (100K), TR1 (BC148B) & its related components, R9 (100 W ), 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 (27 W ), R32 (68W ), R30 (39W ), R31 (180W ), D1 (CD2A), TR7 (BC148B), C50 (330Pf), C29 (1MFd), R29 (100 W ), R26 (2K7), R25 (680K), TR5 (BC148B), R27 (12 W ), C26 (1KPf), C25 (1MFd), C51 (0.1MFd), C24 (1000MFd), RV3 (10K), R21 (2K2), C15 (5MFd) short, TR2 (BC148) & its related components, C11 (1000MFd), R19 (680 W ), R8 (15K), R16 (2K7), R17 (1K2), C12 (600Pf), C16 (47MFd), R12 (100K), R9 (100 W ), TR1 (BC148B) & its related parts, C9 (5MFd), dry solder, check print. Fault Due to Mechanism :

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


61

Play-Back is OK but no Recording :

Recording switch point open at record mode position, R47 (12 W ), 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 (10 W ), R/P head faulty, mic socket or condenser mic faulty, dry solder, check print. Disturbance in Recording :

Loose contact in recording switch, D2 (OA79), R34 (680 W ), 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 (100 W ), C40 (220MFd), R44 (1K5), R22, R35 (100 W ), R24 (33K), R28 (18K), R15 (18K), R10 (100 W ), 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 (4.7 W ) 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.

62

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

18. RECTIFY THE FAUL AULTS TS IN AUDIO AUD IO CD PLA PLAYER YER Aim : To rectify the faults in Audio CD Player Equipment needed : Audio CD player, servicing tools kit and multimeter. Theory : 1) Vision Vision comes but disc tray does not open ope n or pressing open / close button on front fr ont 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.

Communication Engineering Laboratory - I Max Marks : 50 Periods : 5 periods per week

Total periods : 160

II Year PRACTICAL - I 1.

Study Stu dy of of servi servicin cing g tool toolss and and instr instrum ument entss (Sold (Solderi ering ng Iron Iron,, Screw Screw Dri Driver ver Set Set,, Tweezer, No Nose Pl Plier, Cu Cutter, Ha Hammer, Fi File, De Desolder Pu Pump, Sq Squeezer).

2.

- 10 10

Electr Ele ctroni onics cs lab saf safety ety pre preca cauti ution onss (Re (Regar gardin ding g Wiri Wiring ng,, Floo Floorin ring, g, First Aid Treatment).

- 10

3.

Soldering Practice on PCB and Wiring Practice

- 10

4.

Famili Fam iliaz azati ation on and and Test Testing ing of of Electro Electronic nic comp compone onents nts like like resis resistor tor,, capacit capacitor or,, inductor, transformer, loud speaker, semi conductoring devices like diode, Transistor, IC Packages

5.

- 10

Stud St udy y of of pow power er su supp pply ly st stag agee in in Rad Radio io Re Rece ceiv iver er (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.

Stu tud dy RF Am Amp pli lifi fier er,, Mix ixeer, Loc ocaal osci cill llat ator or sta tag ge and vo vollta tage ge measu surrem emen entt

- 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 Mens ion typic typical al faults faults in a Radio Radio Rece Receiver iver and obser observe ve the the effect effect on Volta Voltage ge data and performance of the Radio Receiver

14.

- 10

Study Stud y of Pub Public lic Ampl Amplifie ifierr system system and mea measure suremen mentt of stan standard dard volt voltage agess 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 Engg Lab

Recommend Documents