1

Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:1& 3

Aim of experiment:Construction of a Battery Eliminator

Apparatus required

AC Plug

15-18V Transformer

Full Wave Bridge Rectifier

LM317 Voltage Regulator

Heat Sink

2200μF electrolytic capacitor

100μF electrolytic capacitor

Rotary Switch

240Ω Resistor

48Ω Resistor

336Ω Resistor

624Ω Resistor

912Ω Resistor

1488Ω Resistor (1.5KΩ is fine)

2064Ω Resistor (2KΩ is fine)

2

Theory of experiment

A battery eliminator is any device which supplies the necessary DC power to a device,

replacing the need for batteries.

For example, say if we have a device that is normally powered by batteries, such as a

calculator. It may receive 4 'AA' or 'AAA' batteries, depending on the calculator. In this

case, the DC voltage that the calculator needs is 6 volts, since 4 'AA' batteries in series adds

up to 6VDC. We can power the calculator without batteries if we supply it with the 6VDC.

So any device which allows us to bypass the use of batteries and power the device still is a

battery eliminator.

Now , we will build a simple, effective battery eliminator which supplies many of the typical

voltages that batteries would, only without the need for batteries.

Battery Eliminator Schematic Diagram

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a battery eliminator, it creates DC voltage from the AC mains voltage from a wall outlet. To

build a battery eliminator, purchase a 3-prong AC plug. It can also work with a two-prong AC

plug. But having a 3-prong plug is better because ground provides

better against possible electric fires.

Transformer- After the AC plug, we need a step-down

transformer. The tranformer's job is to take the 120V AC We'll

now go over each part of this circuit and go over the role each

component plays, so that you can know how this circuit works in

its entirety.

AC Plug- The first part of the circuit is the AC plug. When we create voltage from the mains

line and step it down to 15-18 volts. This is because our battery eliminator will supply variable

DC voltage of 1-20V. Therefore, we lower the very high voltage that we get from the mains

outlet from the wall into a smaller voltage. It must still exceed the voltage of the DC which we

want to output. Since we want to create up to 20VDC variable voltage output, we need a

transformer that converts the mains voltage to a voltage that is higher than this 20V. A step-

down transformer is a great device for lowering voltage from a mains AC voltage line.

Full-wave Rectifier- The next component we need in our circuit is a full-wave rectifier. The job

of the full-wave rectifier is to take the AC voltage from the transformer and rectify it so that the

voltage no longer goes through a negative cycle. With the rectifier, all of the voltage is rectified

positive.

Smoothing Capacitor- The next component after the full-wave rectifier is the smoothing

capacitor. The smoothing capacitor acts to smooth out fluctuations in a signal, so that there is

less fluctuation. As you saw in the previous component, the rectifier creates pulsating DC

signals. The smoothing capacitor, now, a 2200μF capacitor, acts to even out this pulsating

fluctuations to create a smoother waveform.

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The diagram below shows how the voltage waveform looks before and after the smoothing

capacitor:

LM317 Voltage Regulator- After the smoothing cap is the LM317 Voltage Regulator.

This regulator serves a twofold purpose. First, it serves to further smooth out the fluctuating

signal, so that it's a perfectly smoothing DC signal.

A regulator is a device that "regulates" voltage so that a perfectly smoothing DC voltage is

output.

Below is a diagram of a voltage waveform after both a smoothing capacitor and a voltage

regulator:

The second purpose of the LM317 regulator, since it is an adjustable voltage regulator, is to

produce variable DC voltage as output. How we vary voltage is by flipping the rotary switch to

the voltage we desire outputted.

Rotary Switch- We need a rotary switch so that we can connect to different resistances in the

circuit. The different resistance values allow us to change the DC voltage which is output by the

battery eliminator. The rotary switch allows us to switch between different voltages.

Since we are connecting between 6 different voltages, we need a 6-position rotary switch. If you

can't find a 6-position one, then use one with more and then just leave those empty terminals

open, with nothing connected to them.

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Resistors Connected to Rotary Switch- We attach resistors to the rotary switch, S1, to create

different voltage outputs at each of the terminals of the switch. We use 48Ω, 336Ω, 624Ω, 912Ω,

1488Ω, and 2064Ω resistors. The reason we use these resistors is because the output voltage

created by the LM317 voltage regulator is produced according to the formula, VOUT= 1.25V (1

+ R2/R1). The recommended resistor value to use for R1 by the manufacturer is 240Ω. So this

resistor value is fixed. To create different output voltages, we vary the value of resistor R2. By

making R2 48Ω, we create 1.5V as output. By making the value 336Ω, we create 3V as output.

By making the value 624Ω, we create 4.5V as output. By making the value 912Ω, we create 6V

as output. By making the value 1488Ω, we create 9V as output. By making the value 2064Ω, we

create 12V as output.

We realize that getting resistors of value 1488Ω and 2064Ω is difficult, so you can get use

1.5KΩ and 2KΩ as replacements to simplify the value.

Again, these resistance values are what create the various output voltages.

Heat sink- One thing we must do to the voltage regulator is attach a heat sink to it. This is vital

for this application.

This is because when we use a regulator, we input a voltage into it and it outputs the voltage,

based on the values of resistor R1 and the resistance value which the rotary switch is connected

to. When the rotary switch is connected to its highest resistance, it doesn't dissipate that much

heat. Since our transformer outputs 15-18V, when the rotary is set to 2.6KΩ, the regulator

outputs 12V. 15-12V=3V. Thus, not that much wasted voltage is created. However, if the

potentiometer is set to 48Ω, the regulator outputs approximately 1.5. 15V-1.5V= 13.5V of

wasted, dissipated energy. This creates a lot of heat, since the voltage difference between input

and output voltage is so great. Any difference appears as heat. So the greater the difference, the

greater the heat. This is the r reason it is vital to attach a heat sink to the regulator. When the

difference between input and output voltage is great, it appears as heat. We must have a way to

dissipate this heat, or else it can damage or destroy the circuitry of the battery eliminator. The

way to do this is to use a heat sink.

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C2 Capacitor- The C2 capacitor acts again as a load balancer. It helps to smooth out any

fluctuations that may exist on the output of the regulator.

And this is how a simple battery eliminator can be built that allows for voltage adjustment.

Conclusion:

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Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:1 & 3

Aim of experiment: Construction Assembling of a Stabilizer

Apparatus required

Resistor R1 & R2 = 10KΩ

Resistor R3 = 470KΩ

Variable Resistor = 10KΩ

Capacitor C1 = 1000 µF/25 V

Diode D1 & D2 = 1N 4007

Zener Diode Z1 & Z2 = 4.7 V/ 400mW

Transformer TR1 = 0V - 12 V , 500mA

Transformer TR2 = 9V-0V-9V, 5A.

Op-Amp = LM 741

Transistor = BC 547

Relay = DPDT, 12V, 200Ω.

LED = Red (1)

Voltmeter = 1 Pcs.

Theory of experiment

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A voltage stabilizer is a device which is used to sense inappropriate voltage levels and correct

them to produce a reasonably stable output at the output where the load is connected. Here we

will study the design of a simple automatic mains AC voltage stabilizer which can be applied for

the above purpose. Referring to the figure we find that the whole circuit is configured with the

single op amp IC 741. It becomes the control section of the whole design. The IC is wired as a

comparator, we all know how well this mode suits the IC 741 and other op amps. It's two inputs

are suitable rigged for the said operations. Pin #2 of the IC is clamped to a reference level,

created by the resistor R1 and the zener diode, while pin #3 is applied with the sample voltage

from the transformer or the supply source. This voltage becomes the sensing voltage for the IC

and is directly proportional to the varying AC input of our mains supply. The preset is used to set

the triggering point or the threshold point at which the voltage may be assumed to be dangerous

or inappropriate. We will discuss this in the setting up procedure section. The pin #6 which is the

output of the IC, goes high as soon as pin #3 reaches the set point and activates the

transistor/relay stage. In case the mains voltage crosses a predetermined threshold, the ICs non

inverting detects it and its output immediately goes high, switching ON the transistor and the

relay for the desired actions. The relay, which is a DPDT type of relay, has its contacts wired up

to a transformer, which is an ordinary transformer modified to perform the function of a

stabilizer transformer. It’s primary and secondary windings are interconnected in such a manner

that through appropriate switching of its taps, the transformer is able to add or deduct a certain

magnitude of AC mains voltage and produce the resultant to the output connected load.

The relay contacts are appropriately integrated to the transformer taps for executing the

above actions as per the commands given by the op amp output. So if the input AC voltage tends

to increase a set threshold value, the transformer deducts some voltage and tries to stop the

voltage from reaching dangerous levels and vice versa during low voltage situations.

Circuit Diagram:

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Operation:The proposed simple automatic voltage stabilizer circuit may be set up with the

following steps: Initially do not connect the transformers to the circuit. Using a variable power

supply, power the circuit across C1, the positive goes to the terminal of R1 while the negative

goes to the line of 39 D2’s cathode. Set the voltage to about 12.5 voltage and adjust the preset so

that the output of the IC just becomes high and triggers the relay. Now lowering the voltage to

about 12 volts should make the op amp trip the relay to its original state or make it de-energized.

Repeat and check the relay action by altering the voltage from 12 to 13 volts, which should make

the relay flip flop correspondingly. Your setting up procedure is over. Now you may connect

both the transformer to its appropriate positions with the circuit. Our simple home made mains

voltage stabilizer circuit is ready. When installed, the relay trips whenever the input voltage

crosses 230 volts, bringing the output to 218 volts and keeps this distance continuously as the

voltage reaches higher levels. When the voltage drops back to 225, the relay gets de-energized

pulling the voltage to 238 volts and maintains the difference as the voltage further goes down.

The above action keeps the output to the appliance well between 200 to 250 volts with

fluctuations ranging from 180 to 265 volts.

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Limitation:

When installed, the relay trips whenever the input voltage crosses 230 volts, bringing the

output to 218 volts and keeps this distance continuously as the voltage reaches higher

levels.

When the voltage drops back to 225, the relay gets de-energized pulling the voltage to

238 volts and maintains the difference as the voltage further goes down.

The above action keeps the output to the appliance well between 200 to 250 volts with

fluctuations ranging from 180 to 265 volts.

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Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:2

Aim of experiment: Soldering Practice: Connecting circuit components

Apparatus required

The basic tools that are used for this purpose are

Soldering Iron

Solder Wire [Alloy]

Flux

PCB and the components that are to be soldered

The soldering iron is the heat source tool for the process. It should be of high quality. Of course

the price may increase with the quality, but the soldering will be perfect. Usually a 25 Watt

soldering iron is adequate for the process. A higher watt device may bring too much heat to the

PCB and will surely damage the sensitive components. A lesser watt device may not have

adequate heat and thus is prone to be extensively used. This may also cause extensive heat

damage.

The solder wire is used to fix the components like resistors, capacitors and so on to the PCB in

the given fields. The leads of the devices are connected to the track of the PCB by melting the

soldering wire to the junction. When the heat from the soldering iron touches the soldering wire

it starts melting and this melted wire when introduced to the junction, joins the components to

the track firmly.

The soldering wire is actually an alloy of tin and lead in the ratio 60:40. This is the best ratio that

is considered for soldering in PCB’s. There are other proportions of this alloy and they are

considered low quality as the tin content with respect to lead will be lower.

A high quality solder wire will have a melting point of about 250 degree Celsius and will have a

very high conductivity along with a shiny appearance. When a high quality solder wire is used

to connect the components to the PCB, there is to be no fear of corrosion in future.

Flux is another important component that is used in soldering purposes. It is sealed to the core of

the solder wire before soldering. The flux is used to reduce the surface tension of the solder wire

in its melting point. Thus, it acts as a wetting agent and wets the parts that are to be joined to the

PCB. This also helps in the proper heat transfer from the solder iron to the solder wire.

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Another main use of the flux is to prevent oxidation of both the solder wire and the components

that are added to the PCB. The Tin-Lead alloy that is used as solder wire may have no problem

when attached to copper. But they do not attach so well, when in contact with the oxides of

copper. The oxides of copper mostly form when the temperature is increased for soldering. The

flux can prevent the formation of metal oxide as they are nearly inert at room temperature and

become strongly reduced when the temperature increases. The use of flux causes the rise of

smoke when the soldering process continues. During this time the flux acts as a catalyst and

helps in removing the oxidants and thus cause a better solder joint.

Soldering Technique

Here is the step by step procedure for soldering.

1. By that time the solder iron may get heated to the optimum temperature [250 degree Celsius].

2. Bend the leads of the different devices that are to be connected to the PCB. For a clean bend, the

approximate distance of bend is about 2mm from its body ends.

3. If you are connecting a resistor to the PCB, find its spot and place it into the hole of the PCB.

4. After placing the resistor flip the PCB in such a way that the inserted leads looks towards you.

5. Take the soldering iron in the right hand and the solder wire in the left hand. The solder wire

must be placed on your finger tips with about 3 inches extending from your finger grip.

6. Bring both the solder iron tip and the solder wire tip close to the base of the lead of the resistor

and copper track of the PCB. Make them come in contact at the same instant at the junction.

7. You will notice that the solder wire starts to melt as soon as the contact is made.

8. When the wire starts melting keep pushing it till the joint has been filled up with the molten

alloy.

9. Move away the solder wire and the solder iron simultaneously and allow the molten wire to

solidify. Thus one lead of the resistor has been connected to the PCB. Do the same step for the

other lead and also for all other components.

The setp by step procedure is also shown in the figures given below.

10. Soldering Techniques

11.

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Precautions to be taken while Soldering

For a good heat transfer, the solder wire and the solder iron must be well cleaned before starting.

It must also be pre-tinned with solder. In order to avoid the overheating of PCB, the components

are usually elevated above the PCB. After the component is inserted in the PCB hole, the excess

lead is cut off, thus leaving a length of about the radius of the pad.

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After soldering, the soldered joints must also be cleaned after it has been solidified.

Some components that are to be soldered may be heat sensitive. For such components a heat sink

may be used on the leads which will reduce the heat transfer to the components. The only

problem is that for such components more heat will be required from the solder iron to complete

the joint.

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Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:4

Aim: Assembling Inverter

Theory:

An inverter is a device that changes D.C. voltage into A.C. voltage. A direct current (D.C) is a

current that flows in only one direction, while an alternating current (A.C.) is that which flows in

both positive and negative directions.

The inverter performs the opposite function of a rectifier formed in the late nineteenth century

through the middle of the twentieth century; DC to AC power conversion was accomplished

using rotary converters or motor-generator sets (M-G set).

The origins of electromechanical inverters explain the source of the term inverter. Early A.C to

D.C converters used an induction or synchronous AC motor direct – connected to a generator

(dynamo) so that the generators commutator reversed its connections at exactly the right

moments to produce DC. A later development is the synchronous converter, in which the motor

and generator windings are combined into one armature, with slip rings at one end and a

commutator at the other end only one field frame.

Transformer:

It is an inductively coupled circuit used for transmitting alternating current energy. It is also used

for matching impedance between the generator and the load. It makes use of mutual inductance

in which a current flowing in a coil produces a varying electromagnetic wound over the primary

coil.

Most transformers are used to step-up or step down voltage or current. The number of turns on

the primary winding is usually different form that of Secondary. However, an isolation

transformer provides secondary voltage and current that is same as that of primary voltage and

current, because both winding have the same number of turns, (Expect for resistive losses).

These transformers prevent the transfer of unwanted electrical noise from the primary to the

secondary winding.

The primary and secondary windings of conventional transformer for electronic application are

wound on tubular bobbin (insulated spool that serves as a support for the coil) made of plastic

and other insulated materials. The wound bobbins are then enclosed by iron or steel cores in the

shape of figure start of “E” and “I” shaped laminated metal sheets, assembled through and round

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the wound bobbins. The laminations are then clamped down to form a rigid assembly; some

transformers have plastic shrouds to insulate the windings from the core. Both primary and

secondary windings can be wound on the same bobbin, but it is now common practice, to wind

the primary and secondary windings separately on a split bobbin, to improve electrical isolation.

The primary and secondary terminals may be connected to rigid pins on the bobbin that also

functions as printed circuit board mounting pins.

Mosfet:

Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is a three terminal device they

can be used either as an amplifier or as a switch. MOSFETs are classified as enhancement a

depletion types.

Battery:

It is a d.c. power source to electrical or electronic equipment or devices that make use of it.

Battery is being made available as direct source of energy. It is therefore necessary to select a

reliable battery for optimum performance.

Light Emitting Diode:

It radiates optical energy when forward biased. LED is divided into base on the type of optical

energy it radiates. The visible LED provides a useful means of indicating the state of a circuit

and is therefore used as an indicator. In order to use visible LED as an indicating there is a need for the

use of a protective resistor, which serves as a potential divider as shown below. The invisible/infrared

LED radiates infrared light when forward biased. It is used in conjunction with the photodiode

phototransistor to form a sensing system as in the remote control circuit.

2. INVERTER DESIGN AND CONSTRUCTION

The inverter is a two operation modes device, the inverting and the charging modes. The

inverting mode comprises of the oscillator, the driver, the output (MOSFET) section, the PWM

section, low battery / overload protection circuit, and the transformer. The charging mode

implements the transformer, the FET‟s (internal diodes) and the charging control circuit. A third

operation mode is the changeover modes for switching between the two aforementioned modes

at times of auto-back up for power failure and power restoration for the charging process. This

mode implements a delay circuit, electromagnetic relays and power supply circuit.

3. TRANSFORMER DESIGN

A transformer is a device that couples two AC circuits magnetically and provides electrical isolation

between the circuits while allowing a transformation of voltage and current from one circuit to another i.e.

it is mainly used for voltage and current transformation .

The Generated E.M.F in a Wounded Transformer

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In observing an ideal transformer with secondary opened and the primary connected to a

sinusoidal alternating voltage V1, the potential different causes an alternating current to flow in

the primary since primary coil is purely inductive and has no output but draw the magnetizing

current I only .And this I will function as to magnetized the core in the secondary .It is small in

and lag voltage V1 by 900. It therefore produces an alternating flux that is proportional to the

current inputs. This flux is linked by both primary and secondary windings .Thus; this leakage(s)

produced a mutually induced e.m.f E2 in secondary winding that anti-phase with V1 and has

magnitude proportional to rate of change of flux and the number of secondary turns.

Let N1=Number of turns in primary, N2=number of turns in secondary

The transformation ratio, K= N1/N2

The equation for the voltage and current transformation of a transformer is given by K= V2/V1= I1/I2

F=Frequency of A.C input (Hz)

Maximum flux in core (Webbers) =B*A

Average rate of change of flux =maximum. Flux divided by 1/4F. (Wb/s or Volt.)

Now rate of change of flux per turn means induced e .m .f in Volt

Thus Average e.m. f /turn =4*F*max. Flux

Since the flux is sinusoidal

r.m.s =form factor*Average e.m.f /turn

But form factor =r.m.s value /Average value=1.11,

Then r.m.s value of E.m.f =1.11*4F*max. Flux =4.44F*max. Flux ,

But max .flux =Bm*A r.m.s value of E.m .f in primary turn (Tp) =4.44F*Bm*A*Tp

NOTE: Bm is assumed to be 15000Wb/m. F=50 Hz By introducing stacking factor (10-8) and Tp

factor (0.9) then we have Number of turns per volt, NT.V-1= 7/A

But form factor =r.m.s value /Average value=1.11, Then r.m.s value of E.m.f =1.11*4F*max. Flux

=4.44F*max. Flux , But max .flux =Bm*A r.m.s value of E.m .f in primary turn (Tp)

=4.44F*Bm*A*Tp NOTE: Bm is assumed to be 15000Wb/m. F=50 Hz By introducing stacking

factor (10-8) and Tp factor (0.9) then we have Number of turns per volt, NT.V-1= 7/A

4. CHOICE OF TRANSFORMER’S COMPONENTS

The power Rating for the Inverter transformer (KVA) =1.0KA , E2=12V

Assuming the efficiency of transformer =85%

Then Input rating =output /Efficiency=1000VA/0.85=1176VA

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Ip = PI / VP VP = 260V

Ip = 1176 / 260 = 4.5A

Is = Po / Vs Vs = 12V

Ip = 1000 / 12 = 83.3A

5. 50 Hz FREQUENCY OSCILLATOR SECTION

The generation of 50 Hz frequency by the oscillator section is based on the application of a

PWM controller IC SG3524

6. SG3524 DESCRIPTION

7. THEORY OF OPERATION

Voltage Reference

An internal series regulator provides a nominal 5V output which is used both to generate a

reference voltage and is the regulated source for all the internal timing and control circuitry. This

reference regulator may be used as a 5V source for other circuitry. It provide up to 50mA of

current itself and can easily be expanded to higher current with an external PNP

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Oscillator

The oscillator in the SG3524 uses an external resistor (RT) to establish a constant charging

current into an external capacitor (CT). While this uses more current than a series-connected RC,

it provides a linear ramp voltage on the capacitor which is also used as a reference for the

comparator.

8. THE OSCILLATOR SECTION

The schematic diagram of the oscillatory section is as shown in fig. 2. IC1 SG3524 is used to

generate the 50 Hz frequency required to generate AC supply by the inverter. Battery supply is

connected to the pin-15. Pin-8 of the IC1 is connected to negative terminal of the battery. Pin-6

and 7 of IC1 are oscillator section pins.

9. DRIVER SECTION

MOS drive signal from pin-11 and 14 of IC1 are coupled to base of transistors T1 and T2. This

result in the separation of the signal into two different channels and an amplification of the signal

to a sufficient level output from the transistors emitter. The resulting MOS drive signal at emitter

of T1 and T2 is coupled to the gate of each MOSFET in the first and second MOSFET channels

respectively. The driver section made up of T1 and T2 circuit is incorporated into the oscillator

Fig 2. Oscillator Circuit Diagram

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10. OUTPUT SECTION

The 50Hz alternating MOS drive signal reaching the MOSFET channel separately results in the

channels being alternatively ON and OFF. Drain (D) of all the MOSFET of one channel is

connected together and one end of the inverter bifilar winding is connected to this connection.

The same is done to the second channel and the other end of the inverters winding. Positive

terminal of the battery is connected to the centre tapping of the bifilar winding. Source (S)

terminal of each MOSFET is connected to the negative terminal of the battery. Because polarity

of the 50Hz MOS drive signal at pin-11 and 14 are alternatively different, current flows through

the first half and second half of the transformer‟s bifilar winding alternatively.

Fig.3. Output Section Change Over Circuit

The alternating current flowing will induce an AC current of 50Hz in the 260V tapping of the

transformer. This tapping is connected to N/O-2 terminal of relay. When the AC mains is not available,

pole P-2 of the relay is connected to N/O-2 terminal and thus the AC voltage produced by the inverter

reaches the inverter output socket. The output section changeover circuit is as shown in fig. (3).

11. PULSE WIDTH MODULATION PWM SECTION

PWM is used to keep the inverter output to a constant 220V AC irrespective of a change in the load value

connected to the inverter output socket. PWM is realized by feeding back the AC supply generated by the

inverter to the PWM IC1 to keep the pulse width output from pin-11 and 14 constant. To provide

feedback to the PWM controller IC, a bridge rectifier circuit made of four diodes (D2, D3, D4 and D5) is

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connected to the drain of the MOSFET channels. The DC voltage from the bridge rectifier is filtered by a

10μF capacitor and given to pin-1 of PWM IC through a potential divider circuit made of 10k and PWM

adjustment preset VR2. The PWM circuit has also been incorporated into the oscillator schematic

diagram as shown in fig. (2). Pin-1, 2 and 9 are three pins of an internal Op-Amp, pin-1 and 2 are input

pins and pin-9 is the output pin. Pin-1 is given the feedback signal; pin-2 is given 2.5V regulated supply

as reference voltage through voltage divider circuit of two 10K resistors. The reference voltage is taken

from pin-16 of the PWM IC1. Pin-9 is internally connected to the section that controls the width of the

oscillating frequency. Change in signal at pin-9 will result in a change in the width of the output

frequency and this will always bring back the inverter output to its original 220V.

12. LOW BATTERY / OVERLOAD PROTECTION CIRCUIT

The low battery and overload protection circuit is a protection circuitry that protects the

battery from being over drain and inverter‟s transformer and MOSFET from being damaged

respectively. The low battery and overload shutdown circuit are built upon Op-Amp

comparator application.

Overload Protection Circuit

The overload protection circuit uses two Op-Amps A and C made of pin-6, 7, 1 and pin-10,

11 13 of IC2 (LM339) respectively

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Battery Charging Control Section

In this mode, the inverter transformer works as a step-down transformer and output 12V at

its secondary winding. During charging, MOSFET at the output section works as rectifier

(due to internal diodes), the drain being the cathode and the source as anode. The center

tapping of the transformer is connected to the positive terminal of the battery and the

MOSFET source is connected to negative terminal of the battery. When the inverter receives

AC mains supply, inverter transformer and MOSFET together works as a charger and

charge the battery.

The battery charging control circuit is as shown in fig. 7. In other to protect the battery from

being over charge and the MOSFET from sudden surge current at the start of charging when

power is restored, two other circuits are incorporated; the soft start section and charging

voltage sensing sections.

13. CHARGING VOLTAGE SENSING SECTION

The charging voltage sensing section makes use of Op-Amp A and B of IC3 (LM393), SCR Q2,

transistors T6 and T7. Pin-2 and 6 of IC3 is given a constant reference voltage of 5.6V through 47k

resistor. Pin-3 is given positive supply from the battery through divider circuit of 5k and 7k resistor.

When the charging battery voltage is below 12V, pin-2 voltage is higher than pin-3 voltage and thus

Op-Amp A of IC3 ramps low which biases transistor T6. The voltage at the collector of T6 provides

the trigger current IT for SCR Q2 through 1k resistor. Q2 switches ON (conduct) and 8V battery

charging signal is available at cathode used for the following;

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Once Q2 is fired, charging continues until the voltage at pin-5 of IC3 passes a voltage level

of 5.6V when the battery is charged beyond 14.5V. At charging battery Volt of 14.5V, pin-5

of IC3 becomes more positive than pin-6 thus op-amp B ramps high to bias transistor T7.

The switching of T7 reduces the holding current IH of Q2 to zero and Q2 stops conducting.

Q2 remains in the off state until battery voltage fall below 12V when charging starts again.

Charging continues till 14.5V is reached. In this way, the battery charge is topped at interval

to keep the battery voltage level before power failure. This is incorporated in fig. 6 battery

charging control circuit.

14. CHANGEOVER POWER SUPPLY SECTION

The circuit diagram of the changeover power supply circuit for the relays is shown in fig 7.

The transformer steps the 220Vac voltage down to 12Vac that is rectified by the bridge

rectifier and filtered by the 1000μf capacitor. The supply increases to 16V after filtration.

The supply is regulated by LM7812 to keep the voltage for relay switching constant at 12V.

15. COMPONENTS SELECTION

T2 – 220V/12V 500mA: The 12V transformer in conjunction with the filter capacitor

(1000uf/25V) and regulator (LM7812) guaranteed that 12V was available to switch the relays

when the mains voltage is restored.

Full Wave Rectifier: Four diodes, D1 – D4 (IN4007) were used to convert the ac voltage

available at the secondary of the power supply circuit to dc. The IN4007 diodes are suitable for

the circuit because of its rating (PIV - 1000V, Average Rectified output current for resistive load

– 1A, and Non repetitive peak surge current for one cycle – 30A)

24

Filter Capacitor: the 1000μf /25 capacitor is used to filter the ripple levels present in the

rectifier voltage. The values of the capacitor used with a 50Hz supply may range from 100uf –

30,000uf depending on the load current and the degree of smoothening required. In selecting

capacitors, the ripple voltage required is 10% of the peak value. The selection of this capacitor is

based on the following calculation.

17. PERFORMANCE EVALUATION

Table 4.1. Settings on the Inverter

Inverter output voltage

Inverter frequency

Minimum battery voltage

Maximum loading capacity

Minimum A.C. input voltage

Maximum A.C. input voltage

Table 4.2. Load Test

Power (watt)

Voltage (v)

16. MAINTENANCE, SAFETY AND PRECAUTION

1. Dead batteries should not be used with the inverter

2. The battery terminals should not be removed too often. When it is removed, replacement of

correct polarity must be ensured.

3. The inverter must be put in a moderate temperature environment.

4. The inverter should always be shut down when not in use

25

5. The inverter should always be partially loaded (not more than 80% of its maximum capacity

will be enough).

6. The use if inductive loads like refrigerator, induction machine e.t.c. on the inverter should be

avoided.

7. The input plug of the inverter should be plugged to a three-pin, properly earthed socked.

18. CONCLUSION

26

Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:5

Aim:

AC Adapter Troubleshooting and Repair

AC Adapter Testing

AC adapters can easily be tested with a VOM or DMM. The voltage we measure (AC or DC)

will probably be 10-25% higher than the label specification. If we get no reading, wiggle,

squeeze, squish, and otherwise abuse the cord both at the wall wart end and at the device end.

We may be able to get it to make momentary contact and confirm that the adapter itself is

functioning.

The most common problem is one or both conductors breaking internally at one of the ends due

to continuous bending and stretching.

Make sure the outlet is live - check with a lamp.

Make sure any voltage selector switch is set to the correct position. Move it back and forth a

couple of times to make sure the contacts are clean.

If the voltage readings check out for now, then wiggle the cord as above in any case to make sure

the internal wiring is intact - it may be intermittent.

Although it is possible for the adapter to fail in peculiar ways, a satisfactory voltage test should

indicate that the adapter is functioning correctly.

It's also possible that the power jack on the device itself is damaged from use or abuse. If

possible, confirm proper operation with a COMPATIBLE adapter. With battery operated

devices, there is usually a set of contacts that should close when the adapter is removed to

connect the internal battery to the circuitry. If these don't operate properly, the device may not

work off batteries (they may appear to not be charged), the AC adapter, or both. Check the jack

27

for obvious signs of damage (cracked, loose, etc.). A squirt of contact cleaner into the jack may

clear up intermittent contact problems not due to actual damage.

AC Adapter Repair

Although the cost of a new adapter is usually modest, repair is often so easy that it makes sense

in any case.

The most common problem (and the only one we will deal with here) is the case of a broken wire

internal to the cable at either the wall wart or device end due to excessive flexing of the cable.

Usually, the point of the break is just at the end of the rubber cable guard. If we flex the cable,

we will probably see that it bends more easily here than elsewhere due to the broken inner conductor. If we are reasonably dextrous, we can cut the cable at this point, strip the wires back

far enough to get to the good copper, and solder the ends together. Insulate completely with

several layers of electrical tape. Make sure we do not interchange the two wires for DC output

adapters! (They are usually marked somehow either with a stripe on the insulator, a thread inside

with one of the conductors, or copper and silver colored conductors. Before you cut, make a note

of the proper hookup just to be sure. Verify polarity after the repair with a voltmeter.

The same procedure can be followed if the break is at the device plug end but we may be able to

buy a replacement plug which has solder or screw terminals rather than attempting to salvage the

old one.

Once the repair is complete, test for correct voltage and polarity before connecting the powered

equipment.

This repair may not be pretty, but it will work fine, is safe, and will last a long time if done

carefully.

If the adapter can be opened - it is assembled with screws rather than being glued together - then

we can run the good part of the cable inside and solder directly to the internal terminals. Again,

verify the polarity before we plug in our expensive equipment.

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 :

28

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, 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.

29

Results :

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

FAULTS IN INVERTER

Aim :

Mension the faults in Radio Receiver and observe the effects on voltage data and performence of the radio receiver.

Equipment needed :

AC multimeter, inverter kit, power supply and connecting wires.

30

Inverter

Theory & Procedure :

If the inverter appear to be malfunction following procedure should be followed to eliminate any

external problems.

1.Turn the Inverter “OFF” via the circuit breaker switch on the front panel.

1. Disconnect all AC wiring from the Inverter.

2. Disconnect DC Battery leads from Battery.

3. Clean Terminals (remove all grease and or corrosion on both DC leads and battery terminals

31

4. Ensure we have sufficient battery capacity at the nominal voltage (specified on the

compliance label at the rear of our Inverter). Please note: Use minimum 60AH battery or the

size of a substantial car battery.

5. Make connection direct to battery terminals and insure all connections are tight.

6. Ensure battery voltage is within the correct limits as outlined in the section ELECTRICAL &

MECHANICAL SPECIFICATIONS of this manual. If we do not have a DC voltmeter or

multimeter check the front panel for overvolts and undervolts LED’S.

7. Turn the Inverter “ON” via the circuit breaker switch on the front panel. Observe the lights

on the front left of your Inverter. Refer to sections INVERTER OPERATION for

explanation of lights and / or section FAULT FINDING CHART.

8. Plug in various appliances and monitor the Inverters operation.

Important must be remembered

• Remember that it has automatic start with load.

• Make sure leads and terminals are not corroded or faulty in any way.

• Make sure the Inverter goes into Standby with no load switched on.

• Make sure the circuit breaker is reset properly. If unsure switch “OFF” and “ON” again.

• When measuring the AC output of Modified Squarewave Inverters use a TRUE RMS VOLT

METER. Average reading meters will not give an accurate measurement. (240V RMS =

210V average) depending on Battery voltage and load

32

Symptom Cause a

Action

No LED on. Is Circuit Breaker switched on? Switch OFF and ON.

No output power. Is input voltage present? Check battery connections.

Was too high DC Voltage left on Inverter ie. from PV If voltage exceeds more than triple the Inverter input voltage, damage

Modules or battery charger may have occurred.

Inverter does not go back to Stand by Inverter senses load present.

Disconnect all loads. Disconnect leads on junction box on back of

mode Green LED does not Inverter.

flash. Auto Start set too low. Turn Auto Start clockwise.

Inverter overloads constantly. Inverter overheated due to a large load being run. Check if case is hot, allow 5 minutes to cool down, reset Inverter via

circuit breaker.

Current draw from battery is excessive due to a short Disconnect all AC 240V wiring from Inverter, check if Green LED

circuit on 240V AC side or load to be started is too flashes .

large.

Fluorescent Lights are used with power factor Remove capacitors (MSW only)

correction capacitors

If any lightning has occurred unit might be damaged. Return to supplier.

Inverter constantly shuts down in Battery voltage below specified limit. Check battery connections and state of charge (should be above SG

undervolts. level of 1220)

Battery voltage drops below limit only when load is Check size of load, might be too large for battery to handle. Check

being connected. connections! Check DC wiring between Inverter and battery for any

defects!

Inverter constantly shuts down in Battery voltage above specified limit. Battery might be overcharged.

overvolts. Battery charger imposes high ripple peak voltages Check battery charger.

across battery terminal which may exceed limit for short periods.

Solar panels are connected to Inverter without Open circuit voltage of solar panels exceeds limit. Check system.

batteries.

Solar regulator causes voltage peaks across battery Check solar regulator for this symptom. This only occurs during peak

terminals. sun periods and when load demand on system is very low, ie. during

holiday periods.

Battery Charger without regulation circuit and or choke

Battery bank might be too small to soak up these currents. The

is connected to the battery which imposes very high detection circuit of the Inverter works within a time frame of 0.1 second

peak currents. to detect this fault condition. Check float voltage.

33

Symptom Cause Action

Inverter does not sense load Load too small for inverter to

sense. I/e. compact

Adjust Auto Start anti clockwise or run other load at the same time or

fit

(MSW only) fluros without electronic ballast! PTC Sense resistor. Use PL

lamps.

Inverter switches on with load but Current draw of load changes. ie.

small battery

Auto Start also depends on battery voltage to some extent.

Run other

drops out occasionally. chargers. small load at the same time.

Inverter starts up correctly ie. Green

Current flow causes voltage drop on Battery

Check battery connections and fuse connections. Connect

inverter

light on then flashing; but shuts connections. straight to battery terminal.

down when load applied

AC Output voltage too low Average reading meters will not

give an accurate Use TRUE RMS volt meter..(MSW only)

measurement of Modified

Squarewaves. (240V RMS =

210V average) depending on

Battery voltage and load

Conclusion:

34

Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:6

Aim: Location of faults in different types of Electronics Circuits.

Apparatus :

Digital Multimeter

Analog Multimeter

ohms meter

flyback tester

Theory: While many digital multimeters these days have a specific capability for testing diodes

and sometimes transistors, not all do, especially the older analogue multimeters that are still in

widespread use. However it is still quite easy to perform a simple go / no-go test using the

simplest of equipment.

This form of testing is able to detect whether transistor or a diode is operational, and although it

cannot provide details of the parameters, this is seldom a problem because these components will

have been tested at manufacture and it is comparatively rare for the performance to fall to a point

where they do not operate in a circuit. Most failures are catastrophic, rendering the component

completely inoperable. These simple multimeter tests are able to detect these problems very

quickly and easily.

Procedure:

The basic diode test is very simple to perform. Just two tests are needed with the multimeter to ensure that the

diode works satisfactorily:

35

... the band on the diode package represents the cathode....

The method of testing a diode with an analogue meter is quite straightforward.

Step by step instructions:

1. Set the meter to its ohms range - any range should do, but the middle ohms range if several are available is

probably best.

2. Connect the cathode terminal of the diode to the terminal marked positive on the multimeter, and the anode

to the negative or common terminal.

3. Set the meter to read ohms, and a "lowish" reading should be obtained.

4. Reverse the connections.

5. This time a high resistance reading should be obtained.

Notes:

In step 3 above the actual reading will depend upon a number of factors. The main thing is that the meter

deflects, possibly to half way or more. The variation depends on many items including the battery in the

meter, and the range used. The main point to note is that the meter deflects significantly.

When checked in the reverse direction, silicon diodes are unlikely to show any meter deflection

whatsoever. Germanium ones that have a much higher level of reverse leakage current may easily show a

small deflection if the meter is set to a high ohms range.

This simple analogue multimeter test of a diode is very useful because it gives a very quick indication of

whether the diode is basically operational. It cannot, however, test more complicated parameters such as the

reverse breakdown, etc.

36

How to test a transistor with a multimeter

The diode test using an analogue multimeter can be extended to give a simple and straightforward confidence

check for bipolar transistors. Again the test using a multimeter only provides a confidence check that the

device has not blown, but it is still very useful.

The test relies on the fact that a transistor can be considered to comprise of two back to back diodes, and by

performing the diode test between the base and collector and the base and emitter of the transistor using an

analogue multimeter, the basic integrity of the transistor can be ascertained.

37

It should be noted that a transistor cannot be functionally replicated using two separate diodes because the

operation of the transistor depends upon the base which is the junction of the two diodes, being one physical

layer, and also very thin.

Step by step instructions:

The instructions are given primarily for an NPN transistor as these are the most common types in use. The

variations are shown for PNP varieties - these are indicated in brackets (.. .. ..):

1. Set the meter to its ohms range - any range should do, but the middle ohms range if several are available is

probably best.

2. Connect the base terminal of the transistor to the terminal marked positive (usually coloured red) on the

multimeter

3. Connect the terminal marked negative or common (usually coloured black) to the collector and measure the

resistance. It should read open circuit (there should be a deflection for a PNP transistor).

4. With the terminal marked positive still connected to the base, repeat the measurement with the positive

terminal connected to the emitter. The reading should again read open circuit (the multimeter should

deflect for a PNP transistor).

5. Now reverse the connection to the base of the transistor, this time connecting the negative or common

(black) terminal of the analogue test meter to the base of the transistor.

6. Connect the terminal marked positive, first to the collector and measure the resistance. Then take it to the

emitter. In both cases the meter should deflect (indicate open circuit for a PNP transistor).

7. It is next necessary to connect the meter negative or common to the collector and meter positive to the

emitter. Check that the meter reads open circuit. (The meter should read open circuit for both NPN and

PNP types.

8. Now reverse the connections so that the meter negative or common is connected to the emitter and meter

positive to the collector. Check again that the meter reads open circuit.

9. If the transistor passes all the tests then it is basically functional and all the junctions are intact.

38

Notes:

The final checks from collector to emitter ensure that the base has not been "blown through". It is

sometimes possible that there is still a diode present between collector and base and the emitter and the

base, but the collector and emitter are shorted together.

As with the germanium diode, the reverse readings for germanium transistors will not be as good as for

silicon transistors. A small level of current is allowable as this results from the presence of minority

carriers in the germanium.

If we are in the electronic repair lab we should know that checking electronic components in

electronic boards can take up lots of our time especially if we do not know the short cut way to

test it. Many of us when starting in the field of electronic repair check each electronic component

one by one by removing it out from the board. This is the right way to test electronic components

but it is very time consuming.

We will start with resistor first. Normally the right way to test a resistor is to desolder out one lead and

then measure with digital multimeter .We can actually check a resistor while it still on board.This is true

especially when the test voltage output from our digital meter is less than 0.6 volt as it would not trigger

the surrounding semiconductors like the transistors, diodes and integrated circuits (IC). If it is more than

0.6 volt then we may not get an accurate result because our meter had triggered the surrounding

semiconductors. Another thing we need to know is that if the resistor that we are checking on board

parallel with another resistor, we will not get an exact reading. Let’s take this for example, assuming we

are checking a 470 ohms resistor on board and the measurement we get was 200 ohms plus, this means

the resistor could have been parallel with another resistor (back circuit) or surrounding circuit. If we get 0

ohms, this is very obvious that the resistor have open circuit. What if we get 2.2 megaohms? This resistor

39

is either open or has gone up in value. Other circuit components cannot possibly increase the value of a

resistor; any back circuit could only make the resistance reading lower!

Light emitting diodes or LED is very simple to check. Just connect our analog meter probe to the pins of

LED and set our meter to X1 ohm. If there is no light from the LED, just change the polarity of the probes.

We can check LED while it is still in circuit.

Voltage regulator can’t be check off board with multimeter because it is an IC (it has lots of components

inside it). We have to switch “ON” the equipment and check the output dc voltage of the voltage

regulator. First we must know what the part numbers of the voltage regulator are, and then we read the

40

specification and locate the input and output voltage and pins. For example, the general type of voltage

regulator starts with the part numbers like 7805, 7812, 7908 and etc. From the spec we would know that

pin one is input, pin 2 is ground and pin 3 is output. If there is input voltage to the voltage regulator and

no or low output voltage, suspect the voltage regulator itself faulty or something along the output line

that dragged down the output voltage.

Many switch mode power supply are using the combination of a power FET and a PWM IC design to

switch the power transformer. Whenever there is any power failure (fuse totally blown into dark color)

one will always suspect the power FET has gave way. Usually we would use the black probe set to X 1

ohms and place it to the center pin (drain) and the red probe to the gate and the source pin. This is the

same way when we want to check HOT on board. If there is a reading, chances are high that the FET has

developed a short circuit. But we also have to remember that a shorted bridge rectifier may cause the

power FET to have reading when check with the analog meter while it still on board.

41

If we get an open reading this doesn’t mean the power FET is good because a faulty FET can become

open circuit too.We don’t waste our time checking FET onboard (if the FET shorted then we can detect

right away but what if the FET open circuit?) because it is not accurate, we have no choice when comes to

testing FET, we just have to remove it out from board and test it with analog meter set to X 10k ohms.

Checking variable resistor (VR) on board is not that accurate because of the back circuit besides some VR

have their resistance code printed so small at the bottom of the VR. The best is still removing it out from

42

the circuit and test it with an analog meter. Any erratic reading can be easily seen from the analog meter

panel compares to using digital meter.

Inductor or coil testing can be done on board without removing the coil out from the circuit board. If a coil

has less loops (small coil), then we can just direct measure it with our normal ohmmeter. A small coil is

just like a wire or a jumper and it rarely become defective although it has some inductance value in it.

Testing coils that have a bigger inductance value like the B+ coil used in Monitor circuit is different from

checking the small coils. We can’t just measure the bigger coils with an ohmmeter because a bigger coils

tends to develop short circuit internally that can’t be detected by a normal meter. The meter that we use

to check the bigger coils is the Dick smith flyback tester. We can check the coils while it is still in the

circuit.

43

Checking horizontal output transistor is so easy and you can check it on board. Set our analog meter to X 1

ohm and place the black probe to the center pin (collector) of the HOT and the red probe to base and

emitter. It should not register any reading. If there is a reading, most probably the HOT has developed a

short circuit. Be aware too that components that links to the HOT like damper diode, flyback transformer,

safety capacitor, B+ circuit components and if these components go shorted it could cause our analog

meter to have reading.

44

As for the switch mode power transformer (SMPT) primary winding, we can’t accurately check it with an

ohms meter even if we already took it out from the board. We can only test it with a special type of coil

meter or the dick smith flyback tester. We can check the primary winding of the SMPT on board without

removing it out with the flyback tester. If there are any shorted components in the primary side (power

fet) or in secondary side (secondary output diodes) the flyback tester will registered a shorted reading and

the LED bars would not lit.

45

Checking the on/off power switch is the easiest one. Just place our meter probes to the switch point

(assuming the power switch have 2 leads) and set our ohm meter or continuity check function. It should

show a very low ohm resistance or the beeper will beep if we use the continuity checker. We can perform

this test even if the power switch is still in circuit. We can also use this method to test on the micro

switch.

46

Optoisolator or optocoupler IC’s usually located in between the primary and secondary side of power

supply and can be test even if the IC is still on board (you can actually test this type of IC with your

multimeter). Some of the famous optocoupler part numbers are 4N25, 4N35, PC123 and etc. Just

desolder one pin on each side (assuming this optocoupler have 2 pins on each side) of the optocoupler.

Pin 1 and 2 is the LED light and pin 3 and 4 is the phototransistor collector and emitter. Place your analog

meter probe set to X10 k ohms at pin 1 and 2 either way and it should show only one reading (low

resistance reading). This is just the exact same way as when you are checking a normal diode. If it shows 2

reading most probably it had developed a short circuit. Now place your probes to pin 3 and 4 either way

and again it will only show one reading (this time the resistance reading is a little bit high). If you got two

readings then the internal transistor may have short circuit.

47

If we want to measure an optocoupler that have 6 or even 8 pins, then we have to search for its data first

from the internet or from semiconductor data book. Once we know how the internal components are

wired, then we will use the best checking method to test them individually. Remember, a shorted

optoisolator can cause low power, no power or even power blink in switch mode power supply.

Results:

Conclusion:

48

Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:7

Aim:

Tracing fault in a CRO and its repair.

Troubleshooting Technique & Procedure:

The oscilloscope is an excellent tool for providing clues to faults within itself .In addition to the

CRT display,the calibrate signals and the front – panel indicators often provides sufficient

information to isolate the problem.

For effective troubleshooting ,examine the simple possibilities before proceeding with extensive

troubleshooting.The following list provides a logical sequence to follow while troubleshooting .

1. Check Control setting

2. Check associate equipment

3. Make a thorough visual check of the instrument.

4. Check instrument calibration

5. Isolate trouble to block level.

6. Check voltage & waveform

7. Check individual components.

Observing the malfunction of different multifunction switch position can do much to identify a

problem. Detecting a problem in all circuits may indicate the problem in the power supply .

Switching to the external horizontal input (X-Y mode) disconnect the sweep and is a mean of

determining whether a problem is associated with the horizontal amplifier or sweep generator.At

the same time it indicate the condition of unblinking circuitry.

Varying the trigger source switch between internal & external triggering checks the trigger pivk

off circuitry. If the sweep is free run by adjusting the stability and trigger level control ,addition

circuitry may be checked .comparing operation in different trigger modes can often localize a

problem to specific trigger modes.

49

Vertical preamplifier plug in units are quick way of checking performance to the vertical

amplifier input .Once a problem is isolated to specific plug in unit ,plug in circuit board (if used)

may isolate the problem even further.

Once a problem has been traced to a specific block ,a close visual check may pin point the

problem .Troubleshooting job can be shortened by finding the burned components and loose

leads.

Another method of streamlining troubleshooting procedure is through the substitution

method.This method can be used in many levels of troubleshooting .In troubleshooting

instruments in plug in module isolate the faulty sub-system by substituting known good plug in

modules for those that are questionable.

There are some basic rules that we must remember & follow in using this method of

troubleshooting .

1. Ensure that we use the proper components ,by part number ,when substituting .

2. Ensure that power is removed when making the substitution ,to prevent damage to the

instruments.

3. Be careful when removing and replacing components to avoid physical /mechanical

damage to the components.

4. Keep the no. of components to be minimum ,substitute one components at one time.

5. Though several components in a circuit may have same part number ,avoid inter circuit

components swaps.Failure to return components to proper place whining a circuit may

require a complete calibration of circuit.If the components are placed properly ,circuit

may require only a performance check and spot calibration after the repair is competed .

6. Always return components to proper place after the problem has been solved.

50

51

Common Power Supply problem

1.Fuse blows when power is applied –shorted diode in bridge ,shorted filter cap.

2.Fuse blows after delay-overloaded output.

3.Excessive ripple –divide by 10 for approximate solid state value.

a.50 mv to 1.5 v-comparator ,speedup capacitor

b.1.5-8 V-output filter

c.8 V to more-input filter

4. off tolerance –Leaky speedup capacitor

5. Noisy output-poor connection,noisy diode ,noisy resistor

52

53

54

Conclusion:

55

Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:8

Aim

Handling of different types of multimeter: Frequency meters

Theory:

Digital frequency meter is a general purpose instrument that displays the frequency of a periodic

electrical signal to an accuracy of three decimal places. It counts the number events occurring

within the oscillations during a given interval of time. As the preset period gets completed, the

value in the counter display on the screen and the counter reset to zero. Various types of

instruments are available which operates at a fixed or variable frequency. But if any frequency

meter operates at a different frequency than specified range, it could carry out abnormally. For

measuring low frequencies, the deflection type meters are widely used. The deflection of the

pointer on the scale shows the change in frequency. The deflection type instruments are of two

types: one is electrically resonant circuits and other is ratio meter.

Operating Principle of Digital Frequency Meter

A frequency meter has a small device which converts the sinusoidal voltage of the frequency into

a train of unidirectional pulses. The frequency of input signal is the displayed count, averaged

over a suitable counting interval out of 0.1, 1.0, or 10 seconds. These three intervals repeat

themselves sequentially. As the ring counting units resets, these pulses pass through the time-

56

base-gate and then entered into the main gate, which opens for a certain period of time interval.

The time base gate prevents a divider pulse from opening the main gate during the display time

interval. The main gate acts as a switch when the gate is open, pulses are allowed to pass. When

the gate is closed, pulses are not allowed to pass that means the flow of pulses get obstructed.

The functioning of the gate is operated by the main-gate flip-flop. An electronic counter at the

gate output that counts the number of pulses passed through the gate while it was open. As the

next divider pulse is received at main gate flip-flop, the counting interval ends and divider pulses

are locked out. The resultant value displayed on a display screen which has the ring counting

units of scale-of-ten circuits and each unit is coupled to a numeric indicator, which provides the

digital display. As the reset pulse generator is triggered, ring counters get reset automatically and

the same procedure starts again.

The range of modern digital frequency meter is between the range from104 to 109 hertz. The

possibility of relative measurement error ranges between from 10-9 to 10-11 hertz and a sensitivity

of 10-2 volt.

Use of Digital Frequency Meter

For testing radio equipment

Measuring the temperature, pressure, and other physical values.

Measuring vibration, strain

Measuring transducers

Vacuum Tube Voltmeter (VTVM)

57

Theory

The voltmeter which uses the vacuum tube for amplifying the measurand AC and DC

voltage is known as the vacuum tube voltmeter (VTM). The vacuum tube increases the

sensitivity of the voltmeter because of which it can detect the signal of very weak strength.

The electronic voltmeter is used for measuring the voltage of direct, RMS and peak voltage

of the system. The vacuum tube has many advantages like they have high input impedance, wide

frequency range and high sensitivity.

The most significant advantage of the VTM is that it can draw very less current as compared

to the other meter. In VTM, the measuring signal is directly supplied to the vacuum tube of the

meter. The vacuum tube is amplifying the signal and pass it to the deflecting meter.

Types of Vacuum tube Voltmeter

The Vacuum Tube Voltmeter is classified into the following types.

1. Diode Type

o Peak Reading Diode Vacuum Tube Voltmeter

2. Single Triode

3. Balanced Triode Type

4. Rectifiers Amplifier Type

5. Amplifier Rectifier Type

Simple Diode Type Voltmeter

The circuit of the diode voltmeter consists the PMMC meter, load resistor, vacuum tube diode.

The vacuum tube diode connects in series with resistance raises the strength of the weak signal.

Because of the vacuum tube, the system becomes more sensitive than the normal voltmeter.

For obtaining the accurate reading from the voltmeter, it is essential that their current and

voltage are directly proportional to each other. This can be done by the help of the series

resistor. The circuit diagram of the diode vacuum tube voltmeter is shown in the figure below.

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The resistance of the series resistor is very high as compared to the resistance of the vacuum

tube diode. Thus the resistance of the tube is neglected. The linear relationship is obtained

between the voltage and current. The input supply deflects the pointer of the PMMC meter which

indicates the magnitude of the measured voltage.

In Diode vacuum voltmeter,

The value of the input resistance of the voltmeter is equal to the series resistance because high

voltage resistor decreases the sensitivity of the meter.

The frequency range of the diode voltmeter depends on the value of the series resistance. The

higher value of the series resistance decreases the frequency range of the meter.

The vacuum tube voltmeter is used in limited applications because of the low input resistance

and limited frequency range.

Peak Reading Diode Vacuum Tube Voltmeter

In this type of voltmeter, the capacitor is used in the circuit. When the capacitor is connected in

series with the resistance, then it is called the Series Type Peak Diode Reading Vacuum

Voltmeter, and in compensated shunt type voltmeter the capacitor is linked parallel with the

series resistor.

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The working of both the series and shunt type voltmeter is almost same. The capacitor becomes

charged by the positive peak voltage of the AC supply and its discharge through the shunt

resistor because of which their voltage decreases. The voltages rectify by the PMMC meter

connected in series with the resistor. The peak voltage is directly proportional to the rectifier

output voltage.

The vacuum tube voltmeter is used in the past for the measurement of voltages. Nowadays it is

replaced by the transistor voltmeter (TVM) and the field effect voltmeter (FETVM).

Transistor voltmeter

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FETVM-FET Voltmeter

This is a circuit of FETVM-FET Volmeter. The function of the VTVM is replaced by the FTEVM while at the same time ridding the usual line cord instrument. This circuit can allow a 0.5 volt scale range because drift rate of FETVM are superior to vacuum tube circuits. Here is the circuit:

The 2N4340 are implemented on this circuit because it has low noise and low leakage.

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v

Vacuum Tube Volt Meter (VTVM)

These types of instruments handle DC voltage, AC voltage, and resistance measurements. In this

type of voltage measuring device electronic amplifier is used in between the input and the meter.

Due to this arrangement the current drawn from the circuit under test is reduced. The range of

resistances used at the input side in range of 1-20 mega ohms. By these resistances variation we

can select the range to be measured. If this instrument uses the vacuum tube in the amplifier then

it is called as vacuum tube voltmeter. These are used in high power AC measurements. As the

invention of solid state devices used in the amplifiers, these type of voltmeters are called FET-

VM.

Conclusion:

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Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:9

Fault Location and repair of instruments – Multimeter

Aim: Transistor Circuit Test & Fault Finding using a Multimeter

Procedure for fault finding :

One of the main uses for multimeters whether they are analogue multimeters or digital

multimeters, DMMs is to test and fault find circuits like those in a transistor radio. Multimeters

are ideal items of test equipment for finding many faults in a transistor circuit.

However to use a multimeter to test a circuit and find faults it is necessary to have a little

knowledge about the circuit, and also to adopt a logical approach in tracking down any faults that

may exist.

The first step when looking at tracing any faults and testing a transistor circuit of any sort is to

look for the obvious or major faults. Fortunately most faults with electronics equipment such as

transistor radios are relatively major and therefore easy to find. Accordingly the first step in any

fault finding is to look for the major problems.

1.Check the supply to the circuit: The first steps in checking the circuit are to ensure that it

has power being supplied to it. This is easily done using a multimeter set to a voltage range.

Measure the voltage using a multimter at the points where the supply enters the circuit board. If

the multimeter indicates that there is no supply voltage then there can be a number of

possibilities to investigate.

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1.Battery could be flat if the equipment is battery powered

2.If the transistor equipment is battery powered, the battery could have been left in for many

months and corroded the battery compartment. Check for this and if there are signs of leakage

then clean and remove all signs of corrosion being careful not to touch any of the residue.

3.On-off switch faulty. This can be checked by disconnecting any power source and checking for

continuity across the switch

4.Corroded connector. One common problem is that connectors become corroded with time and

connections can become very poor, especially of the equipment has not been used for some time.

To overcome this it can help to unplug and then re-mate the connector.

5.Check for any broken wiring that would prevent the power reaching the circuit board

2.Check the outputs from the board: In the same way that broken connections may exist for

the power line, the same may be true of the outputs from the board. Again it is worth checking

any connectors that may have corroded or oxidised with time, and check for any broken

connections.

3.Check the inputs to the circuit: Likewise, if the signal inputs are not reaching the board then

it will not be able to perform. Again any switches, and connectors along with any broken wires

should be checked. Often a multimeter can be used to check the continuity of the wires, but first

ensure there is no power applied to the circuit.

By using a multimeter for the fault finding, it is possible to find many of the obvious faults that

can occur. If the problem cannot be found, and it appears that the correct power is reaching the

transistor circuit, and the inputs are all connected and present as well as the output lines being

intact, then further fault finding on the transistor circuit board itself may be needed. Again a

multimeter can assist in this.

Expected voltages in a transistor circuit

If all the inputs to the board appear to be correct, further tests can be undertaken using a

multimeter for the fault finding and to track down the problem. Again a systematic approach

should be adopted.

When testing a particular transistor circuit, a multimeter can be used to determine if the voltages

around the circuit are correct. To test and fault find a particular transistor circuit, it is necessary

to have an idea what the steady voltages should be. The circuit below is a typical basic transistor

circuit. Many circuits are similar to it, and it provides good starting point to explain some of the

points to note.

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The circuit shows several of the points where the voltage can be measured in a circuit. Most of

them are measured with respect to ground. This is the easiest way to make a voltage

measurement because the "common" or negative probe can be clipped to a suitable ground point

(many black probes used for the negative line have a crocodile or alligator clip for this purpose).

Then all the measurements can be made relative to ground.

There are normally a number of points around a transistor circuit that are easy to measure, and

the expected voltages can be anticipated for the most part if a few assumptions are made:

Assume the circuit is operating in a linear mode, i.e. it is not a switching circuit.

Assume the circuit is operating in a common emitter mode as shown in the diagram.

Assume the circuit has a resistive collector load.

If the assumptions above are true, then the following voltages can be expected. If not then

allowances need to be made for the changes.

1. The collector voltage should sit at approximately half the rail voltage. More specifically it

should sit at half the rail voltage less the emitter voltage. In this way the greatest voltage

swing can be obtained. If the transistor has an inductive load, as in the case of the intermediate

frequency amplifier in a radio which may have an IF transformer in the collector circuit, then

the collector should sit at virtually the same voltage as the rail voltage.

2. The emitter voltage should sit at around a volt or two. In most class A common emitter

circuits an emitter resistor is included to give some DC feedback. The voltage across this

resistor is typically a volt or so.

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3. The base voltage should sit at the PN junction turn on voltage above the emitter. For a silicon

transistor, which is the most common type, this is around 0.6 volts.

Indications of the types of voltage expected can be seen on the circuit diagram.

In addition to this, there are many other types of circuit which may need fault finding. Switching

circuits are quite common these days where transistors are used to drive other elements such as

relays or other devices. These do not operate in a linear mode. Instead all voltages are either on

or off. The collector voltage will either be approximately zero when the transistor is on, and

approximately the rail voltage when off. The emitter will usually be connected to ground, and the

base voltage will be high, i.e. approximately 0.6 volts for a silicon transistor when the transistor

is on (i.e. collector near zero), and low, (zero volts) when the transistor is off and the collector is

high.

Conclusion:

A multimeter is an ideal piece of test equipment to help with fault finding an electronics

transistor circuit. Often circuits like transistor radios fail after they have been used for many

years, and it is useful to be able to mend them Also when constructing equipment, circuits do not

always work first time and it is necessary to fault-find these circuits. While it will not be possible

to solve all problems using a multimeter, it is one of the most useful basic tools for any fault

finding job.

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Government Polytechnic, Muzaffarpur

ELECTRONIC CONSTRUCTION AND REPAIR LAB

Subject Code: 1620407

Experiment:10

Aim: Repair of faulty study panels of your laboratory

Theory: A work area of a electronics laboratory should consist of a large workbench, desk,

or table (preferably wooden) for performing circuit assembly, with household electrical power

(120 volts AC) readily accessible to power soldering equipment, power supplies, and any test

equipment. Inexpensive desks intended for computer use function very well for this purpose.

Avoid a metal-surface desk, as the electrical conductivity of a metal surface creates both a

shock hazard and the very distinct possibility of unintentional “short circuits” developing from

circuit components touching the metal tabletop. Vinyl and plastic bench surfaces are to be

avoided for their ability to generate and store large static-electric charges, which may damage

sensitive electronic components. Also, these materials melt easily when exposed to hot

soldering irons and molten solder droplets.The electronics workbench consists of an electric

panel with protected sockets and different voltage outputs, in order to make the work to

electronics circuits very easy and comfortable. The electric panel consists of 3 surface

mounting distribution boards (gewiss), the size of each one is 12 slots. The first one on the left

is equipped by a circuit breaker (which protects everything from short circuits, overloads and

current leakages); 3 switches that pilot 2 transformers + 2 power supplies located in the

junction box on the left; and a kill switch. If it's pressed, it simulates a current leakage that

make the circuit breaker turn off. The second one is equipped by 4 schuko sockets, whereas in

the third one we can find the outputs of the transformers/power supplies, like the 230V

insulated socket, the 12/24V alternating current outputs and the 5V/12V direct current outputs.

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Apparatus:

Digital multimeter

Wire stripping pliers

Jumper wires

Needle-nose pliers

Screwdrivers

Soldering iron and solder (“rosin core”)

Soldering gun

Utility knife

Slip-joint pliers

Adjustable-joint pliers

Procedure:

Repair of circuit breaker:

Reset circuit breaker: We need to turn the switch off first and then move it back into the

"On" position. The circuit breaker generally turns off when a circuit has overloaded or short

circuited. Check for loose wires: Often problems such as flickering of lights are caused due to faulty

wiring. Check for any loose wires and replace them. Check the load: In case of a circuit overload, before resetting the circuit breaker, check all

appliances connected into the circuit. If there are too many, shift some to another circuit.

To Replace:

1. Remove fuse or trip circuit breaker to off for the lab or outlet you are replacing.

Test to be sure we have correct circuit by plugging a lamp that we know works into

the receptacle.

2. Unscrew and remove face the plate.

3. Unscrew the mounting screws at top and bottom and pull the unit out.

4. Notice how wires are connected and connect them to the new unit the same way.

All white wires are connected to the side with a silvery color and the black wires to the

brassy terminals.

5. A green grounding wire is connected on newer systems so be sure to reconnect

this wire also. If not and a loose ground wire is present, connect it to the grounding

screw attached to the top of the metal support plate.

6. Reassemble the outlet doing steps above in reverse order.

7. Wrap electrical tape around the entire top, bottom and sides of the outlet so that

when removing it in the future, we have less of a chance of touching wires.

If one of sockets has been scorched, it's usually been caused by overloading or loose

connections in a plug. Don't plug circuit back in without dealing with the problem first or it will

happen again.

1. Safety first

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Never take risks with electrical safety. Modifications to any circuit must comply with the latest IEE Wiring Regulations. New or replacement cables or sockets may need RCD protection.

Zoom: [i mage descripti on]

Step 1

Start by isolating the circuit. Use a socket tester to double-check that it's dead. Unscrew the socket faceplate and pull it away from the wall, but keep the screws in case the new ones don't fit.

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Step 2

Loosen the terminal screws and free the cable cores. If the insulation has been heat damaged, cut back the cores and strip the ends. Run green/yellow sleeving over the earth core if it's exposed. As the metal back boxes must be earthed, run a short length of earth cable between the earth terminals of the back box and the faceplate.

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Step 3

Connect the live core or cores to the live terminal (L) of the new faceplate, the neutral to the neutral terminal (N) and the earth to the earth terminal (E or (Earth symbol)). Fully tighten the terminal screws, and fit the new faceplate. If the new screws don't fit the lugs of the old box, just re-use the original screws. Finally, use the socket tester to check you've wired everything correctly.

Precaution:

Use electrical cords only if they are in good condition. Cords must not be cracked, frayed, or

have corroded prongs.

Do not use 3-to-2 prong adapters unless other grounding provisions have been made. Plug 3-

prong plugs into 3-prong outlets.

Use power strips that have circuit breakers or fuses. Do not link power strips in series.

Do not leave cables and cords unsecured and hanging in areas where they can pose a trip and

movement hazard. Place cords so that they are not subjected to mechanical stress or

temperatures that could damage the insulation.

Do not conceal cords behind or attach electrical cords to building surfaces.

Do not leave electrical circuits exposed. Use electrical tape to insulate wires or use a guard as

cover to prevent accidental contact.

Do not block access to electrical panels.

Do not install standard electrical equipment in locations where flammable gases, vapors,

dusts, or other easily ignitable materials are present. If electrical equipment is used in a

chemical fume hood, elevate it to allow efficient air flow.