AUDIO & VIDEO SystemIDENTIFYING THE FAULTY STAGE

Presented by:PRANAV VEERANI (130280111117)

Submitted to :PROFESSOR PRATIK GIRI GOSWAMI

IDENTIFYING THE FAULTY STAGE

Stages are connected in four types of circuit configurations:

1.Sequential stages 2.Divergent circuits 3.Convergent circuits 4.Closed loop(feedback) circuits

SEQUENTIAL STAGES

There are three method of this stage . Stages are in series one after the other. 1.Signal Injection & Tracing 2.Signal substitution 3.Short circuiting the input

SEQUENTIAL STAGES

1.Signal injection & tracing : In this method signal is injected at the input of the system & its presence is detected by signal tracer at different stages. Signal tracing can be done by a diode tracer, or a cathode ray oscilloscope(CRO).

2.Signal substitution : In this method , Signal is given at the inputs of different stages & the final output is checked.

3.Short circuiting the inputs : One by one for locating the source of noise(like self oscillations).

SEQUENTIAL STAGES In sequential circuit , the quickest method of finding

out which stage is faulty is split half method .Split Half Method : In this method , the output at a

stage in the middle of the sequential stages is checked. If it is correct, the first half of the stages is alright & the defect lies in the second half. Then, the output at the middle stage of the second half is checked to find out which portion is defective & so on ,until we reach at the correct stage . Figure of this method is shown below:

SEQUENTIAL STAGES

Split Half Method

DIVERGENT CIRCUITS

The circuit which has one input path , but the

output takes several paths is called divergent circuit. One such circuit of power supply output , which sends power to several stages from its output point.( )

DIVERGENT CIRCUITS

Several loudspeakers connected to one output of final power amplifier stage.(1)

Switching circuit with one input and several output.(2)

DE multiplexer circuit which receives one input but gives several outputs.(3)

Video detector input is one but there are several outputs, like sound section, luminance , chroma and raster sections.(4)

DIVERGENT CIRCUITS

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CONVERGENT CIRCUITS

The circuit which has several input but only

one output is called convergent circuit.Mixer stage for microphone in the PA system

in which several microphone are connected in the input and there is only one output for feeding to the amplifier(1)

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CONVERGENT CIRCUITS

• Multiplexer which takes several signals in its input and gives out only one signal.(2)

• Logic gates(except NOT gate) which give one output for two or more input.(3)

• Switching circuit with several inputs and one output.(4)

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CONVERGENT CIRCUITS

Fault diagnosis in convergent circuits will also be done in the same way as in divergent circuits . Each input circuit will be isolated to find the output . If expected output is obtained after isolating a circuit in the input, than that circuit is faulty.

CLOSED LOOPCIRCUITS

Feedback circuits from a closed loop.Negative feedback(1)Servo controlled devices(2)Positive feedback(3)Automatic gain control(4)

CLOSED LOOPCIRCUITS

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FAULTY COMPONENT• Faulty component in the Faulty Stage: 1.Measurement of resistance, dc voltage and ac signal voltage at

the specified test points. 2.Substitution of the suspected component by a good one. Passive and active components may become open or leaky or

short. The causes for components to become faulty are many . But voltage fluctuation, transients , dust , temperature variation , grease between tracks of PCB, dry or cold solder joints, vibrations/shocks, mishandling , expiry of life ,etc. are the most common causes for failures.

Dust is the biggest enemy of an electronic equipment because it prevents radiation of heat from the ICs and other components.

FAULTY COMPONENT

Some common faults:Resistor(open)Capacitor(open , short , leaky)Inductor(open , short)Transformer(leaky)Diode(open , short)Transistor(open , short , leaky)

FAULTY COMPONENT

Common faults in PCB: 1.Solder bridge between adjacent tracks 2.Pin holes 3.Break in plated through hole(PTH) 4.Loose connection in connectors 5.Dry or cold solder joint

REFERENCE

AUDIO AND VIDEO ENGINEERING SYSTEMS BY R G GUPTA

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