Output at Ais checked.if alright, the stages from microphone to IV stage are correct.the output B is checked. If ,no output either the V or the VI stage may be defective. Then , output at C is checked which will finally decide whether the stage V is defective or the VI .
Trouble shooting in divergent circuits is done by isolation technique.
IDENTIFYING THE FAULTY STAGE,Audio & video system
AUDIO & VIDEO System
IDENTIFYING THE FAULTY STAGE
PRANAV VEERANI (130280111117)
Submitted to :
PROFESSOR PRATIK GIRI GOSWAMI
IDENTIFYING THE FAULTY STAGE
Stages are connected in four types of
4.Closed loop(feedback) circuits
There are three method of this stage .
Stages are in series one after the other.
1.Signal Injection & Tracing
3.Short circuiting the input
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).
In sequential circuit , the quickest method of
finding out which stage is faulty is split half
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:
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.( )
Several loudspeakers connected to one
output of final power amplifier stage.(1)
Switching circuit with one input and several
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)
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)
• 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
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.
Feedback circuits from a closed loop.
Servo controlled devices(2)
Automatic gain control(4)
• 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
Some common faults:
Capacitor(open , short , leaky)
Inductor(open , short)
Diode(open , short)
Transistor(open , short , leaky)
Common faults in PCB:
1.Solder bridge between adjacent tracks
3.Break in plated through hole(PTH)
4.Loose connection in connectors
5.Dry or cold solder joint
AUDIO AND VIDEO ENGINEERING
R G GUPTA