Audio Repair

8/13/2019 Audio Repair

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Audio System General Trouble Shooting

Nevertheless, audio systems are less used now-a-days due to “many-

in-one” technology like DVD players, which can play back audio as

well as video. But, In order to have an advanced acoustic effect,

people use home theatres. It also work in similar manner to any other

audio systems as previous were. The main logic behind any audiosystem is to amplify the audio coming from the source and also

providing option to select the required frequencies like bass and treble

as they require.

The audio sources are may be cassettes in case of tape recorder, the

areal wire in case of radio; similarly, output of one audio system can

be the input for many other audio systems. In case of home theatres

the audio output taken from the DVD players or any other resources

will be feed in to the input point of the audio systems. Then it will be

/omtingel and done quality optimization in order to get good musicquality . Like any other electronic circuit it also will be having power

supply section and the remaining section will be related to the process

of amplification and purification of the signal .

Let us take a case study for which I received a home theatre system for

the service. This one is from the ‘Mercury’ company. The problem

was no sound output. The system was getting switched ON. It was

producing an ultimate quality of sound when it was working properly.


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Picture showing the Audio Unit

I just removed back cover of the audio system

Picture showing details of the Audio Unit


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Click Here

/

Picture showing the interior of the system

You can also observe the quality of the unit is good from the size of

the transformer and also with the size of heat sink provided to the ICs

of the circuit from the below picture.

Picture showing the Transformer and the HeatSink

Also I removed the front cover of the system; there was also a small

circuit inside which is nothing but the radio circuit (shown in below

circuit).


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Picture showing the Radio Circuit in the system

The amplifier circuit (please do not get confused with radio circuit

which is another one) is designed using three ICs. One IC for the pre-amplification and other two ICs for the final amplification of left side

and right side speaker out lets. For more clarification please see the

below picture

4

Picture showing the audio circuit and components

I would like to suggest any service engineer, to give careful

observation to the circuit board before actually starting the repair work


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on it. As I observed, the board carefully, I found a resistor with

burning symptoms (it is also highlighted in the above picture).When I

made trace on the back, I found the resistor is the one through which

power was flowing to TDA 2030 amplifier ICs.

Picture showing the Audio Circuitry

One key point I would like to share with the readers is, in any circuit,

whether it is TV or other board, if any resistor bringing voltage to any

IC is burnt or opened, then we should not simply replace the resistor.

The main cause will be the shorted IC or any other component related

to the IC. For example, if a vertical IC of TV is shorted then definitelythe IC and the resistor from which the current is flowing to the IC will

be getting heated.

In the same way, in the above circuit the main culprit was the IC.

When I switched on the set, the system was getting switched on

properly. So, I did not concentrated on the power supply section.

I just replaced two (both left and right) IC TDA 2030.and also for the

safer side to promise the original condition, I also replaced the pre-

amplifier IC TDA 2030 and also the resistor.

Then I just connected two speakers and switched on the set, tuned theradio frequency to the local station, it reproduced a heaven feeling of

super music.

This was a case study. But, problem of different kinds will appear in

different cases.

The general tips I want to share with you are as follows.

1) Don’t attempt any kind of service when you are in hurry and

restless.


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2) Don’t work under pressure.

3) Please make sure that, you have kept all the necessary tools near by

you before starting the service work.

4) If you have circuit diagram and the IC details of the circuit with

you, please refer first before staring any service.

5) After opening the system, carefully at least for five minutes search

thoroughly for any dry joints, loose connections, burnt components,

bulged capacitors.

6) Also keep in mind that, most sensitive components in any

electronic circuit are the semiconductor components like Transistors,

ICs, Diodes and if used fuse and fusible resistor.

7) In any audio systems, if the audio level is fluctuating then just try by replacing the volume control, also you can put 3-4 drops of petrol

in to volume control and make it correct.

Picture showing the Controls of the circuit

8)Most of the time the loose contact inside the selector switch (if used)will be the main faulty component in the circuit. Above method can be

used to correct the selector switch.

9) At any cost do not ‘turn’ the IFT coils in the circuit.

10) Before removing the connectors of the circuit please note it on the

book how to reconnect.


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Picture showing the connector of the Transformer

11) Don’t hesitate to ask any senior about the doubts you are having.

12) Whenever a senior starts working on the circuit board, keenly

observe him what he does, how he trouble shoots. Also learn the

techniques which you found useful.

13) In order to get the good results always put good quality

components.

14) While replacing the speakers of any audio systems please get good

quality speakers.

Picture showing the speaker


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15) For the problem of distorted sound, please look for the dry joints

and the loose connections. Also try by cleaning the selector switch as

well as volume controls.

16) For humming sound in the system, the main reason will be

improper grounding of the system metallic body. Connect the metallic

body of the system to the negative of the circuit board. Also, the badfilter capacitor of the power supply section will be the main reason for

the humming sound.

Details of the TDA 2030

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Audio Repair