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Amplifier troubleshooting skills
We have talked about the basics of an amplifier and types of amplifiers in other articles in this channel. Now we will proceed to take a look at the steps which are necessary and the equipment required to fix the fault and help you troubleshoot an amplifier which is not performing upto the mark. So here you go as follows.
To debug an amplifier for fault we need two things:
Choosing test equipment & Amplifier troubleshooting procedure
Choosing test equipment
Selection of test equipment depends on the application for which an amplifier is being used.
If we are mainly concern with the input and the amplified output voltage, and distortion in signal is not our concern then multimeter is a decent choice.
If the amplifier belong to an area where distortion, and noise count e.g. CD player, Computer monitor etc, then for debugging scope can be used. They also allow you to observe input and output signal at same time.
To troubleshoot a Hi-Fi stereo audio system distortion meter will be required. This will help you to monitor the amount of noise and harmonics associated with audio signal.
Frequency response should be check where frequency is also our concern, like in case of frequency modulation and demodulation.
Troubleshooting guide step by step
Check the DC biasing voltage i.e. VBE and VCE.If these voltages differ from nominal value then possible causes are:
Wire routing problem
Short or an open capacitor
Short across bypass and decoupling capacitor, causing to shift the DC level.
If Biasing dc voltage is OK then consider the circuit for ac operation.
If ac source is present but no voltage is appearing at base of transistor, then possibly an open path between source and base. This could be due to open coupling capacitor.
If the output of ac source Vo is missing then it is possibly due to open output coupling capacitor.
Check for ac voltage on emitter w.r.t ground. Use oscilloscope to monitor the signal. The reason is that scope also shows signal distortion. If there is any voltage, it means bypass capacitor that ground the ac signal is not working. This create voltage across Re,which appear as emitter voltage.
Some time in an audio system we hear hum and noise. This is due to electromagnetic interference that induces a noise spike that travel to base, there by amplify itself and appear as an unwanted signal at the output of amplifier. This noise may also due to noise in power supply. It means that a filter capacitor of power source is malfunctioning.