Hello friends, I hope you all are doing great. In today’s tutorial, we will have a look at How to Troubleshoot Power Amplifiers. Troubleshooting is process to solve the problem is used to repair damage different instruments, machines or circuits. In the previous tutorial, we have discussed different amplifiers such as class A, Class B, and Class C power amplifiers.

In today’s post, we will have a detailed look at the troubleshooting and reparing of power amplifiers. We will perform troubleshooting for class A and class AB amplifier. So let’s get started with How to Troubleshoot Power Amplifiers.

How to Troubleshoot Power Amplifiers

First of all, we discuss troubleshooting of class A amplifier.

Class A Amplifier Troubleshooting

The proper working-class amplifier is shown in the below figure where a fine sine wave is generated when the input voltage is applied.

Let’s take 4 faulty signal output waves which are normally occurred.
In figure denoted as ‘a’ oscilloscope shows a dc level equal to the dc source voltage denoting that transistor is the cutoff mode.
The 2 main reasons for this condition are given as.
- The PN junction of the transistor is open.
- Resistance R4 of the circuit is open and stops current from collector and emitter.
In figure denoted as ‘b’ the oscilloscope shows a dc signal at collector almost equal to the voltage of emitter.
The main reasons for this state are given as.
- The transistor is a short circuit with transistors.
- Resistance R2 is an open circuit that caused transistor to be in the saturation region.

In 2nd condition, enough high input signal can cause saturation at the negative peak which causes short pulses at the output.
In figure denoted as ‘c’ oscilloscope display that an output signal which shows that the transistor is in cutoff for a small part of the input signal.
The 2 main reasons for this are.
- The position of Q point has changed down due to high variations in the tolerances of resistance.
- Resistance R1 is an open circuit biased transistor in the cutoff region.
The figure denoted showed that the input wave is enough to cause a cutoff region for a small part of the signal.
In figure denoted as d oscilloscope show an output signal which shows that the transistor is in saturation by letting a small part of the signal.
The reasons for this are.
- Faulty value resistance has changed the position of Q-point towards saturation.
- Resistance R2 is an open circuit that causes the transistor to be in saturation region and the input wave brought out saturation for a small part of the signal.

Class AB Troubleshooting

In the below figure class AB push-pull amplifier is shown the output of ac signal is also shown correspondent to an ac input signal.

The 2 faulty output signal is shown in the below figure.
The figure denoted as a show that only positive half of the input wave is exits at the output.
- Then the first main reason is that diode Di is open. If it is error the positive half of the input wave is forward biases the diode D2 and cause transistor Q2 to operate.
- The second possible cause is that the base-emitter junction of transistor Q2 is open so a positive half cycle of input signal exits on the output as transistor Q1 is operating.
The waveform shown in figure b indicates that only negative half of wave is exist at the output.

- The first fault for this is that diode D2 is an open circuit. If this is error negative half of input wave forward biases diode D1 and put the half signal at the base of transistor Q1.
- The second fault is that the base-emitter junction of transistor Q1 is open due to that negative half of the input wave display at the output since transistor Q2 is operating.