The Most Complete Circuit Test Process (2)

Other Work in Electronic Circuit Debugging

1. Determine the test points: According to the working principle of the system to be adjusted, formulate the debugging steps and measurement methods, determine the test points, mark the positions on the drawings and the PCB board, and make debugging data record form, etc.

2. Set up a debugging workbench: The workbench is equipped with the necessary debugging instruments, and the equipment should be easy to operate and easy to observe. Special reminder: When making and debugging, be sure to arrange the workbench clean and tidy.

3. Select the measuring instrument: For the hardware circuit, the measuring instrument should be selected by the system to be adjusted, and the accuracy of the measuring instrument should be better than that of the system under test; for software debugging, it should be equipped with a microcomputer and a development device.

4. Debugging sequence: The debugging sequence of the electronic circuit is generally carried out according to the signal flow direction, and the circuit output signal that has been debugged before is used as the input signal of the next stage to create conditions for the final unified adjustment.

5. Overall debugging: When selecting a digital circuit implemented by a programmable logic device, the input, debugging and downloading of the source file of the programmable logic device should be completed, and the programmable logic device and the analog circuit should be connected into a system for overall debugging and result testing.

Matters Needing Attention in Circuit Debugging

Whether the debugging result is correct is largely affected by the correctness of the test quantity and the test accuracy. In order to ensure the test results, the test error must be reduced and the test accuracy must be improved. For this reason, the following points should be paid attention to:

1. Use the ground terminal of the test instrument correctly. Use the electronic instrument with the ground end connected to the chassis for testing. The ground end together should be connected with the ground end of the amplifier. Otherwise, the interference introduced by the instrument chassis will not only change the working state of the amplifier, but also cause errors in the test results. According to this principle, when debugging the emitter bias circuit, if Vce needs to be tested, the two ends of the instrument should not be directly connected to the collector and the emitter, but Vc and Ve should be measured to the ground respectively, and then subtract the two. If a multimeter powered by a dry battery is used for testing, since the two input terminals of the meter are floating, it is allowed to directly bridge between the test points.

2. The input impedance of the instrument used to measure the voltage must be much larger than the equivalent impedance of the measured place. If the input impedance of the test instrument is small, it will cause shunt during measurement, which will bring great error to the test result.

3. The bandwidth of the test instrument must be greater than the bandwidth of the circuit under test.

4. Correctly select the test point. When the same test instrument is used for measurement, the measurement points are different, and the error caused by the internal resistance of the instrument will be very different.

5. The measurement method should be convenient and feasible. When it is necessary to measure the current of a circuit, it is generally possible to measure the voltage but not the current, because the circuit does not need to be changed to measure the voltage. If you need to know the current value of a branch, you can get it by measuring the voltage across the resistor on the branch and converting it.

6. During the debugging process, not only we must observe and measure carefully, but also be good at recording. The recorded contents include experimental conditions, observed phenomena, measured data, waveforms, and phase relationships. Only a large number of reliable experimental records are compared with the theoretical results, the problems of circuit design can be found and the design scheme can be improved.

Troubleshoot During Debugging

It is necessary to carefully find the cause of the failure, and do not remove the line and reinstall it if the failure cannot be solved. Because if it is a problem in principle, even reinstalling it will not solve the problem.

1. General method of fault inspection
For a complex system, it is not easy to accurately find faults in a large number of components and circuits. The general fault diagnosis process starts from the fault phenomenon, makes analysis and judgment through repeated tests, and gradually finds out the fault.

2. Fault phenomenon and cause of failure
Common fault phenomenon: The amplifier circuit has no input signal, but has an output waveform. The amplifier circuit has an input signal, but no output waveform, or the waveform is abnormal. The series regulated power supply has no voltage output, or the output voltage is too high and cannot be adjusted, or the output voltage regulation performance is deteriorated, and the output voltage is unstable. Oscillation circuit does not produce oscillation, counter waveform is unstable and so on.

The reason for the failure: The fixed product fails after a period of use, which may be due to damage to the components, short-circuit and open-circuit of the connection, or changes in conditions, etc.