First, direct observation
The so-called direct observation method refers to the method of directly observing the surface of the circuit to be inspected to find the problem and looking for the fault without any means of equipment. Generally, it is divided into two types: static observation and power-on inspection. The static observation includes the following aspects. .
1. Observe whether there is a burnt mark on the surface of the printed circuit board and components, whether the connection and components are detached or broken.
2. Observe the use of the instrument. Whether the instrument type selection is appropriate, whether the function and range selection are correct, and whether the common connection is handled properly. It is preferred to exclude external faults and then observe the circuit itself.
3. Observe the power supply of the circuit. Whether the voltage value and polarity of the power supply meet the requirements, whether the power supply has been properly connected to the circuit, etc.
4. Observe the installation of components. The polarity of the electrolytic capacitor, the lead terminals of the diode and the triode, the lead terminals of the integrated circuit, whether there is a connection error, a missed connection, a mutual contact, etc., whether the installation position is reasonable, whether there is shielding means for the disturbance source, and the like.
5. Observe the wiring situation. Input and output lines, strong and weak points, AC and DC lines, etc. violate wiring principles.
A power check can be performed after static observation. After the power is turned on, observe whether the components are hot or smoked, and the transformer has no burnt smell or fever and abnormal sound.
The direct observation method is suitable for preliminary inspection of faults, and some more detailed faults can be found.
Second, the instrument test method
1, power failure test method
It is a method of judging the fault by measuring the resistance value of the circuit or component with the multimeter ohmmeter under the condition that the circuit is powered off. For example, check whether the wiring, solder joints and fuses in the circuit are open, measure the resistance value, capacitor leakage, on/off of the inductor, and check the quality of the semiconductor device. During testing, in order to avoid the influence of the relevant branch, one end of the component under test should be disconnected from the circuit. At the same time, in order to protect the components, do not use high blocking and low blocking to prevent high voltage or large current from damaging the semiconductor in the circuit. The PN junction of the device.
2, live test method
It is a method of measuring the static voltage value or voltage waveform of each point in the circuit by means of an instrument under the condition of charged circuit, and conducting theoretical analysis to find the location of the fault. For example, check whether the static working point of the transistor is normal, whether the static parameters of the integrated device meet the requirements, and whether the logical relationship of the digital circuit is correct.
3. Signal tracing method
According to the need to add a signal that meets the requirements at the input of the circuit, according to the flow of the signal from the previous stage to the latter stage, use an oscilloscope or a voltmeter to check the transmission of the signal in each part of the circuit, and analyze the function of ID Anlu. Whether it is normal, so as to determine the location of the fault. This method should normally be used under normal conditions where the circuit's quiescent operating point is normal.
4, split test method
For some loop circuits with feedback, their working conditions at different levels are involved. In this case, the method of splitting the loop can be used to remove the feedback loop and then check it step by step, so that the fault location can be detected more quickly. The phenomenon of self-oscillation can also be checked by this method.
5, comparison method
When you suspect that there is a problem with a certain circuit, you can find a normal circuit for comparison. Compare the status and parameters of the two items one by one. You can quickly find the abnormal parameters in the circuit, and then analyze the cause of the fault and find it. To the point of failure.
6, the alternative method
Sometimes the fault is hidden and cannot be found quickly. Further inspection is needed. At this time, the unit circuit or component that has been debugged can be used instead of the unit circuit in question to judge whether it is in the unit circuit. After the problematic unit circuit is determined, a partial replacement method can also be used in the unit circuit to replace the suspected component with a well-confirmed component, gradually narrowing the suspected range of the fault, and finally finding the fault point.
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