Electronic test items: 8 methods of circuit fault analysis

Date：2022-03-01 18:08:00Views：874

In addition to rich theoretical knowledge and practical operation, the troubleshooting method of electronic circuit fault is also very important. A good method can get twice the result with half the effort. So how should the electronic circuit troubleshoot? Generally, it can be detected by input to input sequence or by the reverse method from output to input. No matter from which direction, electronic circuit fault detection can generally be judged by the following eight methods.

1、 Direct observation

In case of circuit failure, usually the instrument will not be used for measurement immediately, but the visual observation is used to find the possible abnormal parts of the circuit. The direct observation method is divided into no power and power on detection.

Power failure detection is to check whether the grade and polarity of power supply voltage meet the circuit requirements; Whether the polarity of electrolytic capacitor and the pin position of diode and triode and the pin position of integrated circuit have problems such as false soldering, wrong soldering and crossing; Whether the wiring is unreasonable; Whether the circuit of the printing plate is broken when printing; The resistance and capacitance are obviously burnt.

The power on inspection is mainly to observe whether the components have overheating, smoke and obvious burning smell, and whether the filament of electronic tube and oscilloscope tube has high-voltage ignition and other problems.

2、 Multimeter detection

Multimeter detection is mainly to check the static working point, in which the resistance value and DC working state in the power supply system, triode, integrated block and circuit of electronic circuit can be detected by multimeter. Check to see if the value is normal.

3、 Signal tracing method

In a complex circuit, you can access a signal at the input end, and then observe the waveform and amplitude change from the front stage to the rear stage or from the rear stage to the front stage through the oscilloscope, and finally check which stage is abnormal.

4、 Comparison method

The comparison method is more intuitive. It mainly compares the parameters of the suspected fault circuit with the same circuit in normal working state, finds out whether there is a value with large parameter difference, and then analyzes the fault cause to determine the fault location.

5、 Substitution method

For the electronic circuit whose fault is not obvious, when it is unable to make intuitive judgment or suspected fault point, the existing same components can be used for replacement. By replacing and observing whether the circuit changes, the fault judgment orientation can be shortened.

6、 Bypass inspection method

If there is parasitic oscillation in the circuit, the capacitor with a certain capacity can be used to bridge the capacitor between the place to be checked or the reference grounding point, and then observe whether the oscillation exists. If the oscillation disappears, it indicates that the oscillation is generated in the previous circuit or the circuit near it. If not, move back and continue to look for checkpoints. When selecting capacitors, it should be noted that the bypass capacitance should not be too large and can better eliminate adverse signals.

7、 Short circuit inspection method

The short circuit inspection method is that we actively create a temporary short circuit to short circuit some circuits. As for the amplification circuit shown in the figure above, the collector to ground voltage of T2 measured by multimeter is 0. Then we suspect that there is an open circuit in L1 circuit, and then create a temporary short circuit at both ends of L1. At this time, if the value of vc2 is normal, it indicates that the fault is on L1.

It should be noted that the short-circuit method can not be used in the power circuit. Remember.

8、 Open circuit inspection method

The short circuit method mentioned above is the most effective to check the open circuit. Similarly, the short circuit method is also the most effective. The thinking of open circuit inspection method is similar to the previous methods, which is used to eliminate doubts and shorten the scope. Assuming that the regulated power supply is connected to a faulty circuit, and the output circuit is too large at this time, if we disconnect some branches of the circuit in turn, and then observe the current output of the circuit, so as to judge the branch of the fault.

The operation efficiency of the whole system depends on the safety of electronic circuit operation. Therefore, the diagnosis of electronic circuit faults is conducive to improve the stability of the equipment. There are many ways to judge faults, which can be flexibly applied through different instruments and equipment, so it will be easier to judge complex faults. It's no exaggeration to say that as long as you master one or two of them and have the experience of repairing circuits, you can be handy.