The method of observing the shape, amplitude, period, etc. of each test point waveform when the circuit under test is operated in the AC state through an oscilloscope to determine whether the components in the AC circuit are damaged or deteriorated is called a waveform observation method, which is simply referred to as a waveform method.
If the fault is not determined by the intuitive method and the multimeter measurement method, the waveform method can be used to understand the problem. The waveform method can check whether the dynamic function of the circuit is normal. The detection result is more reliable than the former two methods, and the waveforms of each point are often given in many electrical product specifications or maintenance data, so the waveform method is one of the commonly used fault detection methods. .
When the waveform circuit is used to detect the oscillation circuit and the signal generation circuit, no other signals need to be added, and when detecting other circuits such as amplification, shaping, frequency conversion, detection, rectification, etc., the standard signal of the signal source needs to be fed to the input terminal.
1) Method 1 Using an oscilloscope, starting from the first stage of the appliance to be repaired, sequentially shifting to the rear unit circuit to observe whether the signal waveform is normal. If the stage circuit has no output waveform or the waveform is distorted, it can be determined. The fault is at this level. For complex multi-level circuits, segmentation detection can be used to narrow the test range and speed up the inspection.
2 When using an oscilloscope to observe the input and output signal waveforms of a questionable circuit, if there is an input signal and no output signal or signal waveform is distorted, the problem exists in the circuit under test.
2) Note 1 The oscilloscope with appropriate bandwidth and sensitivity should be selected. It is best to use an oscilloscope with quantitative test function, that is, an oscilloscope with calibration amplification sensitivity, scanning speed, comparison voltage and time-scale signal.
2 Should pay attention to the influence of the oscilloscope input impedance on the circuit under test, if necessary, use a 10:1 fixed attenuation probe for detection.
3 should pay attention to the influence of the DC voltage in the circuit under test on the input device of the oscilloscope. Let UD be the DC voltage value, Us be the signal voltage, Umax is the maximum signal voltage that the oscilloscope can observe, then Umax≥UD + Us should be satisfied, otherwise the method of series capacitor (straight) should be used.
When using the waveform method to detect complex circuits, it is important to know the input and output waveforms or related node waveforms of each part of the circuit during normal operation. The maintenance personnel should pay attention to collecting relevant information or conducting test records, and record and check.
Silicon TVS / TSS:
Diode TVS (Transient Voltage Suppressor), also known as Transient suppression diodes, is widely used a new type of high efficient circuit protection device, it has a fast response time (the nanosecond) and high surge absorbing ability.When it ends of stand moments of high energy shock, TVS can bring the two ends at high rate from high impedance to a low impedance between impedance values, to absorb a large current moment, put it at both ends of the voltage restraint on a predetermined value, thus protecting the back of the circuit components are not affected by the impact of the transient high pressure spikes.
Silicon TVS Transient Voltage Suppresso,Silicon TSS Transient Voltage Suppresso
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