Methods for troubleshooting with a digital multimeter
A digital multimeter (DMM) is a measuring instrument that uses the analogue/digital conversion principle to convert a measurement into a digital quantity and display the measurement result in digital form. Compared with the pointer multimeter, digital multimeter has the advantages of high accuracy, fast speed, large input impedance, digital display, accurate reading, strong anti-interference ability, high degree of measurement automation and is widely used. However, if not used properly, it is easy to cause failure.
Digital multimeter troubleshooting should generally start from the power supply. For example, after turning on the power supply, if the LCD yuan display, you should first check whether the voltage of the 9V laminated battery is too low; whether the battery lead is disconnected. Looking for faults should follow the "first inside and outside, first easy after the difficult" order. Digital multimeter troubleshooting can be carried out in the following way.
First, appearance check.
You can touch the battery, resistor, transistor, integrated block temperature rise is too high. If the newly loaded battery is hot, the circuit may be shorted. In addition, it should also observe whether the circuit is broken, desoldering, mechanical damage and so on.
Second, detect the working voltage at all levels.
Detect the operating voltage at various points, and compare with the normal value, first of all, the accuracy of the reference voltage should be ensured, it is good to use a piece of the same model or similar digital multimeter for measurement and comparison.
Third, waveform analysis.
With an electronic oscilloscope to observe the circuit voltage waveforms at various key points, amplitude, period (frequency), etc.. For example, such as measuring whether the clock oscillator vibration, oscillation frequency is 40 kHz. if the oscillator has no output, indicating that the TSC7106 internal inverter is damaged, it may also be an external component open circuit. Observation TSC7106 foot {21} waveform should be 50Hz square wave, otherwise, it may be the internal 200 frequency divider damage.
Fourth, measure the component parameters.
For components within the scope of the fault, online measurement or offline measurement, parameter values should be analysed. For resistance online measurement, should consider the impact of the components connected in parallel with it.
Fifth, hidden fault elimination.
Hidden fault refers to the fault is hidden, the instrument is good or bad fault. Such failures are more complex, common causes include solder joints, loose, loose connectors, poor contact with the transfer switch, component performance is unstable, the lead will be broken and so on. In addition, also includes some external factors caused by. Such as high ambient temperature, excessive humidity or intermittent strong interference signals nearby and so on.
