What are the general troubleshooting methods of digital multimeter?
Answer: Digital multimeter is a kind of measuring instrument which uses the principle of analog-to-digital conversion to convert the measured data into digital quantities and display the measured results in digital form. Compared with pointer multimeter, digital multimeter has the advantages of high precision, high speed, large input impedance, digital display, accurate reading, strong anti-interference ability and high measurement automation, so it should be widely used. However, if it is used improperly, it will easily lead to failure.
Troubleshooting of digital multimeter should generally start with power supply. For example, after turning on the power supply, if the LCD is not displayed, 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 order of "from inside to outside, from easy to difficult". Troubleshooting of digital multimeter can be roughly carried out as follows:
(1) Visual inspection:
You can touch whether the temperature of battery, resistor, transistor and integrated block is too high by hand. If the newly installed battery is hot, it means that the circuit may be short-circuited. In addition, you should also observe whether the circuit is broken, soldered, mechanically damaged, etc.
(2) detect the working voltage at all levels:
To detect the working voltage at all levels and compare it with the normal value, the accuracy of the reference voltage should be guaranteed first, and it is best to use a digital multimeter of the same model or similar to measure and compare it.
(3) waveform analysis:
Observe the voltage waveform, amplitude, period (frequency) of each key point of the circuit with an electronic oscilloscope. For example, test whether the clock oscillator starts to vibrate and whether the oscillation frequency is 40 kHz. If the oscillator has no output, it means that the internal inverter of TSC7106 is damaged, or the external components are open. Observe that the waveform of the {21st} pin of TSC7106 should be a 50 Hz square wave, otherwise, it may be the damage of the internal 200 frequency divider.
(4) Measuring element parameters:
For the components within the fault range, online measurement or offline measurement shall be conducted, and the parameter values shall be analyzed. When measuring the resistance online, the influence of the components connected in parallel should be considered.
(5) Hidden troubleshooting:
Implicit fault refers to the fault when the fault is hidden, and the instrument is good or bad. This kind of fault is complicated, and the common reasons include virtual welding of solder joints, loosening of connectors, poor contact of transfer switch, unstable performance of components, and continuous breakage of leads. In addition, it also includes some external factors. For example, the ambient temperature is too high, the humidity is too high or there are intermittent strong interference signals nearby.
