What are the most common methods of troubleshooting on a digital multimeter?
Answer: Digital multimeter is a kind of measuring instrument which uses the principle of analogue/digital conversion to convert the measured quantity into digital quantity and display the measurement result in digital form. Digital multimeter compared with the pointer multimeter, with high precision, speed, input impedance, digital display, accurate readings, anti-interference ability, measurement of automation and other advantages of a high degree 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, if there is no LCD 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 order of "first inside and then outside, first easy and then difficult". Digital multimeter troubleshooting can be carried out in the following ways.
(1) Appearance check.
You can touch the battery, resistor, transistor, integrated block temperature is too high. If the newly installed battery heat, that the circuit may be short-circuited. In addition, should also observe whether the circuit is broken, desoldering, mechanical damage.
(2) Detect the working voltage at all levels.
Detect the working voltage at all levels and compare it with the normal value, first of all, the accuracy of the reference voltage should be ensured, it is best to use a piece of the same model or similar digital multimeter for measurement and comparison.
(3) Waveform analysis.
With an electronic oscilloscope to observe the circuit voltage waveforms at key points, amplitude, period (frequency) and so on. For example, measure whether the clock oscillator vibration, oscillation frequency is 40 kHz. if the oscillator has no output, that is, the TSC7106 internal inverter damage, may also be an external component open circuit. Observe the waveform of TSC7106 pin {21} should be 50 Hz square wave, otherwise, it may be the damage of internal 200 frequency divider.
(4) Measurement of component parameters.
Fault range of components, online measurement or offline measurement, should analyse the parameter values. For on-line measurement of resistors, the influence of components connected in parallel with them should be considered.
(5) Hidden fault elimination.
Hidden faults refers to faults that appear when hidden, the instrument is good or bad faults. This type of failure is more complex, common causes include solder joints, loose, loose connectors, poor contact with the adapter switch, component performance is unstable, the lead will be broken and so on. In addition, also includes some external factors. Such as high ambient temperature, high humidity or intermittent strong interference signal nearby.
