Preventive measures for multimeter pointer bending and head burnout
1) Before measurement, estimate the size of the measurement and set the range switch to the appropriate range.
If you are not sure of the size of the measurement, you can first set the range to the maximum gear, and then slowly approach the appropriate range gear.
Note that when measuring a large measured object with a small range gear, it is very likely to bend the pointer.
(2) When measuring resistance, the circuit under test must be cut off from the power supply.
3) It is forbidden to rotate the range switch when testing high voltage or high current. In order to avoid contact arc, damage to the switch.
4) When measuring electrolytic capacitors, short-circuit and discharge them before measuring.
5) When using the multimeter incorrectly, the meter head may be burnt.
Preventive measures: Connect two silicon diodes in parallel with the positive and negative ends of the meter head to protect it (one forward parallel, one reverse parallel).
Silicon diode on voltage is generally greater than 0.5V, below 0.5V silicon diode forward resistance is very large, the original internal resistance of the meter head has a small impact, basically negligible.
When mismeasurement, the voltage rise will make the silicon diode forward resistance decrease, most of the current is shunted by the diode, play the role of protecting the meter head.
Digital multimeter hidden fault troubleshooting methods
1, waveform analysis.
Use an electronic oscilloscope to observe the voltage waveform, amplitude, period (frequency), etc. of each key point of the circuit. 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. Observe TSC7106 foot {21} waveform should be 50Hz square wave, otherwise, it may be the internal 200 frequency divider damage.
2, measuring 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.
3, hidden troubleshooting.
Hidden fault refers to the fault is hidden, the instrument is sometimes good and sometimes 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.
4, appearance check.
You can touch the battery, resistor, transistor, integrated block temperature rise is too high. If the newly loaded battery is hot, indicating that the circuit may be short-circuited. In addition, should also observe whether the circuit is broken, desoldering, mechanical damage.
5, test the working voltage at all levels.
Detect the operating voltage at various points, and compare with the normal value, first of all, should ensure the accuracy of the reference voltage, it is best to use a piece of the same model or similar digital multimeter for measurement and comparison.
