Preventive measures for multimeter pointer bending and meter head burnt
1) Before measuring, estimate the size of the object being measured and turn the range switch to the appropriate range gear.
If you are not sure about the size being measured, you can first set the range to the maximum gear, and then slowly move towards the appropriate range gear.
Note that when measuring large objects with a small range, it is highly likely that the pointer will bend.
2) When measuring resistance, the tested circuit must be disconnected from the power supply.
3) Do not rotate the range switch when testing high voltage or high current. To prevent arcing at the contacts and damage to the switch.
4) When measuring electrolytic capacitors, first short-circuit and discharge them before measuring.
5) When using a multimeter incorrectly, the header may be burned.
Preventive measures: Connect two silicon diodes in parallel at the positive and negative ends of the meter head for protection (one in forward parallel and one in reverse parallel).
The conduction voltage of a silicon diode is generally greater than 0.5V, and below 0.5V, the forward resistance of the silicon diode is large, which has a small impact on the original internal resistance of the meter head and can be basically ignored.
When there is a false measurement, the increase in voltage will cause the forward resistance of the silicon diode to decrease, and most of the current will be diverted by the diode, which serves to protect the meter head.
Troubleshooting methods for hidden faults in digital multimeters
1. Waveform analysis.
Observe the voltage waveform, amplitude, period (frequency), etc. of each key point in the circuit using an electronic oscilloscope. For example, to test whether the clock oscillator starts oscillating and whether the oscillation frequency is 40kHz. If the oscillator has no output, it indicates that the TSC7106 internal inverter is damaged, or it may be an open circuit in external components. The waveform observed at pin {21} of TSC7106 should be a 50Hz square wave, otherwise it may be due to damage to the internal 200 frequency divider.
2. Measure component parameters.
For components within the fault range, online or offline measurements should be conducted, and parameter values should be analyzed. When measuring resistance online, the influence of components connected in parallel should be considered.
3. Hidden troubleshooting.
Hidden faults refer to faults that appear and disappear intermittently, with the instrument panel fluctuating between good and bad. This type of fault is quite complex, and common causes include virtual soldering of solder joints, loosening, loose connectors, poor contact of transfer switches, unstable component performance, and continuous breakage of leads. In addition, it also includes factors caused by external factors. Such as high ambient temperature, high humidity, or intermittent strong interference signals nearby.
4. Appearance inspection.
You can touch the temperature rise of the battery, resistor, transistor, and integrated block with your hand to check if it is too high. If the newly installed battery heats up, it indicates that the circuit may be short circuited. In addition, it is necessary to observe whether the circuit is broken, desoldered, mechanically damaged, etc.
5. Detect the working voltage at all levels.
To detect the working voltage at each point and compare it with the normal value, the accuracy of the reference voltage should be ensured first. It is best to use a digital multimeter of the same or similar model for measurement and comparison.
