Preventive measures for burnt head
1) Before measuring, estimate the size of the object to be measured, and turn the range switch to the appropriate range.
If you don't know the size to be measured, you can turn the range to the maximum first, and then slowly approach the appropriate range.
Note that when measuring a large object with a small range, 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) When testing high voltage or high current, it is forbidden to rotate the range switch. In order to prevent the contacts from arcing and damage the switch.
4) When measuring the electrolytic capacitor, it should be short-circuited and discharged before measuring.
5) When the multimeter is used incorrectly, the meter head may be burned.
Precautionary measures: connect two silicon diodes in parallel at the positive and negative ends of the meter head for protection (one forward parallel and one reverse parallel).
The conduction voltage of the silicon diode is generally greater than 0.5V, and the forward resistance of the silicon diode is very large below 0.5V, which has little effect on the original internal resistance of the meter and can basically be ignored.
Troubleshooting method of hidden fault of digital multimeter
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, if the clock oscillator starts to vibrate, whether the oscillation frequency is 40kHz. If the oscillator has no output, it means that the internal inverter of TSC7106 is damaged, or the external components may be open. Observe that the waveform at pin {21} of TSC7106 should be a 50Hz square wave, otherwise, the internal 200 frequency divider may be damaged.
2. Measuring component parameters.
For components within the fault range, conduct online or offline measurements, and analyze parameter values. When measuring resistance online, the influence of components connected in parallel with it should be considered.
3. Hidden troubleshooting.
Hidden faults refer to faults that appear and disappear from time to time, and the instrument is good and bad. This kind of failure is more complicated, and the common reasons include weak welding of solder joints, looseness, loose connectors, poor contact of transfer switches, 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.
4. Visual inspection.
You can touch the battery, resistors, transistors, and integrated blocks to see if the temperature rise is too high. If the newly installed battery heats up, the circuit may be short-circuited. In addition, the circuit should also be observed for disconnection, desoldering, mechanical damage, etc.
5. Detect the working voltage at all levels.
Detect the working voltage of each point and compare it with the normal value. First, ensure the accuracy of the reference voltage. It is best to use a digital multimeter of the same model or similar to measure and compare.
