Some Troubleshooting Introductions for Digital Multimeters
A digital multimeter is a measuring instrument that uses the principle of analog/digital conversion to convert the measured value into a digital quantity and display the measurement result in digital form. Compared with the pointer multimeter, the digital multimeter has the advantages of high precision, fast speed, large input impedance, digital display, accurate reading, strong anti-interference ability, and high degree of measurement automation, so it is widely used. However, if used improperly, it is easy to cause failure.
Digital multimeter troubleshooting should generally start with the power supply. For example, after turning on the power, if the liquid crystal cell displays, you should first check whether the voltage of the 9V laminated battery is too low; whether the battery lead is disconnected. Finding faults should follow the order of "first inside and then outside, first easy and then difficult". Digital multimeter Troubleshooting can be roughly carried out as follows.
1. Appearance 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.
Second, 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.
3. 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.
4. 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.
5. 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, looseness of connectors, contact of transfer switches, unstable performance of components, and constant 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.
