Repair Methods and Skills for Fluke Digital Multimeters
Fluke digital instruments have high sensitivity and accuracy, and their applications are almost ubiquitous in all enterprises. However, due to the multifactorial nature of its malfunctions and the high randomness of encountering problems, repairing it is difficult. I have compiled some repair experience accumulated from years of practical work for your reference and hope to be helpful to everyone.
1, Principles of repair methods
Finding faults should start with the outside and then the inside, starting with the easy and then the difficult, breaking down the whole into small parts and focusing on breakthroughs. The methods can be roughly divided into the following categories:
1. Sensory method relies on sensory perception to directly determine the cause of faults. Through visual inspection, it can detect issues such as broken wires, desoldering, short circuits in grounding, broken fuse tubes, burnt components, mechanical damage, copper foil warping and breakage on printed circuits, etc; You can touch the temperature rise of the battery, resistor, transistor, and integrated block, and refer to the circuit diagram to find the cause of the abnormal temperature rise. In addition, you can also check by hand whether the components are loose, whether the integrated circuit pins are firmly inserted, and whether the conversion switch is stuck; You can hear and smell any unusual sounds or odors.
2. The voltage measurement method measures whether the working voltage of each key point is normal, which can quickly identify the fault point. Measure the operating voltage, reference voltage, etc. of the A/D converter.
3. Short circuit method is generally used in the inspection of A/D converters mentioned earlier, and this method is more commonly used in repairing weak and micro electrical instruments.
4. The circuit breaking method interrupts the suspicious part from the entire machine or unit circuit. If the fault disappears, it indicates that the fault is in the disconnected circuit. This method is mainly suitable for situations where there is a short circuit in the circuit.
5. When the fault has narrowed down to a certain or several components, it can be measured online or offline using the component measurement method. If necessary, replace with good components. If the fault disappears, it indicates that the component is broken.
6. Interference method uses human induced voltage as an interference signal to observe the changes in LCD display, commonly used to check whether the input circuit and display part are intact.
2, Repair skills
For a faulty instrument, the first step is to check and distinguish whether the fault phenomenon is common (all functions cannot be measured) or individual (individual functions or individual ranges), and then differentiate the situation and solve it accordingly.
If all gears cannot work, the power supply circuit and A/D converter circuit should be checked carefully. When checking the power supply, remove the stacked battery, press the power switch, connect the positive probe to the negative power supply of the tested meter, and connect the negative probe to the positive power supply (for a digital multimeter). Turn the switch to the diode measurement mode. If the display shows the positive voltage of the diode, it indicates that the power supply is good. If the deviation is large, it indicates that there is a problem with the power supply. If there is an open circuit, focus on checking the power switch and battery leads. If a short circuit occurs, it is necessary to use the circuit breaking method to gradually disconnect the components that use the power supply, with a focus on checking the operational amplifier, timer, and A/D converter.
