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Nine key points to keep in mind when maintaining instruments and meters: 1. When using the ohm meter function of a multimeter, be sure not to take measurements on live circuits. 2. When using a logic probe or oscilloscope to detect signals, be careful not to let the probes make contact with two measurement pins at the same time, as this essentially creates a short circuit when power is applied. 3. When testing the filter capacitors in the power supply, the positive and negative terminals of the electrolytic capacitor should first be shorted together. Do not use the test leads as a substitute for wires to discharge the capacitor during this process, as this can easily cause the wire to burn out. A 220V, 60–100W lamp with a bulb lead can be used, connected across the capacitor; the bulb will flash at the moment of discharge. 4. When troubleshooting instrument faults in humid environments, it is essential to use a multimeter to check whether the various points on the printed circuit are conductive, as the main issue in such cases is copper foil corrosion. 5. When repairing the internal circuits of instruments, if the contacts of the components and the circuit board are coated with insulating varnish, a regular sewing needle can be soldered to the probes of a multimeter in order to pierce through the varnish layer and measure the parameters at various points, thereby avoiding the need to remove a large area of the varnish layer. 6. Do not plug or unplug various control boards and plugs while they are powered on. Because when the power is on, plugging in or removing the control board generates a strong induced electromotive force; at this time the reverse voltage is very high, which can easily damage the corresponding control board and plug. 7. During maintenance, do not strike or touch things randomly to avoid exacerbating the fault and making it worse. 8. When removing or adjusting instruments, their original positions should be recorded for restoration. 9. When repairing precision instruments, if small parts are accidentally sent flying, one should first determine where they might have fallen; there’s no need to search around randomly. Magnets and visual inspection can be used to locate them. In short, in the maintenance of instruments and meters, it is first necessary to understand the basic principles of these instruments, as well as to master relevant electronic knowledge and skills. It is also important to have available all technical documents such as manuals and diagrams for the instruments and meters. Additionally, developing good work habits is essential in order to improve efficiency and reduce errors during the maintenance process.