Some methods of instrumentation fault diagnosis

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1. Tapping Pressure Method

This method is commonly used when an instrument is functioning properly but occasionally experiences issues, usually due to poor contact or solder joint problems. In such cases, gently tapping the board with a small rubber hammer or using hand pressure can help identify and resolve the problem.

The term "tapping" refers to lightly knocking on the board or component with a small rubber hammer or similar object to see if it causes any errors or system shutdowns. The "hand pressure" technique involves pressing the inserted components and connectors firmly after turning off the power when a fault occurs, then re-powering the device to see if the issue is resolved. If the casing appears normal but the tapping doesn't work, reinserting all connections and testing again is recommended. If this fails, other troubleshooting methods must be considered.

2. Observation Method

This method relies on visual inspection, smell, and touch. Damaged components may show discoloration, blistering, or burn marks. Burned devices often emit a distinct odor, while short-circuited chips may feel hot. Visible or desoldered parts can also be identified by the naked eye, making this a simple yet effective diagnostic tool.

3. Elimination Method

The elimination method involves plugging in or removing internal boards and devices to determine the source of the fault. If the instrument returns to normal after removing a specific board or component, the fault is likely located there. This method helps isolate the problem efficiently.

4. Replacement Method

This approach requires having two identical instruments or sufficient spare parts. By replacing a faulty component with a known good one, you can determine whether the issue has been resolved. It's a practical solution when the exact cause is unclear.

5. Comparison Method

This method involves comparing two identical instruments, one of which is functioning normally. Using tools like multimeters, oscilloscopes, or other equipment, you can compare voltages, waveforms, static impedance, output signals, and current values. This helps identify discrepancies that indicate a fault.

For example, run both the faulty and normal instruments under the same conditions, measure signals at key points, and compare the results. If differences are found, the fault is likely in that area. This method demands a high level of technical knowledge and experience from the technician.

6. Temperature Rise and Fall Method

Sometimes, instruments may fail after prolonged use or during high-temperature environments, only to return to normal after cooling down. This is often caused by components with poor thermal performance, such as ICs that fail under heat. To diagnose this, the temperature rise and fall method is used.

The cooling technique involves applying anhydrous alcohol to suspected areas with a cotton swab to lower the temperature and observe if the fault disappears. The heating technique involves using a soldering iron (with caution to avoid overheating) to raise the temperature of a suspected component and check for recurring faults.

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