Ten Techniques for Fault Diagnosis of Multimeters and Instruments
1. Tapping and Pressing Method
Intermittent malfunctions are mostly caused by poor contact or cold solder joints.Lightly strike circuit boards and components with a rubber hammer to check for errors or shutdowns. When faults occur, power off and firmly press connectors and sockets, then restart the device for verification. Re-seat all connections if tapping triggers unstable operation.
2. Visual Inspection Method
Diagnose faults via sight, smell and touch. Damaged components may discolor, blister or burn out. Burnt parts emit peculiar odors, short-circuited chips heat up obviously, and cold or detached solder joints can be observed directly.
3. Elimination Method
Remove internal plug-in boards and components one by one to locate faults. The malfunction lies in the part that restores normal operation after removal.
4. Replacement Method
Replace suspect components with intact spare parts of the same specification to verify whether faults disappear.
5. Comparison Method
Compare parameters between faulty and normal identical instruments with multimeters, oscilloscopes and other tools. Comparative items include voltage, waveform, static impedance, output and current. Deviations in measured signals indicate faulty positions.
6. Temperature Adjustment Method
Failures occurring under high temperature usually result from substandard high-temperature performance of chips and components.Cool suspicious parts with anhydrous alcohol to eliminate faults. Appropriately heat suspected areas with an electric iron to induce recurring malfunctions for confirmation, avoiding excessive heat damage.
7. Parallel Connection Method
Attach a functional integrated circuit or parallel qualified resistors, capacitors, diodes and transistors onto defective counterparts. This method works for internal open circuits and bad contact failures.
8. Capacitor Bypass Method
Connect capacitors across IC power pins and ground, or transistor base and collector terminals. Judge faulty circuit sections according to changes of abnormal phenomena such as display disorder.
9. State Adjustment Method
Mark original positions and record voltage or resistance values before adjusting potentiometers and adjustable parts. Proper parameter adjustment may eliminate hidden faults.
10. Isolation Method
Narrow down fault scope step by step following detection flowcharts. Combine with signal comparison and component swapping to quickly pinpoint failures without identical reference equipment.
