10 Methods for Fault Diagnosis of Multimeters and Other Instruments
1. Percussion hand pressure method
It is often encountered that the instrument runs up and down when it is running, and most of this phenomenon is caused by contact or virtual welding. In this case, tapping and hand pressing can be used. The so-called "knocking" is to gently tap the plug-in board or components with a small rubber hammer or other knocking objects on the parts that may fail to see if it will cause errors or shutdowns. The so-called "hand pressure" means that when a fault occurs, turn off the power and re-press the inserted parts, plugs and seats by hand, and then try to turn on the power to see if the fault will be eliminated. If it is found that it is normal to knock on the case once, and it is not normal to knock again, it is best to reinsert all the connectors and try again. If the brain is not successful, you have to find another way.
2. Observation method
Use sight, smell, touch. Sometimes, damaged components will discolor, blister or burnt spots; burnt out components will produce some special smells; short-circuited chips will become hot; weak soldering or desoldering can also be observed with the naked eye .
3. Exclusion method
The so-called elimination method is to judge the cause of the failure by unplugging and inserting some plug-in boards and devices in the machine. When the instrument returns to normal after a certain plug-in board or device is unplugged, it means that the fault occurred there.
4. Replacement method
Two instruments of the same model or sufficient spare parts are required. Replace a good spare with the same component on the faulty machine to see if the fault is eliminated.
5. Contrast method
It is required to have two meters of the same model, and one of them is in normal operation. Using this method also has the necessary equipment, for example, multimeter, oscilloscope, etc. According to the nature of the comparison, there are voltage comparison, waveform comparison, static impedance comparison, output result comparison, current comparison, etc. The specific method is: let the faulty meter and the normal meter run under the same conditions, and then detect the signals of some points and compare the two groups of signals measured. If there is a difference, it can be concluded that the fault is here. This method requires maintenance personnel to have considerable knowledge and skills. Ten Methods for Fault Diagnosis of Multimeters and Other Instruments
6. Heating and heating method
Sometimes, the meter works for a long time, or when the temperature of the working environment is high in summer, it will fail. It is normal to shut down and check. This phenomenon is due to the poor performance of individual ICs or components, and the high temperature characteristic parameters cannot meet the index requirements. In order to find out the cause of the failure, the heating and cooling method can be used. The so-called cooling means that when a fault occurs, use cotton fiber to wipe anhydrous alcohol on the part that may be faulty to cool it down and observe whether the fault is eliminated. The so-called temperature rise is to artificially increase the ambient temperature, such as putting an electric soldering iron close to suspicious parts (be careful not to raise the temperature too high to damage normal devices) to see if the fault occurs.
7. Shoulder riding
The shoulder riding method is also called the parallel method. Install a good IC chip on the chip to be checked, or connect good components (resistors, capacitors, diodes, triodes, etc.) Exposure to drugs and other reasons can be ruled out by using this method.
8. Capacitor bypass method
When a certain circuit produces a strange phenomenon, such as the display being confused, the capacitor bypass method can be used to determine the probably faulty circuit part. Connect the capacitor across the power supply and ground of the IC; connect the transistor circuit across the base input or collector output, and observe the impact on the fault phenomenon. If the bypass input of the capacitor is ineffective and the symptom disappears when bypassing its output, the fault is determined to be in the circuit.
9. State adjustment method
Generally speaking, before the fault is determined, do not touch the components in the circuit casually, especially for adjustable devices, such as potentiometers. However, if re-referencing measures are taken in advance (for example, the position is marked or the voltage or resistance value is measured before the touch), it is still allowed to touch if necessary. Maybe after a change sometimes the glitch goes away.
10. Isolation method
The fault isolation method does not require comparison of equipment or spare parts of the same type and is reliable. According to the fault detection flow chart, segmentation and encirclement gradually narrow the fault search range, and then cooperate with signal comparison, component exchange and other methods, generally the fault will be found quickly.
