Multimeter to find line faults of the voltage check method
Voltage checking method uses a multimeter to find out the voltage abnormality, and make inferences based on the voltage changes and the working principle of the circuit to find out the specific cause of the fault.
Principle of voltage checking method
Through the detection of certain test points in the circuit voltage or not, large or small, to determine the cause of voltage changes, the reason is the cause of the failure.
Circuit in normal operation, each part of the working voltage value is unique, when the circuit has an open circuit, short circuit, component performance changes, etc., the voltage value is bound to have a corresponding change, the voltage check method is to detect this change, and then analyze.
Voltage inspection method of measurement objects
Electronic circuits have the following main types of voltage.
1, AC mains voltage, 220V, 50Hz.
2, AC low voltage, ranging from a few volts to tens of volts.
3, DC operating voltage, may be a few volts to tens of volts, may be hundreds of volts or even higher (video equipment may be as high as tens of thousands of volts).
4, audio signal voltage, a few millivolts to tens of volts.
Measurement of AC voltage
1, measuring AC mains voltage
Multimeter adjusted to AC 750V gear (different multimeter gear may be different), measure the power transformer primary winding ends, there should be 220V, if not, check whether the power jack is not connected or no power.
2、Measure AC low voltage
Select the appropriate range of the multimeter AC voltage gear, measure the output voltage of the secondary side of the power transformer, in the case of confirming that the input voltage is normal, if there is no low-voltage output, most of the power transformer primary winding is open-circuit, there is a small probability that the secondary winding may be disconnected.
Measurement of DC voltage
Measurement of DC voltage, select the appropriate DC voltage gear, black pen grounding, red pen reception measurement point, according to the measurement results.
1, the machine DC voltage when no-load than when working several volts higher, the higher the power supply resistance is greater.
2, the machine in the rectifier circuit output DC voltage is the highest, along the RC filter, decoupling circuit gradually decreased.
3, polarized electrolytic capacitor voltage, the positive end is higher than the negative end.
4, if the capacitor ends of the voltage is zero, as long as the circuit has a DC work, it means that the capacitor has been short-circuited. DC voltage at both ends of the inductor should be close to zero, otherwise it is an open-circuit fault.
5, the circuit has a DC operating voltage, the resistor should have a voltage drop at both ends, otherwise the resistor circuit is faulty.
6, DC voltage at both ends of the inductor is not zero, indicating that the inductor is open.
Voltage check method features
1, when measuring voltage, the multimeter is connected in parallel, no need for components, circuits to make any adjustments, easy to operate
2、The voltage data in the circuit is reliable for the judgment of the fault.
3、Detailed and accurate voltage measurement requires the relevant voltage data in the circuit diagram of the whole machine.
Sixth, the scope of application of the voltage inspection method
1, AC circuit failure
2, DC circuit failure
3, other circuit faults
