Detection of external AC voltage and DC voltage of internal circuit is the basis of fault analysis. Therefore, in the process of overhauling electrical and electronic circuit adjustment, the relevant voltage should be measured first, so that problems will often be found and faults found.

　　The voltage measurement method is to measure the voltage of each part of the electrical or electronic circuit under test and compare it with the normal value to find out the fault location.


　　In the process of maintenance, even if the fault location of the circuit has been determined, it is necessary to further measure the voltage of the transistors, integrated circuits and other pins in the, integrated circuit, or the voltage value of the main node in the circuit to see if it is normal. This is helpful to find damaged components and analyze the cause of failure.

　　For the circuit which is not convenient to measure the current, the voltage at both ends of the resistor flowing through the current is often measured, and then indirectly calculated by means of Ohm's law (this method is also called indirect current testing method). For example, semiconductor transistor current negative feedback amplifier circuit and emitter output transistor static working point ICQ, this method is commonly used to measure. However, the error of this method is due to the error between the actual resistance value and the nominal value, and the change of the resistance value after the long-term use of the resistor, especially the carbon film resistance.

　　Measuring the input or output signal voltage of the electronic circuit to check whether the dynamic working state is normal also belongs to the category of voltage measurement method.

　　(1) Methodological essentials:

　　Select the appropriate range of AC voltmeter or DC voltmeter (universal multimeter),<0 corresponding power supply voltage.

　　Select the appropriate range and high input impedance of the electronic voltmeter to measure the relevant node or device electrode operating voltage.

　　Select the appropriate range and frequency range of electronic voltmeter to measure the relevant circuit input and output signal voltage.

　　Find out the fault area against normal value. Where the voltage deviates from the normal value, it is often the fault location.

　　(2) Notes:

　　1 Attention should be paid to the "I" polarity of the DC voltmeter to determine the direction of the voltage or current.

　　Attention should be paid to the relative measurement of the working voltage: generally to the ground wire (that is, to the housing), some to zero volts selected, some between the electrodes, need to be classified, careful testing.

　　Attention should be paid to the order of "high" potential and "low" potential. The "ground" potential end (i.e. ground line) should be first connected to the "high" potential end. After measurement, the "high" potential end should be removed first, and then the "low" potential end should be removed.

　　Attention should be paid to the influence of the input impedance and frequency range of the voltmeter on the test results.

　　Measuring the input or output signal voltage of the electronic circuit to check whether the dynamic working state is normal also belongs to the category of voltage measurement method.


　　(1) Methodological essentials:

　　Select the appropriate range of AC voltmeter or DC voltmeter (universal multimeter),<0 corresponding power supply voltage.

　　Select the appropriate range and high input impedance of the electronic voltmeter to measure the relevant node or device electrode operating voltage.

　　Select the appropriate range and frequency range of electronic voltmeter to measure the relevant circuit input and output signal voltage.

　　Find out the fault area against normal value. Where the voltage deviates from the normal value, it is often the fault location.

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