Introduction to the Method of Measuring DC Working Voltage with a Multimeter
This is a method of measuring the DC supply voltage and the working voltage of peripheral components using the DC voltage range of a multimeter when the power is on. By detecting the DC voltage value of each pin of the IC relative to the ground and comparing it with the normal value, the scope of the fault can be narrowed down, and the damaged component can be identified. When measuring, the following eight points should be noted:
(1) The multimeter should have a sufficiently large internal resistance, at least more than 10 times the resistance of the measured circuit, to avoid causing large measurement errors.
(2) Usually, turn each potentiometer to the middle position. If it is a television, the signal source should use a standard color bar signal generator.
(3) Anti-slip measures should be taken for the test leads or probes. Since any momentary short circuit is likely to damage the IC. The following method can be adopted to prevent the test leads from slipping: Take a section of the valve core of a bicycle and put it on the tip of the test lead, making it about 0.5mm longer than the tip of the test lead. This can not only ensure good contact between the tip of the test lead and the test point, but also effectively prevent slipping. Even if it touches an adjacent point, there will be no short circuit.
(4) When the measured voltage of a certain pin is inconsistent with the normal value, it is necessary to analyze according to whether the voltage of this pin has an important impact on the normal operation of the IC and the corresponding changes in the voltages of other pins, so as to determine the quality of the IC.
(5) The pin voltage of the IC will be affected by the peripheral components. When the peripheral components have leakage, short circuit, open circuit or value change, or the peripheral circuit is connected to a potentiometer with variable resistance, the position of the sliding arm of the potentiometer will make the pin voltage change.
(6) If the voltages of all pins of the IC are normal, generally, the IC is considered to be normal; if the voltages of some pins of the IC are abnormal, it is necessary to start from the place where the deviation from the normal value is the largest, check whether there are faults in the peripheral components. If there is no fault, the IC is likely to be damaged.
(7) For dynamic receiving devices, such as televisions, the voltages of each pin of the IC are different when there is or is not a signal. If it is found that the voltage of a pin that should not change changes greatly, or the voltage that should change according to the size of the signal and the different positions of the adjustable components does not change, it can be determined that the IC is damaged.
(8) For devices with multiple working modes, such as video recorders, the voltages of each pin of the IC are also different under different working modes.
