The method of measuring the 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 to the ground and comparing it with the normal value, the fault range can be narrowed down and the damaged component can be found. When measuring, the following eight points should be noted:
(1) The multimeter should have a large enough internal resistance, at least more than 10 times the resistance of the circuit under test, to avoid causing large measurement errors.
(2) Generally, turn each potentiometer to the middle position. If it is a television, a standard color bar signal generator should be used as the signal source.
(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 protrude about 0.5mm from the tip of the test lead. This can not only ensure a good contact between the tip of the test lead and the test point, but also effectively prevent slipping. Even if it touches the adjacent point, it will not cause a short circuit.
(4) When the voltage of a certain pin is inconsistent with the normal value, the quality of the IC should be judged by analyzing the influence of the pin voltage on the normal operation of the IC and the corresponding changes in the voltages of other pins.
(5) The voltage of the pins 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 a variable resistance, the voltage of the pins will change depending on the position of the sliding arm of the potentiometer.
(6) If the voltages of all pins of the IC are normal, the IC is generally considered to be normal. If the voltages of some pins of the IC are abnormal, the inspection should start from the pin with the largest deviation from the normal value to check whether the peripheral components have faults. 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 pin voltage that should not change changes greatly, and the pin voltage that should change according to the size of the signal and the position of the adjustable component 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.
