Judge Capacitor Quality by Multimeter
This is a detection method that detects the DC resistance of each pin of the IC in the circuit, the AC/DC voltage to ground, and the total operating current. This method overcomes the limitations of the substitution test method that requires replaceable ICs and the hassle of disassembling ICs, and is a commonly used and practical method for detecting ICs.
1. In circuit DC resistance detection method
This is a method of using a multimeter ohm range to directly measure the forward and reverse DC resistance values of various pins and peripheral components of the IC on the circuit board, and compare them with normal data to detect and determine faults. When measuring, pay attention to the following three points:
(1) Disconnect before measurement to avoid damaging the meter and components during testing.
(2) The internal voltage of the multimeter resistor range should not exceed 6V, and the range can be set to either R × 100 or R × 1k.
(3) When measuring IC pin parameters, attention should be paid to the measurement conditions, such as the tested model, the sliding arm position of potentiometers related to the IC, and the quality of peripheral circuit components.
2. DC working voltage measurement method
This is a method of measuring the DC supply voltage and the operating voltage of peripheral components using a multimeter's DC voltage range when powered on; Detect the DC voltage values of each pin of the IC to ground, compare them with normal values, and then compress the fault range to identify damaged components. When measuring, pay attention to the following eight points:
(1) A multimeter should have a sufficiently large internal resistance, at least 10 times greater than the resistance of the circuit being tested, to avoid significant 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) The probe or probe should be equipped with anti slip measures. Any momentary short circuit can easily damage the IC. The following methods can be taken to prevent the probe from sliding: take a section of the bicycle valve core and place it on the tip of the probe, and extend the probe tip by about 0.5mm. This can not only ensure good contact between the probe tip and the tested point, but also effectively prevent slipping, even if it touches adjacent points, it will not short-circuit.
(4) When the voltage of a certain pin does not match the normal value, it is necessary to analyze whether the voltage of that pin has a significant impact on the normal operation of the IC and the corresponding changes in the voltage of other pins in order to determine the quality of the IC.
(5) The voltage of IC pins will be affected by the periphery. When there is leakage, short circuit, open circuit, or value change in peripheral components, or when a potentiometer with variable resistance is connected to the peripheral circuit, the position of the potentiometer sliding arm will cause changes in the pin voltage.
(6) If the voltage of each pin of the IC is normal, it is generally considered that the IC is normal; If the voltage of the pins in the IC is abnormal, it should be checked for any faults in the peripheral components starting from the point where the deviation from the normal value is maximum. If there are no faults, the IC is likely to be damaged.
(7) For dynamic receiving devices such as televisions, the voltage at each pin of the IC varies with and without a signal. If it is found that the voltage of the pins should not change but instead changes significantly, and the voltage that should change with the signal size 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 voltage of each pin of the IC is also different under different working modes.
