Multimeter DC Voltage Measurement Precautions
1. If you do not know the measured voltage range . Place the function switch in the maximum range and gradually decrease.
2,If the display only shows "1.", it means the range is too small, the function switch should be placed in a higher range.
3,"" means do not measure voltages higher than 1000V, displaying higher voltage values is possible but there is a danger of damaging the internal wiring.
4,When measuring high voltage, take extra care to avoid electric shock.
5, When selecting the function and range, the meter pen should leave the test point.
This is a kind of measurement of DC supply voltage and working voltage of peripheral components with DC voltage block of multimeter under power-on condition; detecting the DC voltage value of each pin of IC to the ground and comparing it with the normal value, thus compressing the scope of failure and finding out the damaged components. Measurement should pay attention to the following eight points:
(1) The multimeter should have a large enough internal resistance, at least 10 times greater than the resistance of the circuit under test, so as not to cause large measurement errors.
(2) Usually turn each potentiometer to the middle position, and if it is a TV set, the signal source should be a standard colour bar signal generator.
(3) The meter pen or probe should take anti-slip measures. Because any instantaneous short circuit is easy to damage the IC. the following method can be taken to prevent the meter pen from slipping: take a section of the bicycle with a valve core set on the tip of the meter pen, and long out of the tip of the meter pen about 0.5mm or so, which can make the tip of the meter pen good contact with the test point, but also effective in preventing slippage, even if it touches a neighbouring point will not be short-circuited.
(4) When measured a pin voltage does not match the normal value, the pin voltage should be based on the normal operation of the IC has no significant impact on the other pin voltage and the corresponding change in the analysis, in order to determine the good and bad IC.
(5) IC pin voltage will be affected by peripheral components. When the peripheral components leakage, short circuit, open circuit or change in value, or the peripheral circuit is connected to a potentiometer with variable resistance, then the potentiometer sliding arm is in a different position, will make the pin voltage change.
(6) If the IC pin voltage is normal, it is generally believed that the IC is normal; if the IC part of the pin voltage is abnormal, it should start from the largest deviation from the normal value, to check the peripheral components have no fault, if there is no fault, then the IC is likely to be damaged.
(7) For dynamic receiving devices, such as television sets, in the presence or absence of signal, IC pin voltage is different. If you find that the pin voltage should not change instead of large changes, the size of the signal and adjustable components with different positions and changes instead of changes, you can determine the IC damage.
(8) For a variety of operating modes of the device, such as video recorders, in different operating modes, IC pin voltage is also different.
