Multimeter usage tips: DC working voltage measurement method

This is a method of measuring the DC supply voltage and the operating voltage of peripheral components with the DC voltage block of a multimeter under power-on conditions; detecting the DC voltage value of each IC pin to ground and comparing it with the normal value, thereby narrowing the fault range and finding the damaged components. Pay attention to the following eight points when measuring:

(1) The multimeter must have a sufficiently large internal resistance, at least 10 times greater than the resistance of the circuit being measured, to avoid large measurement errors.

(2) Normally, turn each potentiometer to the middle position. If it is a TV, the signal source should use a standard color bar signal generator.

(3) Anti-slip measures should be taken for the test leads or probes. Any instantaneous short circuit can easily damage the IC. The following method can be used to prevent the test leads from slipping: Take a section of bicycle valve core and put it on the tip of the test lead, and extend it about 0.5mm beyond the tip of the test lead. This can not only make the tip of the test lead contact well with the tested point, but also effectively prevent slipping, and will not cause a short circuit even if it touches an adjacent point.

(4) When the measured voltage of a certain pin is inconsistent with the normal value, the quality of the IC should be judged based on whether the pin voltage has a significant impact on the normal operation of the IC and the corresponding changes in other pin voltages.

(5) IC pin voltage will be affected by peripheral components. When peripheral components leak, short-circuit, open-circuit or change value, or the peripheral circuit is connected to a variable resistance potentiometer, the position of the potentiometer sliding arm will change, which will cause the pin voltage to change.

(6) If the voltages of all IC pins are normal, the IC is generally considered to be normal. If the voltages of some IC pins are abnormal, you should start from the point where the voltage deviates the most from the normal value and check whether there are any faults in the peripheral components. If there are no faults, the IC is likely to be damaged.

(7) For dynamic receiving devices, such as televisions, the voltages of the IC pins are different when there is a signal or not. If the voltage of a pin that should not change changes greatly, and the voltage of a pin 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 operating modes, such as video recorders, the voltages at each IC pin are different in different operating modes.