How to Take Charged Measurements in PCB Circuit Board Repair?
The charged measurement method addresses two main areas. One is to break down the problems found and target them to the components that have problems. The second is that the problem has not been resolved, the need to identify the cause of the failure through bandwidth measurement. PCB bandwidth measurement method is mainly carried out through the following steps:
A. To the circuit board energized, in this step it should be noted that some circuit board power is not a single, may need 5V, will need positive and negative 12V, 24V, etc., do not add the power supply should be added to the leakage. After the circuit board is energized, by touching the components on the circuit board to see if there is a hot hot components, mainly to check the 74 series of chips, if the components have a hot hand, it is possible that this component has been damaged. After replacing the components, check whether the circuit board failure has been resolved.
B. Use an oscilloscope to measure the gate circuits on the circuit board and observe whether they conform to the logical relationship. If the output does not meet the logic, need to be divided into two cases treated separately, one is the output should be a low level, the actual measurement of the high level, you can directly judge the chip is damaged; the other is the output should be a high level, the actual measurement of low, and can not be judged in this regard the chip has been damaged, but also need to disconnect the chip and the back of the circuit, and then measure again, to observe the logic of whether it makes sense to determine the chip's good or bad.
C. Use an oscilloscope to measure the crystal in the digital circuit to see if there is an output. If there is no output, you need to be connected to the crystal as far as possible are removed from the chip and then measured. If there is no output, it is initially determined that the crystal has been damaged; if there is an output, you need to take off the chip one by one back to install a piece of measurement to find out where the fault lies.
D. Digital circuits with bus structure, generally including digital, address, control bus three-way. Measure the three buses with an oscilloscope, compare the schematic diagram, observe whether the signal is normal, and find out the problem.
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