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The following are some principles to be discussed for reference by PCB peers. Make maintenance work orderly.
Principle 1: Look at the quantity first.
The repaired circuit board should be visually inspected first. If necessary, observe with a magnifying glass.
Mainly look:
1: Whether there is disconnection or short circuit, especially whether the printed circuit board is broken or not;
(2) Whether there is any disconnection in the relevant PCB components, such as resistors, capacitors, inductance diodes;
3: Has anyone repaired it? Which components did you move? Whether there are problems such as false weld leakage and post-insertion errors.
After excluding the above conditions, an electric meter should be used to measure the resistance between the power supply and the circuit board ground. If the resistance is too small, there are only a few ohms or more than ten ohms. Indicates that a component on the board has been punctured or partially punctured, and measures must be taken to find the component to be punctured. The specific method is to power up the board to be repaired (note!). This is very important. It is important to understand that the voltage value of the board's working voltage cannot be connected wrongly, and the input voltage must be higher than the working voltage.
Voltage value. Otherwise it will damage the repair circuit board! Old errors have not been eliminated, and new problems have been added! ! The temperature of each device on the circuit board is measured with a spot thermometer, and faster and higher temperature rises are considered key suspicious objects.
If the resistance value is normal, use a multimeter to measure the second part of the blocked container, the three-pole field effect tube and the peeling part switch and other components. The purpose is to first ensure that the component under test is normal. Don't complicate the problems that general test tools (for example, utility tables, etc.) can solve.
Principle 2: First, external, then internal.
If possible, it is best to use a circuit board as good as the circuit board to be repaired as a reference. Then, use the double-edge VI curve scanning function of the tester to test the contrast of the two boards. The comparison test point can start from the port of the circuit board, and then test through the comparison of the table and the capacitor. This makes up for the shortcomings of the meter online, which makes it difficult to detect whether the capacitor is leaking.
Principle 3: Difficulties first, then difficult.
In order to improve the test effect, before the online function test, the single board should be repaired and some technical processing should be carried out to minimize the influence of various interferences on the test process. The specific measures are as follows:
1: Pre-test preparation.
Short-circuit the crystal oscillator (please note that the four-pin crystal oscillator can find out which pin is the signal output pin, and you can short-circuit these two pins.) Please remember that in general, the other two pins of the power pin must not be short! For large-capacity electrolytic capacitors, the next leg needs to be soldered to disconnect the circuit. Because the charging and discharging of large capacitors can also cause interference.
2: The device passed the exclusion test.
During online or comparative testing of equipment, the PCB factory can record all passing (or more normal) equipment by directly confirming the test results. If the test fails (or worse), test again. If it still fails, you can confirm the test result first. It will continue testing until the device test (or comparison) on the board is completed. Then dispose of devices that fail the test (or worse).
Some test instruments for equipment that cannot pass the online test also provide a less formal but more practical approach: because the test instrument can also be applied to the corresponding power and ground pins of the device through a test clip, remove the device From the onboard power system.
