Precautions for the maintenance of the hottest cir

Precautions for circuit board maintenance

precautions for circuit board maintenance

in the case of no directional vertical 25kg force front flat pressing any circuit schematic diagram on all sides of the tablet computer, it is difficult to deal with the past so-called maintenance experience to repair a strange and complex faulty circuit board Although the maintenance personnel with deep hardware skills of electronic technology are full of confidence in the maintenance work But if the method is improper, the work will still get half the result with twice the effort So, how can we better improve the maintenance efficiency

these are the principles to be discussed below for peer reference Make the maintenance work orderly and step by step

first, look and then measure the circuit board to be repaired. First, visually inspect it If necessary, observe with the help of a magnifying glass

mainly see:

1 Whether there is disconnection and short circuit; In particular, whether the connecting wire of the printed board on the circuit board is broken or adhered

2. Whether relevant components such as resistance, capacitance, inductance, diode, triode, etc. are disconnected

3. Has anyone repaired it? Which components have been moved? Whether there are problems such as faulty welding, missing welding, reverse insertion and wrong insertion

after the above conditions are eliminated, first measure the resistance between the power supply and ground of the circuit board with a multimeter. Generally, the resistance of the circuit board should not be less than 70 If the resistance is too small, it is only a few or more ohms It means that if there are components and parts on the circuit board that are broken down or partially broken down, measures must be taken to find the broken down components and parts The specific method is to power up the repaired board (note! At this time, be sure to make clear the voltage value and positive and negative polarity of the working voltage of the board, and do not connect wrongly or add higher than the working voltage value. Otherwise, the circuit board to be repaired will be damaged! The old faults have not been eliminated, and new faults will be added! Use a dot thermometer to measure the temperature of each device on the circuit board, and those whose temperature rises faster and higher are regarded as key suspects.

if the resistance value is normal, use a multimeter to measure the resistance capacitance devices on the board, such as diodes, triodes, field effect tubes, and Section switch and other components Its purpose is to first ensure that the measured components are normal Don't complicate problems that can be solved with general testing tools (such as multimeter, etc.)

II. Outside first and then inside

when using the circuit maintenance tester for detection If circumstances permit, it is best to have a good circuit board as the same as the board to be repaired as a reference Then use the double bar VI curve scanning function of the tester to compare the good and bad of the two boards The starting comparative test point can start from the port of the board where the plastic extruder industry in China is moving towards a healthy and sustainable development; Then from the outside to the inside, especially the comparative test of capacitors This can make up for the defect that the multimeter is difficult to detect whether the capacitor is leaking electricity

III. easy first, difficult later

when using the circuit maintenance tester for detection In order to improve the test effect, before the functional test of the circuit board, some technical treatment should be done to the repaired board to minimize the impact of various interferences on the test process Specific measures are as follows:

1 Preparation before the test

short circuit the crystal oscillator (note that for the four pin crystal oscillator, it is necessary to make sure that the two pins are signal output pins, which can be short circuited. Remember that the other two pins are power pins in general, and do not short circuited!!), For large capacity electrolytic capacitors, it is also necessary to weld the next pin to make it open circuit Because the charge and discharge of large capacity capacitors will also bring interference

2. Use exclusion method to test devices

in the process of testing or comparing devices, for devices that pass the test (or are relatively normal), please directly confirm the test results and record them If the test fails (or it is out of tolerance), the test can be conducted again If it still fails, you can also confirm the test results first This test continues until the devices on the board are tested (or compared) Then deal with those devices that fail the test (or are out of tolerance)

for devices that fail to pass the function test, some test instruments also provide a less formal but more practical treatment method: because the power supply of the test instrument to the circuit board can also be applied to the corresponding power and ground pins of the device through the test clip, if the power pin of the device is cut, the device will be separated from the circuit board power supply system

at this time, carry out function test on the device; Since other devices on the circuit board will not be powered on, the interference effect is eliminated At this time, the actual test effect will be equivalent to the quasi offline test, and the accuracy rate will be greatly improved

3. Asa-vi curve scanning test is used to compare the devices not covered by the test library

because asa-vi intelligent curve scanning technology can be applied to the comparative test of any device As long as the test clamp can clamp the device, there is another reference circuit board Through comparative test, it also has strong fault detection and judgment ability for devices This function makes up for the restriction that the device function test should be subject to the shortage of the device test library, and expands the detection range of the test instrument for the circuit board fault

in reality, it is often impossible to find a good circuit board for reference Moreover, the circuit structure of the board to be repaired does not have any symmetry. In this case, the asa-vi curve scanning comparison test function will not play a good role Due to the incompleteness of the device test library, the function test cannot be completed. Every device on the circuit board can be tested once, and the circuit board still cannot be tested This is the limitation of circuit maintenance tester It's like there is no medicine that can cure all diseases

fourth, first static and then dynamic

as for the current circuit maintenance tester, it can only carry out function test and static characteristic analysis on the devices on the circuit board Therefore, whether the faulty circuit board is finally completely repaired must be installed back on the original equipment for inspection In order to reduce the inspection process, the competition unit obtains the correct result to judge whether the circuit board is repaired At this time, it is best to check whether the power supply of the equipment is correctly supplied to the cost circuit board based on its combined thermoplastic polymer matrix as required, and whether all interface plug-ins on the circuit board are connected properly Be sure to eliminate the influence of the incorrect surrounding environment and peripheral circuits of the circuit board, otherwise the work of repairing the circuit board will be led astray