Under the circumstance of the absence of circuit schematic diagram, if you intend to repair a stange and complex faulty PCB circuit board, so called ¡±maintenance experience of PCB repair¡± can¡¯t take its effect anymore, Even the veteran electronic technology hardware repair personnel get half the result with double the effort, so what can be done to better improve the repair efficiency? The following principles will make the repair task being finished in an orderly and smooth way:
1 Visual inspection before any movement:
Inspect the PCB circuit board ready for repair visually first, take the advantage of magnifying glass when necessary; at this point you have to emphasis on:
And whether show the existence of cold solder£¬no solder and wrong/reverse component?
After all the conditions described above being excluded, now can use the multimeter to test the resistance value among power layer and ground layer, normally speaking the value shouldn¡¯t less than 70¦¸, if the resistance value less than that, for instance, only a few or a dozen ohms, that can illastrate that component(s) being breakdown, and then measure should be taken to find out what component(s) being breakdown, the most direct measure is supplying electric power to the circuit board (Note!!! Before that you have to figure out the working voltage and postive/negative polarity of the circuit board, the voltage must not allow higher than specified working voltage, otherwise circuit board will be damaged by it), point-temperature tester being applied to test the temperature of each component, the one whose temperature rise significant would be viewed as highly suspect item.
Once we can confirm the resistance value is normal, multimeter should be used again to test the diode, transistor, FET and bandswitch, etc. The purpose of all these actions is to ensure all the components tested are all normally function. Don¡¯t let the problem go further and become complicate if it only need multimeter to address it.
2 Check exterior and then interior:
When you inspect the PCB circuit board by using on-site circuit repair tester, it is more preferable that you can have a same normal function PCB circuit board in hand for reference, through which you can make the comparison test among these 2 PCB circuit boards by VI curve scanning function, PCB circuit board connector can be viewed as the starting point and then go further, especially for capacitor testing, which can solve the problem that multimeter can¡¯t if capacitor is leakage or not.
3 From easy to difficulty:
Before use on-site circuit maintenance tester to test the PCB circuit board, in order to ensure the accuracy, technical treatment can be done in advance to avoid the interference occurred during the testing, measures see below:
Make the crystal become SHORT circuit ( please be noted you have to clarify which 2 pins are the signal output pins and then make them SHORT circuit, under this condition the 2 other power pins must not be shorted of 4 leads crystal ), for those electrolytic capacitor, you have to make it become SHORT circuit first, because charging and discharging large-capacitance electrolytic capacitor will have interference too.
When use the on-site circuit maintenance tester to inspect all the components on the PCB circuit board, if the components pass the test and/or test result show it is normal, you can confirm the test result directly and make the record, for those fail to pass the test and/or test result show it is abnormal, test them one more time and if they still fail to pass the test then you can confirm the test result first, follow these ways and keep on testing all the components untill finish all the component test.
For those fail to pass the test, some testers have provided some very practical approach: this kind of tester can provide power supply to PCB circuit board through its clips, so in the same way it can supply power to component¡¯s POWER and GROUND pins, if lift the POWER pin of component from PCB circuit board manually then this component will be out of the power supply system of PCB circuit board.
At this time use the on-site tester to inspect component, because the other components can¡¯t being supplied by power so it will eliminate the interference effect and the testing circumstance equals to ¡°quasi-off test¡±, the percent of accuracy can be improved significantly.
4 From static to dynamic
Because on-site circuit maintenance tester can only inspect the components assembled on PCB circuit board and have the static characteristic analysis, therefore the way to conclude that whether the faulty PCB circuit board has been completely repaired is install it back to the original equipment and then test-run the equipment. Under this circumstance all the power supply of this equipment should be checked and ensure it can correctly provide power to the PCB circuit board, moreover all the connectors on it have been installed in good condition, the negative impact of incorrect connection of PCB circuit board must be eliminated completely.
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