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Industrial circuit board repair skills
Don’t rely too much on online testers
. Functional testing cannot replace parameter testing
. Functional testing can only test the cut-off area and amplification area of the device In the saturation zone, it is impossible to know the working frequency and speed at this time.
. For digital chips, we only know the output changes of high and low levels, but cannot detect the changing speed of its rising and falling edges.
. For analog chips, it deals with simulated changes. It is intricately affected by the different distribution of components in the circuit and the different signal solutions. It is impossible to solve the online testing of analog chips with the current online testing technology. Therefore, the results of this functional test are for reference only.
. Most online test programs will give a pass or fail test after functional testing of various chips on the circuit board. So why doesn't it tell whether there is a problem with the device under test? This is the shortcoming of this type of tester. Because there are too many influencing (interfering) factors during online testing. It is required to take many measures before testing (such as disconnecting the crystal oscillator, removing the chip with program and isolating the interrupt signal, etc.) Whether this is effective is worthy of study. At least the current test results are sometimes unsatisfactory.
. Readers who know about online testers all know this jargon. A chip that fails the online test is not necessarily damaged, and a chip that passes the test must not be damaged. It is explained that if the device is affected by online influence or anti-interference, the result may not pass. This is not difficult to understand. So will damaged chips fail when tested? The answer is indeed not definite. The author and colleagues have all encountered cases where the chip was obviously damaged (to be precise, the board stopped working after replacing it) but the test result was passed. The authoritative explanation is that this is caused by the working principle of the tester itself (rear drive technology). Therefore, we cannot rely too much on the function of online testers (despite the mysterious propaganda of various manufacturers), otherwise the work of repairing circuit boards will go astray.
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Xiamen Yingyi Automation Technology Co., Ltd.
Contact person: Fu Maoqiang
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