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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 device cutoff area, amplification area and saturation area, but 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 we 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 distribution of circuit components and different signal solutions. With the current online testing technology, it is impossible to solve the online testing of analog chips. Therefore, the results of this functional test are for reference only.
. Most of the online testing programs will give a test passing r or a test failing r 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 factors that are affected (interference) during online testing. It is required to take many measures before testing (such as disconnecting the crystal oscillator, removing C and the chip with the program, adding isolation interrupt signals, etc.). Whether this is effective is worth studying. At least, 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. rThe explanation is that if the device is affected by online effects or resists interference, the result may not pass, which 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 that the chip is obviously damaged (to be precise, the board will not work if this chip is replaced), but the test result is 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.
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