PCB Technical - Industrial circuit board repair skills: can't rely too much on online testers

Industrial circuit board repair skills: can't rely too much on online testers

Industrial circuit board repair is a technical activity that requires a strong comprehensive ability in electronic circuits and manual operations. Before the circuit board is repaired, it is necessary to identify the problem first. At this time, we need to use some professional testing equipment to capture abnormal data, eliminate potential problems one by one, and pass verification until the core of the problem is found. We cannot rely too much on the selection of test instruments, otherwise it is easy to get into misunderstandings. Here are 6 aspects that you need to care about.

1. Function test cannot replace parameter test.

2. The function test can only test the cut-off area, the amplification area and the saturation area of the device, but it is impossible to know the level of the operating frequency and the speed at this time.

3. For digital chips, only the output changes of high and low levels are known, but the changing speed of its rising and falling edges cannot be detected.

4. For an analog chip, it deals with the amount of change in the simulation. 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.

5. In most online test sessions, after performing functional tests on various types of chips on the circuit board, they will give "test passed" or "test failed". So why doesn't it tell if there is a problem with the device under test? This is the shortcoming of this type of tester. Because there are too many factors affected (interference) during online testing. It is required to take a lot of measures before the test (such as disconnecting the crystal oscillator, removing the CPU and the chip with the program, adding an isolated interrupt signal, etc.). Whether this is all effective is worth studying. At least, the current test results are sometimes unsatisfactory.

6. Readers who know the online tester know that there is such a jargon. "The chip that failed in the online test is not necessarily damaged; the chip that passed the test must not be damaged." Its explanation is that if the device is affected by online or anti-interference, the result may not pass, which is not difficult to understand . So, whether the damaged chip will be "failed" during the test? The answer is indeed uncertain. Both the author and my colleagues have encountered it. It is clear that the chip has been damaged (to be precise if it is replaced with this chip board and it will not work), but the test result is passed. The authoritative explanation is that this is caused by the working principle of the tester itself (post-drive technology). Therefore, we cannot rely too much on the role of the online tester (although the various manufacturers advertise it), otherwise the work of repairing the circuit board will go astray.

Any equipment is not a panacea, nor is it always stable. On the road of discovering and repairing circuit board problems, it is necessary to have a certain spirit of suspicion, and comprehensively identify the problems from multiple angles and dimensions, so as to find a repair solution.

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