Maintenance Skills of Industrial Circuit Board
Maintenance skill of industrial circuit board: Don't rely too much on online tester
The maintenance of industrial circuit boards is a technical activity, which requires a strong comprehensive ability of electronic circuit boards and manual operation. Before circuit board maintenance, it is necessary to identify problems. At this time, we need to use some professional testing instruments to capture abnormal data, eliminate potential problems item by item, and verify until the core of the problem is found. We can't rely too much on the selection of test instruments, otherwise it is easy to enter into a misunderstanding. Here are six aspects that need your attention.
1. Function test cannot replace parameter test.
2. The function test can only test the cut-off area, amplification area and saturation area of the device, but cannot understand the working frequency and speed at this time.
3. For digital chips, only the output changes of high and low levels are known, but the change speed of its rising and falling edges cannot be detected.
4. For analog chips, it deals with analog changes. It is complicated due to the distribution of circuit components and different signal solutions. With the current online testing technology, it is impossible to solve the problem of analog chip online testing. Therefore, the results of this functional test are only for reference.
5. Most online testing protocols will give "Test Passed" or "Test Failed" after functional testing of various chips on the circuit board. Then why does it not give whether there is a problem with the device under test? This is the lack of such testers. Because there are too many factors that affect (interfere with) online testing. It is required to take many measures before the test (such as disconnecting the crystal oscillator, removing the CPU and the chip with program, adding isolation interrupt signal, etc.). It is worth studying whether these measures are effective. At least, the current test results are sometimes unsatisfactory.
6. Readers who know about the online tester know such a jargon. "The chip that fails the online test is not necessarily damaged; the chip that passes the test must not be damaged." It is easy to understand that if the device is affected by online or anti-interference, the result may not pass. So, will the damaged chip "fail" when tested? The answer is really not sure. Both the author and his peers have encountered that the chip has been damaged (to be exact, it will not work if the chip board is replaced), but the test result is passed. The authority explained that this was caused by the working principle of the tester itself (rear drive technology). Therefore, we can not rely too much on the role of online testers (despite the hype of various manufacturers), otherwise the maintenance of circuit boards will go astray.
Any equipment is not omnipotent or stable forever. On the way to find and repair circuit board problems, it is necessary to have a certain skepticism and identify problems from multiple angles and dimensions, so as to find a repair solution.