Recently, customers in the LED display rental industry have reported to the sales staff of the company: "There are a lot of activities during the Spring Festival, and there is a problem that the processor input port cannot recognize the signal. What is the reason?" After the machine returns, we have confirmed that the cause of the failure is that the processing chip or protection chip of the input port is damaged. In order to further eliminate the processor itself, we also specially sent the repaired processor to the test company for electrostatic testing. After confirming that the reliability of the processor itself is no problem. Why is the processor port chip and the protection chip damaged? I share my understanding of this and hope to discuss it with you.
I. Electrostatic discharge (ESD) and countermeasures
The most common cause of damage to electronic components is electrostatic discharge (ESD). Especially in the dry winter, we wear more sweaters and other clothes that are easy to generate static electricity. The human body may even generate tens of thousands of volts of static electricity, so that direct touch of the processor port can cause component damage.
The countermeasure to avoid this problem is to firstly touch the device that is effectively grounded to remove static electricity when contacting a device such as a processor, so that when the device is touched, it is relatively safe.
In order to deal with the damage of the motherboard components caused by the electrostatic discharge, the data pins of the input and output ports of the only video processor products are equipped with protection devices such as TVS tubes.
However, one of the prerequisites for the maximum protection of the device is effective grounding. Because the common protection device is connected to the data pin at one end and grounded at the other end, so that high voltages such as static electricity are connected to the data pins, and these protection devices are short-circuited and passed through the ground. The line is vented and the components in the rear section are protected from damage (TVS tube in position D66 below).
Protective element schematic
II. Leakage current damage
The leakage current of the device also causes the port chip to be burned. First we first understand the concept of leakage current.
In order to reduce interference in the switching power supply, there will be a corresponding EMI filter circuit. However, the existence of the EMI circuit causes a small current to the ground after the switching power supply is connected to the market, which is the leakage current.
For devices such as processors, if the case is not grounded or the power cord has no ground wire, the device will have 110 volts to the ground after the device is powered, so that people directly touch the metal casing of the device. At this time, if the processor and the signal source have one ground and the other is not grounded, a spark will be seen when the signal is plugged or unplugged. If the signal cable plug first contacts the data pin (unconventional case), it will burn out. The internal chip of the signal or signal, as shown below, is the processor rework machine, the chip corresponding to the motherboard port, the protection component and the PCB have been burned out.
Countermeasures:
1. The best method is to ground, the processor and signal source are grounded by ground wire, and the multimeter is used to test the impedance to ground or no AC voltage to the ground, so that even if the plug is powered, there is no problem.
2. If the grounding of the power socket of the site is not guaranteed, it is better to connect the signal cable first, and then connect the power cable to the power cable. Do not plug in the signal!
The following figure shows an example: first connect the signal line between the LVP605 and the computer monitor and the sending card, then connect each device to the power cable between the power strips, and finally power on.
The importance of grounding
As mentioned above, grounding is the premise that ESD protection devices really play the most important role, and it can also avoid the leakage current to the human body damage, and the importance of grounding can be seen.
Grounding is an electrical safety measure adopted to ensure the normal operation and personal safety of electrical equipment. It is realized by connecting metal wires to grounding devices. Commonly used are protective grounding, working grounding, lightning protection grounding, shielding grounding, and anti-static grounding. Wait. The grounding device introduces leakage current, static charge and lightning current generated on electrical equipment and other production equipment into the ground, thereby avoiding personal electric shock and possible fire, explosion and other accidents.
However, due to actual conditions, when using the processor and other equipment, it is impossible to achieve reliable grounding. When using it, you must pay attention to the precautions mentioned above. The important things are repeated:
1. Before touching the device, touch the ground wire or other effectively grounded metal case to remove static electricity.
2. Connect the signal cable first when wiring, and then connect the power cable to power.
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