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In this lesson, let's talk about troubleshooting ideas for digital interfaces that do not display

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Let's take the HDMI interface as an example

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The fault phenomenon is that the computer has been turned on, but there is no display

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Here we must pay attention to distinguish between failures that do not display and failures that do not start

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We can judge whether the computer is turned on by the uppercase and lowercase lights of the keyboard

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or the sound of entering the system.

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Only when the computer is turned on and the display is not displayed is the fault not displayed

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The failure to display is generally caused by the unsatisfactory working conditions of the interface,

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or a problem with the data line of the interface.

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We still have to follow the maintenance principle of soft first,

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then hard, and first easy and then difficult.

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First check for cosmetic faults

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If there is an appearance fault,

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we should first solve the appearance fault before proceeding to the next step of maintenance

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After checking the appearance, we will follow the workflow of the interface to overhaul

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First check whether the power supply pin of the interface is powered

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HDMI power supply is 5V, DP interface is 3.3V

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After the power supply is available, it is necessary to detect

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whether the HPD interface has a high level after plugging in the line

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The HPD signal is generally high after the display line is inserted

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At the same time, we also need to check whether the HPD signal is sent to the CPU,

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whether there is a disconnection in the middle, or whether there is a conversion error in the conversion circuit

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After checking the power supply and plug-in detection, we will check the data cable next.

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Measure whether the ground value of the serial bus is normal

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If the ground value is normal, we will measure the data line

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and clock line of the display signal line to see if their ground value is normal

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It should be noted here that there will be a coupling capacitor between the display signal and the clock signal

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We have to measure at the end of the coupling capacitor close to the CPU to get the correct value

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If the ground values are all normal, we will use an oscilloscope to measure,

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and measure whether the screen reading signal has a waveform

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If there is a waveform, it means that the CPU has gone to read the screen

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If there is no waveform, it means that the CPU has not read the screen

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We have to check whether there is a problem with the screen reading line,

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or whether the CPU has sent a screen reading signal

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Under normal circumstances, as long as the CPU receives the HPD signal, it will send a screen reading signal

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However, the transmission rate of these display signal lines is relatively high,

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and it is not easy to measure with an oscilloscope.

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And even if it has a problem, there is no way to fix it

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So we generally just replace the coupling capacitor directly.

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If there is no problem after all these tests, but the screen still does not display,

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then you can only replace the CPU or the CPU seat

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In general, the maintenance process that is not displayed on the digital interface is actually

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in accordance with the maintenance process of the interface

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Check whether there is power supply, whether there is HPD,

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whether there is a screen reader, and whether there is a display signal

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Well, the above are the maintenance procedures that the digital interface does not display