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Hello everyone, in this lesson we will talk about the troubleshooting of USB interface faults

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Before troubleshooting the USB interface failure, we need to know who the USB failure is related to

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Open the architecture diagram, you can see that the USB interface is controlled by the PCH

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Therefore, besides the USB interface circuit, the fault may also be related to the PCH.

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Next, let's take a look at the troubleshooting of a single USB interface that cannot be used

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If a single USB interface cannot be used,

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it is generally caused by a problem with the USB interface circuit.

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In this case, we first check the working conditions of the USB interface

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The working conditions of USB2.0 are very simple,

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that is, there is power supply, there is grounding, and the data line is normal.

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Therefore, the maintenance process is based on the workflow of the USB interface.

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First we need to check the appearance

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It is easiest to check the appearance

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Moreover, visual inspection can save us a lot of time

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After checking the appearance, we have to measure the power supply of the USB interface

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The power supply of the USB interface is 5V

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Just measure the voltage directly

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If the USB interface does not supply power,

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we have to trace the drawings or trace the circuit to see why there is no 5V power supply

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Next, we need to measure the USB2.0 data line to see if its ground value is normal

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Because the USB interface needs to communicate, the data line must be normal

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The easiest way to judge whether the data line is normal is to measure the ground value

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The ground values of D+ and D- are generally not much different, basically equal

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If we can't judge whether the value of the data line to ground is normal,

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we can refer to the normal USB interface

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If the ground value of the data line is abnormal, the anti-static diode or PCH may be damaged.

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Because the USB2.0 data cable generally only connects these two things

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And this anti-static diode is generally very close to the interface.

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The three components circled in the figure are anti-static diodes

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They are anti-static diodes for USB3.0 and USB2.0 data lines

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If the value of the data line to the ground is normal, but it still does not work,

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it may be caused by damage to the PCH or damage to the anti-static diode

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We can replace the anti-static diode and PCH in turn

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Next, let's look at the troubleshooting of all USB ports not working

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All the USB interfaces cannot be used, which means that the failure may not be caused by the interface circuit,

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but the working conditions of the PCH are not satisfied,

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or the USB module of the PCH is damaged.

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We're going to focus on inspecting the PCH.

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When we overhaul, we have to follow the principle of first easy and then difficult, first soft and then hard

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First of all, we still flash the BIOS first, and check whether there is any abnormality in the appearance

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After these two checks, measure the ground value of all USB2.0 data lines to see if they are normal

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Because in actual maintenance, it is often encountered that the USB2.0 data line is short-circuited

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The short circuit of the USB2.0 data line is generally caused by the PCH being damaged.

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If the PCH is damaged, it needs to be replaced

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If there is no problem with the data cable, it means that the USB module of the PCH is not working,

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or the USB module is not working properly

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The abnormal operation of the USB module may be caused by the bias resistor of the USB

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That is the pin circled in the picture on the right

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This pin is usually connected to ground using a resistor.

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If there is a problem with the resistance of this pin, the USB bus data will be abnormal,

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which will cause the USB interface to be unusable.

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If the bias resistance of the USB bias pin is normal, then we can try another PCH

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Generally speaking, if the USB interface is faulty,

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it is either the problem of the USB interface circuit or the problem of the PCH.

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It is relatively simple to repair the fault of USB interface