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In this lesson, we will talk about the maintenance of the fault that

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the mobile phone starts normally but cannot be displayed

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We talk about it mainly from the following aspects

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First, the current phenomenon that mobile phone starts normally but cannot be displayed

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Second, the general cause of this failure

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Third, the working condition of the display circuit

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Fourth, what circuit is related to the display circuit,

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or what the display circuit contains

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The last is how to repair this fault

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Let's take a look at the current phenomenon that the mobile phone does not display

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but can boot into the system normally

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When we repair a mobile phone that does not display,

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first of all, the premise is that the mobile phone can be turned on normally,

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that is, it can enter the system normally

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We mainly look at its take-off current,

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and whether the current can increase gradually,

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and reach a maximum current,

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and then fall back to about 100 to 200 mA

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Such a jump process is a process that can normally boot into the system

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When we see a mobile phone with such a current change,

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but it cannot display, the display does not respond,

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we think it just boots normally but doesn't display

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Okay, let's take a look at its current

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After pressing the power button, the current does not change

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Now the current jumps for a while,

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four or five hundred, more than five hundred to one ampere

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Now it's one thousand eighteen, one thousand seventeen, about two amps

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But some machines do not have such a large maximum current

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It's back down now, back down to three or four hundred

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At this time, it has actually entered the system

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When we see this current phenomenon,

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the phone can basically be concluded that it can be turned on normally,

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it just does not display

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At this time, we are going to repair the display circuit,

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and check whether it is a screen problem that causes the display not to be displayed

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Ok, this is the judgment of the current that can be turned on but not displayed

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Let's take a look, in the actual maintenance,

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many people regard the non-boot as the non-display,

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which has such a misunderstanding

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How to make sure that a mobile phone can be booted into the system but not displayed?

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There are mainly the following methods

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First, observe the current.

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We judge by the current entering the system when it is turned on normally

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This is the method we used just now, it is called the current method

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Second, install a SIM card in the phone and use another phone to dial the number

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If the phone has an incoming call prompt sound,

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it means that the phone can be turned on to enter the system, but does not display

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There is another method, for example,

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the display of the mobile phone cannot be displayed,

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but there is an alarm sound

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Indicates that the phone can be turned on but does not display

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Okay, that's it for this lesson