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In this lesson, we're going to learn about the maintenance of Apple laptop boot without display fault

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There are usually 5 phenomena of boot without display fault

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First, let's look at the first failure phenomenon

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The first failure phenomenon is that after pressing the switch,

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it can trigger power-on, but the current does not jump

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For example, the current jumps to 0.093A, and then it can no longer go up

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At this time, we can measure each power supply on the mainboard to see if any power supply is not generated

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As low as this current, it is generally a lack of power supply

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We focus on checking the main power supplies controlled by SLP_S3# and SLP_S4#,

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as well as the secondary voltage

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We can also use the platform reset signal as an entry point to check whether there is a high-level reset signal

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According to the Intel standard timing, if there is a reset signal,

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it means that the power supply, PG, and clock before the reset are also normal

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We can continue to check the signals after reset to see which ones are not generated

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Reverse from each condition to see what conditions are still missing

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Check the CPU clock, reset, PG, such as PROCPWRGD, VCCST_PWRGD and other signals to see if they are normal

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You can also check the power supply of each module of the bridge

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If there are no problems with these conditions, we can try to replace the EC,

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replace the CPU power supply chip, replace the bridge or replace the CPU for testing

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to narrow down the scope of the fault

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The second fault phenomenon is that after pressing the switch, the current has a jump action

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It means that it may have already entered the self-test state,

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and has entered the soft start process

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If it is not displayed at this time, we generally rule out the BIOS first

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First flash the BIOS, and then use the diagnostic card to see if there is a jump in the code

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and if the memory has been tested

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If there is no self-test memory, we will check the working conditions of the memory,

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and then focus on the problems of PCH, CPU and EC

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If the memory has been self-checked, check to see if the graphics card has been initialized,

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plug in the screen and see if there is a screen reading action

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Like older machines, you can measure the EDID signal of the screen interface

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to judge whether there is a screen reading

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The new machine uses eDP signal, we can test the EDP_AUX signal to see if there is any screen reading action

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Include the sleep lid switch signal LID, to see if it works

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Normally it is high level, if it is low level, it will also cause no display when booting

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We also need to check whether the backlight circuit of the screen is normal

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You can also replace the screen cable, replace the screen,

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and measure whether the resistance to ground of the data line of the screen interface is normal,

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whether there is an open circuit or a short circuit,

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If these problems have been checked,

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we also need to consider the reasons for the peripherals

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Problems with external devices will also cause no display when booting

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For example, the overcurrent of the USB device, the short circuit of the touchpad, etc.,

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will cause no display when booting.

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The third type of fault is that after the power is turned on, the current jumps once or twice and then stops

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This is obviously because the memory self-test fails

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If the current jumps continuously after starting up, and the screen is about to light up,

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we will focus on checking the working conditions of the graphics card and checking the LID cover switch

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For example, the current is up to 0.559A, 0.6A, which is already relatively high

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Especially for models like 1466 and 1465,

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this current is almost close to turning on the machine

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Check the conditions of the memory

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Mainly check the main power supply of the memory, VTT power supply and VPP power supply, etc.,

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as well as the data line and address line of the memory, we measure it through the value card

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We can also test by replacing the memory, or replacing a slot

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If the CPU is pluggable, you can replace the CPU test

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Like some all-in-one machines, its CPU is pluggable

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At the same time, we can also check the working conditions of the CPU memory module

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Use an oscilloscope to measure whether there is a waveform that reads the memory

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Like the one with memory slots, there is a system management bus,

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which can measure the waveform of reading memory

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The fifth type of fault, the external connection can display,

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but the internal screen does not display

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In this case, we focus on checking the LID switch,

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and use an oscilloscope to measure whether there is a screen reading action

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Check the screen cable, replace the screen test

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You can also test whether the data line to ground value of the screen interface is normal,

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and check whether the backlight circuit is normal

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Next, we learn through two cases

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The first case is that the mainboard has been flooded,

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causing the bottom pins of the backlight driver chip to corrode

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After we disassembled the chip, we replaced the missing pins and the broken signal lines,

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and then soldered the chip back

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It can display normally after booting

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This is because there is a problem with the backlight circuit, which causes no display after booting

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The second case is also a problem with the backlight circuit

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Waterlogged machines are especially common

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There is no display when booting up, and the backlight circuit is really not repairable

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We can cut a backlight power supply circuit from another mainboard and migrate it through the way of transplanting,

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and use flying wires to make it work and provide working conditions for the backlight

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This is the result after repairing

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Ok, this is the maintenance of no display fault when starting up