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Hello everyone, today we are going to learn how to repair the failure to turn on of the Apple laptop

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What is the failure to turn on?

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It means when we plug in the power cord and press the switch,

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there is no current jump, and the CPU fan does not turn

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First of all, let's take a look at the boot circuit of this mainboard without T2 security chip

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Before starting up, the EC must meet the standby conditions,

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detect the insertion of the adapter,

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the switch signal and the sleep switch signal must be in high level,

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and the standby conditions of this chipset must be all normal,

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and the switch signal sent by the EC to the PCH to be high level

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When these conditions are normal, we press the switch,

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a jump of "high --> low --> high" will be generated and sent to EC

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EC delays to send a "high --> low --> high" jump pulse to PCH

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PCH will send out SLP_S5#, SLP_S4#, SLP_S3#, etc. in sequence to turn on the subsequent power supplies

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Usually SLP_S5# is to turn on the USB power supply

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SLP_S4# is generally to turn on the memory power supply

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SLP_S3# will turn on the voltage required by the S0 state

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These signals are normal in high level, all 3.3V

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The standby condition of the EC refers to its standby power supply, clock, reset, and its program

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Apple's EC comes with its own program, its clock is a 12MHz crystal oscillator,

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and its reset is SMC_RESET_L

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The detection signal of the adapter mostly refers to the middle pin of Apple, the SYS_ONEWIRE bus

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Next, let's take a look at the boot circuit with the T2 chip

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First, the Type-C adapter needs to complete the step-up,

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the voltage of the common point must be normal, and the power chip must be powered

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After the power chip has power supply, the switch pin must be high level,

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and the LID signal cannot be low

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When we press the switch, the switch signal is directly sent to the PCH by the power chip

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When the PCH receives the switch signal after the 10 standby conditions are normal,

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it will send out SLP_S*# signals

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At the same time, it will also communicate with the T2 chip through the eSPI bus

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The T2 chip will communicate with the power supply chip through the I2C bus,

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and control the power supply chip to output various power supplies

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In this process, the power supply required by the chipset is provided by the power chip,

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and the working conditions of T2 are also provided by the power chip.

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Let's look at two cases

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An A1707 Apple laptop cannot be turned on when it arrives

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After confirmation, it is indeed unable to boot

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After taking out the mainboard, visual inspection shows that there is no obvious water ingress on the board,

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and the appearance is not bad

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The characteristic of Apple is to generate PP3V3_G3H first to provide standby power for EC

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After the EC standby power supply is normal,

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it will control and generate the common point voltage

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After actual measurement, the common point voltage is normal

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When checking the standby condition of the EC,

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it was found that the reset signal had no power.

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The reset signal of the EC is sent by the charging chip, the external name is SMC_RESET_L,

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and it is sent to the RST pin of the EC

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Then I measured the resistance and there was no electricity

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Because the power chip and EC are both packaged in BGA,

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the only test point is this resistor

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After we disconnected the resistor, we found that there was no electricity at both ends

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So we judge that there is a problem with the charging chip

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After replacing the U7000 charging chip, the fault is fixed

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This is due to the lack of response to pressing the switch due to insufficient EC standby conditions

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We usually encounter failures that cannot be turned on,

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and we must first check the external devices

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Because some external devices are not normal, it will also cause the machine to fail to boot

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For example, if the network card is short-circuited or the touchpad is short-circuited,

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it will lower the standby voltage and cause the computer to fail to boot

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Some keyboards have switch buttons on them

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When the keyboard is damaged, there is no response when pressing the switch

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In addition, we need to observe the standby current

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to see if the machine current is too large and whether there is a short circuit.

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Compared with the standby current of the normal mainboard,

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if the standby current is too high, there is usually a problem with the standby circuit

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After checking the cause of the peripherals,

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we can follow the steps below to detect them one by one

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First measure the voltage of the common point of the protective isolation circuit to see if it is normal

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Then check the standby conditions of EC, power chip and T2

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If there is an exception, we track down its source

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Also check whether there is a high level on the power switch button and the sleep cover switch

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After pressing the switch, does the EC send a "high --> low --> high" jump pulse to the chipset?

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The switching signal sent by EC to the bridge is also a fault entry point

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If it is not sent out, we can lock the fault in the EC part

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If sent, we have to check the standby condition of the bridge

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If the standby condition of the bridge is met and the switch signal is received,

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but the machine still cannot be turned on, there is usually a problem with the bridge

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Next we have to check the various standby conditions of the bridge

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If conditions are abnormal, we're going to track down its source

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If the condition is normal, it will send out SLP_S*# signals to turn on the power supply of each channel

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Test whether each SLP_S*# signal has been generated normally

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If the conditions are normal,

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we will check whether each power supply signal in the power-on circuit is disconnected

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For example, switch into EC, or switch into power chip

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Is the switch signal from the EC to the bridge disconnected?

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Are the 10 standby conditions of the bridge really sent to the pins of the bridge?

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Check whether the ESPI bus and I2C bus are disconnected

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We have to judge each of these

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Well, this is how to repair the failure to turn on