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Hello everyone, today we will learn how to repair the power down failure of the Apple laptop

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Power down means that after pressing the switch,

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the mainboard enters the power-on state from the standby state,

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and the current rises accordingly, and then automatically shuts down,

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which is called power down

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Common power down faults are divided into the following types

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The first is that the standby condition of the chipset is not normal

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For example, the reset signal of RTC is normally 3.3V high level,

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and the minimum cannot be lower than 2V

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If it is exactly 2V, it is in a critical state and will cause power down at any time

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This is a fault that has been repaired more often.

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When encountering this kind of problem,

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measure each standby condition of the chipset one by one to see if they have normal voltage values

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Second, we need to measure the conduction condition of the isolation tube

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to eliminate the power-down fault caused by the false common point

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The second fault, the standby condition of the EC is not normal

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For example, PP3V3_S5_AVREF_SMC, if the power supply is not normal,

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it will also cause power down when booting

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Therefore, it is necessary to carefully measure whether the EC's standby power supply, clock, reset,

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and switch signals and LID signals are normal.

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The third fault is power failure caused by abnormal temperature control circuit

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This kind of fault can search for "THERMTRIP" signal in the circuit diagram

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and check whether it is normal

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Generally, this signal is connected to the temperature control circuit, normally it is high level,

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if it is low, it may cause power failure

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The voltage is insufficient after starting up,

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and some power supplies have not been successfully turned on

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For example, lack of CPU power supply after booting, or lack of bus power supply

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It will cause power down, which is a power down due to lack of voltage.

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You can use the dual channel of the oscilloscope to compare the waveforms of each power supply

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to see which power supply has not been generated before the power failure

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Compare the SLP_S3# signal to see which power supply drops earlier than the SLP_S3# signal,

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and the power supply that drops first is problematic

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If SLP_S3# falls first, then there is a problem with the bridge or chipset

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After receiving the switch signal, the chipset sends out SLP_S5#, SLP_S4#, SLP_S3#

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to turn on the power supply of the following channels

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Within the specified time, if some power supply is not successfully turned on,

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the chipset will automatically turn off the SLP_S*# signal to cause power failure

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This is a power failure

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There is also a power failure during the soft startup process,

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which has nothing to do with the hard start

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There is no problem with the power supply, clock, and reset signals

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The CPU has been working, and the BIOS has been read,

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and the self-test of the entire mainboard is performed

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During the self-test, if a problem is detected with a device,

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it will cause a power down

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Of course, there are also power failures caused by the BIOS itself

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For example, there is a problem with the BIOS itself,

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which causes failures during the self-test of each device, causing the self-test to fail

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During the self-test process, when each device is self-tested,

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if a certain device fails the self-test, it will cause power failure

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In this case, we can try to flash the BIOS first,

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eliminate the cause of the peripherals, and finally try to replace the chipset or EC

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The last type of fault is that after entering the system,

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the power is cut off from time to time during normal use

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In this case, we need to rule out the cause of the external device or the temperature control circuit

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You can also try to replace the memory, replace the BIOS,

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or reinstall the system

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Change the hard disk, reinstall the system and test,

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eliminate the cause of the system and software, and then consider to reball the chipset or EC

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Next, let's look at a case

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For example, Apple A1465, power down at about 0.7A

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When the power is turned on to 0.7A, the power is cut off,

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and it can be triggered repeatedly after the power is off

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In this case, it is generally necessary to consider Apple's common problem,

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which is the power supply of EC's PP3V3_S5_AVREF_SMC

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If the power supply is not normal, it will cause the power down at about 0.7A

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After measuring we found that there is no voltage of this power supply

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After measuring the impedance, I found that its resistance value is only 0.0053,

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which is quite low, and it is obviously short circuited

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In this case, either the chip that outputs the power supply is short-circuited,

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or there is a problem with the capacitor at the output end,

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or there is a problem with the EC itself

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Let's start with the easy and then the difficult, first eliminate the filter capacitor

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After replacing the filter capacitor, the problem was fixed

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This capacitor has been replaced

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After the replacement, it can be turned on and it can enter the system normally

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OK, this is a repair for a power down