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iPhone startup high current

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In this lesson, we mainly explain the maintenance process of large current after startup

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Maintenance process Step 4

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If the above conventional methods can not troubleshoot,

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that is the mainboard has a problem

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At this point, we can measure the diode value

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of all the LDO power supplied by the power supply output

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In the previous lesson,

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we talked about the LDO power supply as a low current power supply

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So when it shorts out, it causes the trigger current to be too high

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We usually test the LDO power supply first

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Let's take iPhone 12 as an example

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to measure the LDO power supply of the IC output of the power supply

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We first find the power supply IC in the component map,

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and then find the main power supply in the bitmap

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Then jump to the schematic and locate the pin of the power identifier LDO

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This power supply refers to LDO power supply,

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whose current is relatively small,

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such as 200mA, 250mA and 50mA

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Select the name, right click, click Find bitmap signal

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These yellow dots are the measuring points

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We find the measuring points on the physical picture,

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the red marker is grounded,

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and the black marker is used to measure

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Measured a value of 515, the normal value is about 500

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We don't need to test the power on this hard drive

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This current is relatively large,

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it short circuit will lead to a large startup current

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Below, we measure the power supply PP3V0_S2,

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we could measure the position of the yellow point in the bitmap

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This power supply is to the USB chip power,

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U9300 is USB

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The multimeter is switched to the diode gear,

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the red marker is grounded, and the black marker is measured

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The measured value is 389,

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indicating that the power supply is no problem,

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because the normal value is more than 300

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If it comes out as 0, that means there's a short circuit in the power supply

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Let's remove the capacitor first

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If it doesn鈥檛 work, we may need to replace the USB chip

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Like the power supply of LDO, we need to measure it

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When measured, if the value is 0,

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it means that the power supply is short circuited

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If the LDO power supply is short-circuited,

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the connected capacitor is generally broken,

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and the possibility of chip damage is relatively low

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Step 5 of the maintenance process

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If we measure the LDO power supply without short circuit,

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like this situation is more difficult to fix

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It may be caused by a short circuit in BUCK power supply

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This short circuit is not a complete short circuit

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It is a slightly short circuit

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Because if there's a complete short circuit,

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it will lead to large startup current

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High startup current maintenance experience

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If the USB chip of iPhone is damaged, the startup current is high

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We can just remove the chip

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After removal, if the current returns to normal,

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it indicates that the USB chip is damaged

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We just need to replace the USB chip

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If the chip is removed and not installed,

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it will lead to the white Apple and restart

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If this happens, we just need to solder the USB chip on

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This is the end of the maintenance process for excessively large startup current