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Short circuit repair experience for iPhone standby circuit

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If the short circuit current is 5A,

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the main power supply capacitor is generally damaged

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If the short circuit current is around 1A,

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most of the iPhone 7 and above models are short-circuited by the boost power supply

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If the mainboard has been repaired or the chip has been soldered,

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there is a short circuit fault,

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usually because the chip is damaged,

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or the chip is not soldered well,

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the pads are connected by the tin,

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or it may be that the temperature is too high during soldering,

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the tin extrusion happens on the components around the chip and causes the short circuit

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Next, we can take a look at this phenomenon of tin extrusion

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For example, when we solder this chip,

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improper temperature control during disassembly and assembly

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may cause the tin extrusion on the nearby chips

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There are many small tin balls next to the chip,

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which basically proves that the tin extrusion happened on the chip

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After the tin explosion,

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the tin inside the chip may be connected together, which may cause a short circuit

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For example, like this,

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it is the pad after we remove the tin-extruded components or the not well soldered chip

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In the upper left corner of this picture,

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we can find that many tin dots have been connected together

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If it is the short circuit between the power supply and the ground wire,

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we cannot detect it in the burning detection

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Because when it is used for grounding,

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the tin block is relatively large and can withstand large currents

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At this time, you will find that

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it is the whole mainboard that heats up during the burning detection