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Step 5 of short sircuit repairing for iPhone standby circuit

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burning detection

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What is burning detection?

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In a short-circuit line,

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the external power supply is used to supply power to the short-circuit line

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The greater the current we provide,

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the more obvious the component damage will be

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so as to quickly find the damaged component

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After we smoke the short-circuit components with rosin,

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we will start to detect

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There are two burning detection methods,

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the first is to use an adjustable power supply,

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and the second is to use a burning battery

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In the first method, the voltage is adjusted to about 4V,

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and the current is adjusted to the maximum

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Then the positive pole of the power supply first touches the short circuit,

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and the negative pole goes to ground

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After waiting for three to four seconds,

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look at the rosin-smoked components to see if they have melted

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If there is melting, just replace the melted component

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Here are some notes

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Hold the tweezer with clips when detecting,

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and choose tweezers with thicker pointed tips

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If the tip is too thin, it may be burned

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Or we can use multimeter test pen instead

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Now, let's get started

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We first adjust the adjustable power supply to about 4V and the current to 5A

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and the current to 5A

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We clamp the tweezer with the positive pole of the adjustable power supply

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The positive pole first touches the short circuit,

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and the negative pole is grounded

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When we contact, choose a position that is easy to touch,

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and do not choose the position in the corner,

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because it is easy to cause other components to be burned out

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The positive pole first touches the short circuit,

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and the negative pole is grounded

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After waiting for three to four seconds,

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look at the rosin-smoked components to see if they have melted

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Which position has the rosin melted first,

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indicating which component is damaged

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We can replace it directly

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If the fault cannot be eliminated when burning detection with the adjustable power supply,

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we will use the battery to operate

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How to operate? Let's take a look

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In this method, the positive pole first touches the short circuit,

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and the negative pole needs to touch the ground

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After two or three touches, we can observe

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whether the rosin-smoked components of the mainboard are melted

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If there is melting, it means that the components are damaged

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Why do we need to touch the ground in this method?

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Because the current of the burning battery is relatively large,

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if we press the twizzer on it for a long time,

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the board cannot stand such a large current,

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which will cause it to be burned out

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In these two methods, why are the positive pole connected first

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and the negative pole grounded?

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Because, if the negative pole is in good contact first,

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the current will be very large

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when the positive pole contacts the short-circuit line,

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and the components at the contact position may be damaged

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If the negative pole is in contact first,

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and the positive pole touches the short-circuit fault point,

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you will find that the rosin will melt first wherever we click

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However, the melting does not mean that the component is damaged

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It is caused by the high current when it is touched

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In fact, the mainboard damage may be caused by

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the damage to this capacitor