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123. Small startup current working principle verification
In this video, we will mainly verify the working principle of the small power-on current

Small current when iPhone is turned on

In this video, we will mainly verify the working principle of the small power-on current

We know that the CPU lacks power supply, clock signal and reset signal,

which will lead to small current faults

Let's remove the 24M crystal oscillator first, or disconnect the line,

and observe the change of current

Let's take the iPhone X model as an example

Find the 24M crystal oscillator in the component map,

and search for its position number in the circuit diagram

After finding the crystal oscillator,

we can see that the crystal oscillator pin passes through a resistor R1011,

and then connects to the CPU

The other pin is directly connected to the CPU

After removing the resistor R1011,

let's turn it on to see if it will cause a small current

We first find the position of R1011 in the bitmap,

the resistor is below the crystal oscillator

Let's take a look at the take-off current of the iPhone X mainboard

After the switch is triggered, the current starts to jump from 50mA

Next, after we remove the resistor R1011, look at the start-up current

After the resistor is removed, we trigger the switch,

the current is only 24mA, which is half of the normal current,

which is 50mA normally

Next, we disconnect or ground the reset of the CPU, and then test it

We search for COLD_RESET in circuit diagram

The reset signal of the CPU is connected with other reset signals through a resistor R1020

Let's take a look at the position of R1020 in the physical object

It is at the bottom side of the CPU, above the USB chip

We remove the resistor R1020, and then turn on the power to test the current

After removal, we trigger the switch,

the current is only 41mA,

which is about 10mA less than the normal current

Through testing, we found that problems with the clock signal and reset signal will cause small current

If the power supply inductor of the CPU is removed or falsely soldered,

it may cause a large current

If you're interested you can test it

Ok, that's all for this video

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