How To Solve iPhone X Voltage Jumping Issue

Today, We getting the iPhone X main board to test, we observe the current value repeatedly jumps between 0mA and 50mA on DC power supply, and it is different from the normal booting current. Next, test whether the power supply of every circuit is normal. PP_VDD_MAIN is measured 4.2V; PP_VDD_BOOST measured is 4.2V. PP1V8-ALWAYS is 1.8V, all the values are normal. But when testing PP1V1_S2, PP0V8_SOC_FIXED_S1, PP1V8_S2 and other circuit voltage that output by power chip U2700 voltage are jumping constantly. According to previous experience, voltage jump is usually caused by a power supply circuit of U2700 output. Measured with digital multimeter, there is no short circuit was found for the dipole value of all power supply to ground.

We repaired iPhone 7P before and know that if crystal oscillator is false welding can also cause voltage jumping, And if iPhone CPU power supply is abnormal also can cause voltage jumping. Check the crystal oscillator we find no problem, then check the CPU power supply! As shown in iPhone schemtic diagram 14-3-1 and 14-3-2, there are three ways of power supply, not only directly into the CPU, but also through the small resistance or inductance into the CPU, the three voltage are PP1V2_SOC, PP0V8_SOC_FIXED_S1, PP1V8_IO. 

14-3-1

14-3-2

Testing the 3 power supply one by one, when the FL1092 inductor of PP1V8_IO is measured, one end is 1.8V while the other end is 0V.

14-3-3

Testing the end without voltage to the ground dipole value is 490, the normal is about 280. Then testing the inductor's noumenon value is very large, indicating the iPhone X inductor is damaged, so we replace a new inductor, the fault is repaired well.

Later, it was analyzed that the PP1V8_IO was renamed as PP1V8_XTAL after inductance FL1092, which was supplied to the CPU crystal module. It also verified that the voltage jump of iPhone X and the voltage jump of 7P before were actually the same thing. Hope this iPhone X repair case will help you.



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