Follow the steps in this guide to repair iPhone 6s plus won’t turn on problem. This guide includes logic board repair solution of the problem which is caused by the defective U4000 power supply chip.
Example:
iPhone 6S plus won’t turn on while there is a response when connecting to a computer.
Failure Phenomenon:
There is nothing displayed on the screen after turn on the iPhone 6S plus while the computer prompts for a password when iPhone 6S plus connected to it.
Maintenance Procedure:
● Disassemble the iPhone 6S plus and remove the motherboard, use the power cord to connect the DC power and power on the main board, the DC power shows the current beat normal, but nothing shown on the screen, most of these failures are caused by the abnormal power supply of the display screen.
● Use a multimeter to measure the ground impedance value of every display screen pin, no short circuit or open circuit has been found, then test the power supply of the screen display. The power supply circuit of screen display is shown in pic 2-20.
● The normal voltage of C4002 is 6V, but it’s only 2V now which is obviously lower than normal standard.
● During analyzing the problem, we find that the working conditions of the U4000 are normal, so it is estimated that the damage is caused by U4000, the problem has been solved by replacing U4000. The physical location of U4000 is shown in pic 2-21.
Pic 2-20 Display Power Supply Chip U4000 Circuit
Pic 2-21 U4000 Chip Physical Location
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