First, let’s take a look at the power supply circuit for the touch and display parts. Below is the power supply circuit diagram for the touch IC-U2401 and U2402.
U2401 has two power supplies: one is 1.8V from the power supply IC-U1202, which can be measured at the capacitor C2403, and the other is 5.1V from U1501.
The touch IC-U2402 has three power supplies: PP1V8 is 1.8V from the power supply IC-U1202, PN5V7_SAGE_AVDDN is -5.7V from U1501, and PP5V7_SAGE_AVDDN is +5.7V from U1501. Now let’s look at the power supply circuit for the display.
The three backlight control signals output from U1502 pass through inductors FL2024, FL2025, and FL2026 to the display interface J2019. These three inductors are prone to corrosion, causing display without backlight, and can be shorted.
The PP1V8 from the power supply IC and the PN5V7 and PP5V7 from U1501 pass through inductors FL2027, FL2061, and FL2037 to the display interface J2019. These three inductors are prone to corrosion, causing backlight without display, and can be shorted.
The display and touch screen are powered by U1501, which is responsible for powering both the touch screen and display. It has a high working current and is very prone to failure. Especially for devices that have been exposed to water, it can easily corrode and damage or short circuit, leading to power leakage, high current without booting, or normal current when booting without screen, and high current when booting with the display. The inductor L1519 is also prone to corrosion and damage, causing U1501 to not function properly, resulting in no display. If one of the outputs is abnormal, it can also cause display without touch or display with stripes.
The backlight IC-U1502 is also in a high voltage and high current working state, making it very easy to damage, causing display without backlight. Since PP_VCC_MAIN directly supplies power here, damage to this IC can also cause power leakage or high current without booting. The inductor L1503 and diode D1501 are prone to damage, causing high current without backlight when the screen is installed and powered on.
If the touch is partially unresponsive, reinstall or replace the touch IC-U2401 and U2402. Additionally, if the touch part is not functioning properly, it can cause display with stripes and complete touch failure. The repair process is as follows: install the screen and power on, check at capacitor C2403 for 1.8V, check at capacitor C2402 for 5.1V voltage, check at C2415 for 1.8V, and check at C2414 and C2409 for +5.7V and -5.7V. If there is no 5.1V, +5.7V, or -5.7V, it indicates that U1501 is not functioning properly. Check the power supply PP_VCC_MAIN for U1501 to see if it is normal (the normal voltage can be measured at C1547 as 3.7V). Check if the inductor L1519 is damaged or open circuit. If both PP_VCC_MAIN and the inductor L1519 are normal, then replace U1501, as shown in the figure below:
iPhone6 has two versions: iPhone6 and iPhone6 plus. The biggest difference between these two models is that the iPhone6 plus has a larger screen. The original backlight boost circuit is already overloaded, so the iPhone6 plus uses two sets of backlight, with two backlight boost ICs, namely U1502 and U1580, while the iPhone6 has only U1502. The positions of the display power supply ICs are also slightly different, as shown in the figure below:
The two backlight boost outputs of the iPhone6 plus are 17V voltage that go to pins 2 and 3 of the display interface on the lower right side. When the screen is installed and powered on, the voltage can be measured at the test points. The backlight boost IC output voltage of the iPhone6 is sent to pin 1 of the lower right side of the display interface, which can also be measured at the test points when the screen is installed and powered on.
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