Repair iPhone 6 won't turn and no backlight failures

We received an iPhone 6 from our customer, the fault description is that the iPhone 6 won't turn on. Disassemble the iPhone to observe it, we found that the top right corner screw column of the iPhone CPU is missing, the iPhone motherboard has been dug and welded jumper wire. Pic 1



First connect iPhone motherboard to the DPS DC power supply to check the current condition, we found that the iPhone current was above 200mA, then dropped and stayed around 150mA. According to the iPhone boot current working process, we analyze that the iPhone isn't turned on when the current was above 200mA, this failure is usually caused by iPhone display and backlight circuit. Use digital multimeter to measure the grounding resistance value of the display and backlight circuit. Pic 2


The resistance value measured is normal, so we replace the iPhone display IC, but the problem still the same after replacement. Now, we need to replace the iPhone backlight IC, after replacement, we found the iPhone boot current jumps normally. Install the iPhone display assembly and test it, the iPhone can be turned on, and the backlight also is normal. However, when the iPhone came to unlock the interface, the iPhone display screen suddenly became dark and then completely black, the iPhone backlight didn't work anymore, and the iPhone boot current stays at the same value as before.

Seems it's the iPhone backlight problem, and it causes iPhone can't enter the IOS smoothly. Replace the several iPhone backlight ICs, but it is still not working. Measuring the voltage with digital multimeter, the working condition of the iPhone backlight all is normal, only the voltage of backlight boost 17V are not up to the normal value. Check iPhone by the light, we can see that the iPhone screen stuck in the boot interface.

Replacing the iPhone backlight IC is useless, so we are going to replace the iPhone backlight IC, iPhone diode tube and inductors. Pic 3



After replacement, the iPhone was normal at first, but it didn't work the second time it turned on. Check iPhone schematic diagram via WUXINJI Dongle, we found there are many wires under the screw column, which includes the wire of the iPhone backlight circuit. Pic 4



Put iPhone under the Stereo Zoom Microscope, dig the iPhone motherboard，we found the cathode wire of iPhone backlight is cracked, solder the jumper wire on it, and then apply some green UV oil. Pic 5



Connect iPhone motherboard to DC power supply to test it, the problem still the same, so it's not the problem of the board layer circuit line. Ask another colleague, he said there were another situation that would cause the iPhone no backlight, which is DWI bus from the CPU to the backlight IC and the main power supply, it is used to adjust the brightness of the backlight. We can remove the iPhone backlight and main power, and then measure the grounding value of the DWI bus, if all is normal, then need to replace the iPhone main power IC. Pic 6




After measuring the data of the DWI bus, the data tested is normal, finally we replace the iPhone power IC, and then reinstall the iPhone backlight IC. Turn on iPhone and test it, now the iPhone backlight works properly, the iPhone can be turned on smoothly, and it can enter the IOS system normally. 

TIPS: More free phone repair guides, as well as more mobile phone repair equipment and mobile phone repair kits, you can check www.vipprogrammer.com

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