Backlight issues, including no backlight, dim backlight, half backlight, or iPhone won’t turn on etc., are commonly seen in iPhone repair for a repairman. Here we will introduce the repair case of iPhone 7 Plus half backlight issue due to pseudo soldering of the display connector and the related backlight circuit. Hope to enlighten you on this subject.
For mobile phone logic board repair, cosmetic inspection always comes to the first. Check the logic board carefully, there is no deformation nor signs of water damage.
Next, let’s assemble the phone and test. Get the logic board and display assembly installed. Connect the battery and press power button. The screen lights up and Apple logo appears. We can see with naked eyes that the right side of the screen is darker than the left side. Judging by this, the fault might be related to the backlight circuit.
Take apart the phone and remove the display assembly. Take out the logic board. Run diode mode measurement of backlight relevant pins on the display connector J4502. The measured value of Pin 45 is OL, which is abnormal. A normal value should be around 450.
Check with schematics, you will see the voltage outputted from the backlight IC U4601 reaches Pin 45 of J4502 by way of C4602, FL4601 and C4605. So continue to run diode mode measurement of C4602. The measured value is normal. Judging by this, the abnormal value of Pin 45 is probably caused by open-circuited condition of its relevant circuit or malfunction of the display connector J4502. Check J4502 carefully and we find that Pin 45 has been pseudo soldered.
To further confirm the faulty position, desolder the J4502 from the logic board. To desolder the connector, first stick High-Temperature Tape on components around for protection. Then apply some Paste Flux to J4502 and remove J4502 with 858D Hot Air Gun afterward.
After the removing of connector, we get access to measure the diode value of Pin 45 on the bonding pad. The measured value is normal.
As of now, we can confirm that the fault is related to J4502. We can fix the problem by replacing with a new display connector. Next, heat with 858D Hot Air Gun. Clean the bonding pad with rosin soaked Solder Wick. And clean with PCB Cleaner afterwards. Apply some Paste Flux to the bonding pad. Get a new display connector in position and solder with 858D Hot Air Gun. Next, secure the four sides with Solder Paste for successful soldering. Once done, clean with PCB Cleaner.
Now we can assemble the phone and test. Get the logic board and display assembly installed. Connect the battery and press power button to power on. The phone turns on normally. The screen is also back to normal. Fault cleared.
Warm tips: get the phone full assembled after confirmation of fault clearance.
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