We’ve received this iPhone 6s from Tanzania, East Africa and customer tried to replace LCD screen and unfortunately he damaged the LCD FPC connector and backlight filter on this iPhone6s. so we’ve replaced the LCD FPC connector and also replaced the backlight filter with new one and after that phone starts working without any issue.
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iPhone 6 Full Backlight Circuit Repair ( Capacitors, Diode, Driver IC, Coil)
Repairing iPad Pro 12.9 with No Display or Touch Issues After Screen Replacement
iPhone 6S Backlight Circuit Repair – Coils, Diodes, Capacitor