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Hello everyone , So I bought a used iPhone 8 plus from ebay but when I power it on I noticed the left corner of the screen looks dim so should I buy screen replacement or could the motherboard be damaged?
This is a faulty component on the backlight circuit. It is becoming an increasing problem with the 8 plus. Usually it is a small resistor which has failed causing the screen dimming in that exact place. You will need to find a repair shop that does microsoldering. It will be a fairly cheap repair.
You can put a new screen on and test. If the screen remains half backlight, then it’s a logic board problem.
