Chosen Solution
I bought a iPhone 6s with a broken screen and I changed it with a good quality new one . I factory reset it and restored it through my computer . When I click the lock button it sometimes does display the screen properly and the touchscreen works when testing it , but when I lock it again and try to unlock it the backlight only turns on and the screen displays no image . I have tried another two screens for the 6s which work with no issues on other 6s phone I have repaired but the same problem occurs. This has never happened to me before and I’m not sure what to do now , I hope you guys can help out here, thanks .
If I understand correctly, you don’t really know if this phone worked properly before you bought it. It is possible that the LCD drive circuit is damaged. This could be caused by impacts/drops, water damage or prior repair attempts. Because you have tried 2 known-good screens, I would suspect the problem is on the logic board. Can you tell us more about the history of this device?
