Chosen Solution
Ok so we sold a used iPhoen 6 Plus to a customer, they brought it back after a few weeks with the device not powering on at all. Did some diagnostics and found that it came on with a new screen. So we replaced it. A few weeks go by and it’s back with the same issue, it will turn on with a new screen, the other screen we took off works fine on another iPhone 6 Plus but not this one. 3rd time so I know it has to be specific to this device.
Maybe the LCD FPC connector on the logic board needs to be replaced if physically damaged? Maybe a no backlight issue? You will need to check the screen with a flashlight when turning it on for dim apple logo.
