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I connected a new lcd for my iphone 6 plus i changed the home button with my old lcd and started up my iphone. But my screen went red and it stayed red. Does anybody why

Turn off your phone, lift the screen, then disconnect the battery. After your battery is disconnected, remove the LCD connectors and clean them with 99% IPA. Blow them dry with compressed air to knock out anything that could have floated in there. Reconnect the screen, hook up the battery and turn the phone back on. If you still have a red screen, you probably have a bad LCD.

A red screen is typically related to a bad front camera flex. Unplug the battery, then unplug the front camera flex and home button flex. Reconnect the battery and try to boot the phone with them unplugged. If it boots fine, then repeat the process adding the camera flex and home flex 1 at a time to determine for sure if which it is that is causing the issue.