your iphone starts but its display remain blank. try to call on your iphone number does it ring or not. if your iphone ring then we can say that display remain blank but iphone is working and problem with your new lcd.
also try to connect your iphone to computer. does iphone recognize by computer or not.
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here is more detail troubleshooting for iphone ipad wont turn on black screen.
Your lcd may not compatible with your iphone.
your iphone starts but its display remain blank. try to call on your iphone number does it ring or not. if your iphone ring then we can say that display remain blank but iphone is working and problem with your new lcd.
also try to connect your iphone to computer. does iphone recognize by computer or not.
http://ipodtips-tricks.blogspot.in/2016/07/ipod-would-not-turn-on-black-screen.html