Big white horizontal bars on screen

hello,

recently i worked on u2 ic on an iphone 6s and and when i tried to turn it on,my power supply stopped at 0.03amps. then i couldn't work on it for few days and today i tried to turn it on again. suddenly it turned on normally and after 2,3 seconds from apple logo,big white horizontal lines (nearly 1 inch) appears and it goes up to down and keep repeating.i have no idea what i’ve done wrong.i’m new to microsoldering and done only 3 u2 replacement so far.(all went smoothly).this phone had a battery draining issue and heating from bottom initially.so i guessed its a faulty u2 without testing voltages and proceed with the u2 replacement.any advice would be highly appreciated.thank you for your time.