In my phone fixing experience, if the display isn’t physically damaged from impact pressure or heat; it’s always the ribbon cable, you tried reseating it already so can you get your hands on another ribbon? If so and you have the same exact pattern of green lines then maybe the connector is the issue, probably a cold/cracked solder joint if the connector were bad
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Ribbon cables can also be a pain to seat correctly, no harm in giving it a couple more shots
In my phone fixing experience, if the display isn’t physically damaged from impact pressure or heat; it’s always the ribbon cable, you tried reseating it already so can you get your hands on another ribbon? If so and you have the same exact pattern of green lines then maybe the connector is the issue, probably a cold/cracked solder joint if the connector were bad