No power or boot loop .code on screen

Im trying to repair an ipad 3 ,it had no power issue would detect charger thejust flicker and say detected again . Iv tried a replacement battery replacement port , even tried moving the logic board over to a new housing . Managed to get power but if yiu switch it offit gets stuck at apple logo or gets stuck and shows random code on the screen ( white text in small on the boot screen saying nand error

) . Iv managed to restore it via itunes but still same issue .. its really confusing one