iPod touch 4 goes white screen when not plugged in on charge

I've replaced a rear case on a iPod Touch 4th Gen and when I've assembled it back together the screen started making funny white lines and then tremble for a few seconds. After a few seconds, the whole screen was white. The thing is, when I plug it in the wall charger it works fine, no white lines, no nothing, only when I disconnect from charger it starts to flicker and turn white screen.

Any ideea what might cause this ? I tried new screen, new battery, restore, clean lcd connector, put back the old rear case.

via iLounge Forums http://forums.ilounge.com/ipod-touch/278142-ipod-touch-4-goes-white-screen-when-not-plugged-charge.html