For those trying to check for dead pixel before buying it in the shop.
I found out something when I was playing with my 818pro.
When the unit is off, hold down the power and camera button all at once for a few seconds.
There'll be a screen showing a spectrum of colors for you to check the screen out.
I don't know if it appllies to the rest of the Dopod family.
Hope this helps. Cheers.....