Iphone 4 display lights up when locked?

My iphone 4 lights up every 19 seconds and the strange thing is that is locked.

No message, just lights up a few seconds than goes back to black. 19 seconds later it lights up again?

The phone doesnt light up when connected to itunes or charging?

I've tried restore, update and also changed both battery and dick connector.

Also tried cleaning the mainboard with alcohol in case it has been wet. (The markings inside where white)

Anyone has a bright idea what this could be?

Googled alot and it seems im not the only one with this problem.

(I hope you can understand my english. Swedish is my language)