XZ3 hardware problem (Advice Needed)

Hi all my problem is i bought my Z3 off ebay it had a faulty screen. The screen is not displaying anything so i bought a new screen fitted it but its still the same so bought another thinking it was the part but its still the same. So i need some advice wether its the zif on the board thats faulty or the flex ribbon. the zif connector looks to be ok. And the back light still works and i can hear the boot sounds and notifacations. I just don't want to keep buying parts willy nilly