Xperia Z3 Plus - LCD is black digitiser is responding after replacemen

I have carried out an LCD replacement with OEM LCDs and initially the LCD worked perfectly, during testing phase. Upon reassembly the LCD displayed a black screen but I can still use the digitiser as I can hear interaction and sounds coming from the handset.

I have tried several different LCDs but all of them seem to behaving exactly the same.

I have replaced LCD flex and also replaced the battery and USB flex.

The Device does not get recognised by Sony Companion although I have managed to reset/repair the software several times but with no results.

I have also isolated the LCD cables with tape to avoid shorts caused by the metal bracket that separates LCD cables from USB flex etc.

The logic board appears to be fine.

What am I doing wrong.?