lcd screen black after replaced it

You most likely have a faulty screen.

Try holding down the power and volume up buttons together. Wait until you feel it vibrate 3 times, keep holding for another 5 seconds or so.

Also check the cable whick the LCD plugs onto... make sure something hasn't been damaged.

Same problem can't find fuse diagram any where for this model every other but z3+ :(

PS it's definitely on my board not a ribbon or screen

Shine a light on your screen and look very carefully, see if it powering up it could just be the backlight fuse has blown.

In Sony Xperia Z4 Manual following steps are written to troubleshoot screen problem.

• Remove the back cover of your android device and reset the battery to make sure that the contacts are touching properly, and the phone is getting power. Then charge your phone and leave it for charging for few hours.
• If the first step fails to solve Android Black Screen Of Death issue, then take out the sim card, SD-card and battery from the phone and leave them for 5-10 seconds. Put the battery and charge it.
• If the previous step also fails, the hardware factory reset will be the last step to perform. This process will erase all the data on your android phone, but you will not be able to backup them because of the Android Black Screen Of Death. Make your phone ready for hardware factory reset by resetting the battery and taking the SD care out. You can keep the sim card in your device and close the phone.
• Now put the phone into charge to avoid any distraction in the factory reset process.
• Press and hold the Volume up, Power and Home keys to boot the phone in recovery mode. In the recovery mode, select Factory reset/ Wipe data using volume keys. Press Power key to start the hardware factory reset.