Could this be a Screen Fault or deeper?

This S5 Came into the shop, normal thing, turning on but screen unresponsive. So ordered another Screen from my normal supplier. After receiving screen started the change over

Full picture:

As I'm sure we all do when changing these screens

Changed Charge port

Changed Screen

Tested:

And all that I got was a screen full of pixels (as in pic). checked connector, cables

never had this with an S5 before, in fact any screen. So thought I would ask the Girls and Guys here

Regards