iPad Air Digitizer / Touch Screen not working

I have been trying to repair an iPad Air screen for a friend.

The touch was not working at all , but the home and power buttons were working fine. Firstly I tried doing a factory restore but the issue still remained; no touch response at all. I then tried opening it up to test for loose connections, I unplugged all connections relating to the digitizer and replaced them - this still did not solve the issue.

I have now tried buying a new digitizer, though not an official one, and after fitting it the same problem is still occurring - no touch response at all.

So is this a motherboard issue, or am I missing something? Any help and guidance would be appreciated as this is not something I had previously done before.

Thanks

Marty