Front camera not working after screen replacement on Ipad 4

Hi.

I Have repaired at least 30+Ipad 4's with out this problem occurring. Anyways I had 6 Ipad 4's from a client yesterday for screen replacements. Before adhering the screen down I was doing the usual checks and on one of the Ipads the front facing camera was not working. Just a black screen as if the shutter wasn't opening. Rear camera works fine. I checked the board and can find no nicks where I may of cut into it.

I Havnt done much trouble shooting except for a hard reset.

I do have a new camera with me.

Any other idea's or suggestions?

Thanks