Wii U unit powers on but no AV output - any ideas?

I have just purchased a faulty premium Wii U. It has a broken LCD which I have done before so that's not an issue. However, There is no AV output from the unit either.

Has any one experienced this problem and traced a fault?

Do these units brick and is there any know DIY fixes?

Is there a restore to factory settings fix?

Is the AV processor a problem on these units?

Could it be locked to HDMI like a PS3? (I only have AV available right now)

Most grateful for any and all constructive help - Dan :)