I just replaced a severely broken 21.5 inch 2012 A1418 13,1 iMac screen with a new LCD. The original broken LCD didn't display anything....just a black screen! I don't really have any history on the machine since I bought it at auction several weeks ago with the damaged screen. The machine boots/runs fine, hooked to a alternate monitor. The newly installed LCD screen is black with no visible image even when I shine a light on it. Since it works flawlessly with the attached monitor, I think I can safely assume the problem isn't on the logic board or the GPU. Also Since the invertor is new, it shouldn't be bad. I now wonder if the lvds video display cable is damaged. Does anyone have any other ideas as to what the problem may be before I order a replacement cable?