metrocctv

Hi all, Have been stumped by this issue for a while now and wanted to ask for your opinions. We are using cat 5 and active baluns. the baluns use 3 pairs for power and 1 pair for video. checked voltage at end of cable run and is reading 12.9v at this particular run. The cameras that we have purchased for the job are the ICU 920XI-36-ADJ I think they are manufactured by a company in korea called Lacie, but have been re-badged by the australian distributor. When i plug this camera in on a run anything longer than 10 meters we get no video signal. shorter than 10 meters is fine. Any other camera that we put on the same run (including cameras drawing much higher current) works fine, just this particular camera is having this issue. We have tried, different baluns, local power, different camera (same model), different model cameras (works fine). if we plug an lcd into the camera but still get power from the balun, we get a picture. so im assumuing that it has somthing to do with pair used for video, but all other cameras work, so i am sort of stuck at the moment. any suggestions as to what it might be??