[damen]

Have you tried swapping the 6AQ5 video output tube with one of the other 2 6AQ5s in the set? I don't think your voltage or resistance measurements are so far off as to cause this problem. The chassis uses an "extra" video amp stage, that why the video is fed into the grid of the CRT instead of the more common cathode connection. Is your video source signal negative or positive? Pins 1 and 7 are tied together inside the tube, usually only one socket connection is used. If you check voltage or resistance with the tube out of the socket you'll probably get very different readings on them.