Some PC graphic cards do not output 1280 x 720p correctly. There appear to be two variants of this resolution, one with the correct number of lines per frame (750), and one with the incorrect number (746). It would seem that this is due to some graphic cards being unable to generate the correct pixel clock frequency (74.25MHz for 60Hz and 74.1758MHz for 59.94Hz).

This then makes it difficult for a CORIO2 unit with Genlock / Lock&Mix to lock on to the PC's incorrect source. However, by changing the 'Lines/f' value in 'Adjust resolutions' for that resolution (set 'Advanced menus=On' first) from 750 to 746, you can then lock to that source. However, this would then make that CORIO2's output wrong - on a C2-7200 with HD-SDI out, you would no longer get an HD-SDI output.

It also makes it impossible for the 1T-C2-520 DVI-I to SDI convertor to correctly convert this to HD-SDI. There is no solution for this issue, other than to use a graphic card with the correctly timed output.