i need some assistance repairing a monitor. problem i have is that i have a single blueish vertical line on one side of my display. i have opened the monitor and i have 4 video cables. L1, L2, L3, L4. once i remove L4 i get a white screen(no blue line) which i think is disconnecting the main board. l4 connector is the only one that is black. so i think the line is from the mainboard signal rather than a faulty display panel? any ideas?? thanks!