Sequoia C256 Ultra Sound

Hello. I have a Sequoia C256 were the EKG data line turned yellow instead of the normal blue. The longer the system stays powered up, the more artifacts grow, always starting with the EKG data and spreading upward throughout the display back ground. The entire background turns blue and flickers. The system will be powered down for a period of time and the back ground goes back to normal, except the EKG data line stays yellow. The IOV2 video board has been replaced and all boards re-seated. The basic hardware test all passes, but I can see flickering throughout the display during the hardware testing. Can this be a monitor issue? Thanks for any leads.