It wasn't long ago we were troubleshooting a regular DK that would come up with only a RED screen..... it would play "blind", just only a red screen. (no image)
I only helped troubleshoot it, wasn't in on the repair, but I believe they just swapped out one board. (I presume the video processing side of things)
But the point being it was the board set.
(just kinda confirming what you already figured out)