Dreamcast Weird Video Issue

[demianariel]

Can anyone help me figure out what the hell is wrong with this thing?

http://www.youtube.com/watch?v=XJoKsyZrikw

-Bad GPU?
-Bad Capacitors?
-Bad PSU?
-Bad Video Memory modules?
-All of the above
-I don´t care!

[Jenkins]

Do you use a VGA box / cable?

[Raen]

Most probably, the GPU section of the motherboard went kaput.

If you have a 2nd working DC, swap their boards and try to isolate the problem to a specific piece.

I did this on a non-working DC and found out that its PSU was dead (both the fuse and some capacitor), the controller board was dead and the MB had a similar graphical issue similar to yours.
While the PSU fuse and any capacitor can be easily replaced, you most probably can say good-bye to a damaged motherboard.