Help with Dreamcast Repair – Slow start with choppy video

[Gocha]

Hi, this console is from a friend of mine and for some reason it doesn’t work. It is an American (NTSC-U) v1 console that when turned on it tries to start but everything looks glitchy and very slow or choppy, the only thing that is normal is the audio. If given enough time the whole Dreamcast logo will appear and load to the bios menu, but it will not run games.

Here is a video of the problem:



What I know so far:
- Replacing the power supply, the drive, the fan, the controller board and/or cables with tested and working ones makes no difference. The problem Is probably on the main board.
- I tried using every part other than the main board of the console on another one and they all work.
- I can’t see any sign of damage on the main board.
- The pins on the power supply have the right voltage each.
- Sound doesn’t seem to be affected.
- Using the console with the lid opened just shows the logo and take you to the bios normally.
- The owner was using a bad voltage transformer just before it started acting weird, I suspect that might have damaged a component, but as I said before, the power supply is working fine and replacing it makes no difference.

If anyone knows what could be the reason, the failing component or what else to test I would appreciate it.

[Daydreamer]

I have a Dreamcast with the same problem, I was told it's due to the failing GPU chip.

[Gocha]

Someone said that to me as a theory, but I have no way to test it other than replacing the GPU with another one. As far as I know no one has made a post or video about solving it.