My problem was related to a faulty memory chip keeping certain lines low. I replaced them by taking them from an old mac II card.

Click to expand...

There are so many different IC's in the video circuit...

Here are the schematics of the video circuit for an SE/30 logic board. I'm surprised that it is this complicated for B&W machine.



I'm going to replace the 2 video memory chips. I doubt it will solve the problem since the checkerboard pattern is static and identical every time. I would expect a random pattern with a bad video chip.

However it's worth a try: I'm going to dig in my old Mac II video cards

Thanks,

Nico