I had the same problem, the screen would go funny in interlace modes. Just the upper half. It would shake and show corruption around the borders. Did it both on the rgb and the vga. I don't think its the 2meg agnus reason being that i have installed the indivision ecs and all corruption is gone using that. I think its more of the amber chip or maybe a capacitor issue maybe? This started over a year ago and system still running great. Here is some pics before i fix'ed with indy ecs.
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lost
