Most of the time, when I see graphics issues, I just assume that it’s going to be PPU related. Take for example this unit I worked on recently. Here’s a photo from Super Mario World.
Those big chunky malformed graphics scream PPU1. But, after swapping the PPU1 chip, I got the same issue.
The diagnostic cartridge showed an interesting result, it would run the burn-in test up to DMA Memory, and then, show only a pink screen.
Some test (or tests) failed – but it was not possible to see which ones.
Finally, I pulled the CPU off this board and moved it to another board that had no graphics issues, but had corrupted controller input memory. Starting up the unit after the transplant showed similar (albeit slightly different) graphics issues on SMW and the test cartridge.
This confirmed that the CPU was indeed the issue – perhaps something with DMA – but it’s hard to say for sure.
Another one bites the dust!
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