It would make more sense for those signals to be integrated
AFTER your mod for RF output. I agree that it's most likely
a "mechanical" issue like a solder bridge or hookup wire short
than a bad chip.

wrote:

Also, what makes me think that some chip is damaged, is that the
standard analog (RF) video output has the same problem as the newly
modded RGB output. Since the RF video output seems to be routed
*before* the mod I made, the problem must be even before the RF
circuit. That's why I fear that the memory is damaged.