Apple Performa 6400/180 - Manual (Page 217)

Additional Procedures 6500—Distinguishing Video Jitter from Blur - 9
6500—Distinguishing Video Jitter from
Blur
Service providers may encounter two slightly different
video symptoms on monitors connected to Power Macintosh
6500 computers. The first step in troubleshooting this
issue is to differentiate video jitter from blurry video.
There is a different solution to each of these conditions.
Video jitter affects monitors connected to models having a
225 or 250 MHz logic board. Jitter is evident at the edges of
the screen or windows and dialog boxes where the pixels
shimmer or jump.
Blurry video is seen as a fuzzy image over the entire screen
on monitors set to resolutions of 832 x 624 and higher.