Apple Performa 6400/180 - Manual (Page 80)

Troubleshooting Symptom Charts/Video - 6
Video
Pixels shimmer at
edge of screen, dialog
boxes, or windows.
If Power Macintosh 6500 serial number falls within the range
from XB708xxxxx to XB719xxxxx, replace the logic board with a
reworked logic board (P/N 661-1322 for 225 MHz,
P/N 661-1332 for 250 MHz). To identify a reworked logic
board, see Additional Procedures chapter.
Poor video output
(misaligned or
skewed video, low
brightness,
blurriness, etc.)
In Macintosh 6500 Monitors and Sound Control Panel, make sure
resolution is set to 1152 x 870 or lower. See chart in Basics
chapter for supported resolutions.