Apple has identified an issue with the video DRAM chips used on some Pentium 166MHz PC Compatibility Cards and has corrected this in manufacturing and in service.
Identification1. System exhibits random video corruption on the screen, as described above.
2. Video DRAM chips at locations U7, U8, U16, and/or U17 on the card (above the PCI bus connector) are marked with the numbers 424260.
Solution
Customers who experience this issue should have their PC Compatibility Card replaced under the Apple One-Year Limited Warranty.