By Katie Marsal

Published: 11:45 AM EST

Illustrating the scope of a flaw in older NVIDIA graphics chipsets, Apple has extended its special warranty on the GeForce 8600M GT in certain MacBook Pros from two to three years.

Those visiting Apple's support page for the video corruption and failure issues suffered by this portable generation have noticed that Apple has quietly added an extra year to its coverage, giving owners of the affected MacBook Pros free replacements as late as September 2011 depending on the date of purchase.

Apple hasn't explained why it's granting the extra time but reiterates the stance it held when it first made exceptions. After NVIDIA first tried to convince Apple that its 8600M GT parts weren't affected by a graphics failure problem harming computers from HP and other vendors, an Apple-led investigation found otherwise.

The issue is believed to be an inherent defect in all GeForce 8400M and 8600M graphics processors based on NVIDIA's choice of non-eutectic (varied melting point) contact material in the graphics chips. As the cores regularly hit a temperature that damages the contacts between the chip dies and the package they rest in, the parts are gradually worn down to where contacts break and produce either obvious visual glitches or no visuals at all.

An uproar from both owners of MacBook Pros and other affected notebooks prompted a lawsuit just this month that accused NVIDIA of inadequate design and asked it to compensate users for the cost of repairing these systems.

Claims exist that the GeForce 9600M in the unibody MacBook Pro may share the same material that led to the failures, but NVIDIA has denied this and says the material is the same used in a large range of chips that have been working properly. The GeForce 9400M integrated chipset uses a noticeably different material and isn't believed to be at risk.