Apple late last week said it would repair at no charge MacBook Pros where the Nvidia GPU has failed, or fails within two years from the purchase date.

An investigation by Apple shows some MacBook Pros may have faulty Nvidia graphics processors after all, despite Nvidia's earlier assurances to the contrary.

Problem signs include distorted or scrambled video, or no video on the screen though the computer is turned on. Models that might be affected are 15-inch and 17-inch MacBook Pros with Nvidia GeForce 8600M GT graphics processors. The computers were made between May 2007 and September 2008.

A few months ago, Nvidia acknowledged that a packaging defect had led to a graphics chip problem that affected some notebook computers, including those made by Dell and Hewlett-Packard.

The chipmaker said in July it was taking a one-time charge of US$150 million to US$200 million to cover expenses relating to the glitch.

In a statementabout the problem, Apple said that back in July "Nvidia assured Apple that Mac computers with these graphics processors were not affected." But the computer maker's own investigation showed some models might be affected.

Nvidia's director of PR and events, Derek Perez, told MacWorld the company "has worked diligently with Apple."

According to Perez:

"Our analysis shows that a failure in an Apple MacBook Pro notebook is remote. However, Apple, like other OEMs, decides on their own how to handle their warranty and repair programs, based upon their own quality standards. Regardless, we stand by our products, thus the reason why we set aside such a large reserve, and we have and will continue to work closely with Apple and their customers."