(Recasts; adds comments from conference call)
SAN FRANCISCO Aug 12 (Reuters) - Nvidia Corp (NVDA.O) announced a $1 billion boost to its stock buyback program, sending shares of the graphics chip maker up 10 percent despite announcing a quarterly loss on a one-time charge and revenue that fell short of Wall Street expectations.
Chief Executive Jen-Hsun Huang called the second quarter results "disappointing," and said the PC market slump and a "miscalculation" of the company's competitive price position were to blame.
Nvidia, which designs chips called GPUs, or graphics processing units, used for three-dimensional scenes in computer games, faces intense competition from Advanced Micro Devices Inc AMD.N and Intel Corp (INTC.O). Both rivals have been aggressively pushing into the GPU market.
Huang said it was hard to predict when the desktop computer business would stabilize.
"We didn't lose any share, the market just got soft on us," he said on a conference call.
The net loss for the second quarter was $120.9 million, or 22 cents a share, compared with a profit of $172.7 million, or 29 cents a share, a year ago.
Excluding items, the company reported earnings of 13 cents a share, short of the average analyst expectation of 17 cents a share, according to Reuters Estimates.
The latest quarter's results included a $196 million charge to cover warranty, repair, return and other costs related to versions of its products used in notebook computers.
Revenue fell to $892.7 million, a 5 percent decline from $935.3 million a year ago and below the $907.6 million expected on average by analysts.
Nvidia executives said on the conference call they expect revenue to grow "slightly" in the third quarter.
Nvidia shares rose $1.13, or 10 percent, in extended trading after the company said it was increasing its share buyback program by $1 billion to $2.7 billion. The shares had closed regular trading Tuesday on Nasdaq at $11.07. (Reporting by Anupreeta Das; Editing by Tim Dobbyn)