The company in the middle of last week began investigating problems reported by some users that could not be resolved over the phone, Sony representative Benjamin Guernsey said.
"If we weren't able to solve the problem over the phone, we've requested they return the unit for testing," Guernsey said. He estimated approximately 100 units have been returned for testing.
The testing in most cases has been related to a widely reported problem in which the console lost its DVD video playback function after users played the Ridge Racer V game and saved game information to the unit's memory card. The software for DVD video playback can be restored. Sony has been widely reported to be recalling the PlayStation 2 because of the problem.
Testers at SCEI have not been able to determine the source of the problem, Guernsey said. The problems may have been linked to the Ridge Racer V game because the game is so popular, he said.
"That has been the most common complaint, because that's the most common software," Guernsey said. It is possible other games could also cause the problem, he acknowledged.
The highly anticipated PlayStation 2 was introduced on March 4 and currently is being sold only in Japan.