Tokyo stocks were mixed Wednesday morning as selling of electronics issues tracking losses in their U.S. counterparts was offset by dip-buying after the Nikkei dropped below the 40,000 mark. The 225-issue Nikkei Stock Average fell 99.97 points, or 0.25 percent, from Tuesday to 39,997.66. The broader Topix index was up 3.98 points, or 0.15 percent, at 2,723.91. The U.S. dollar changed little around the 150 yen line in Tokyo as a wait-and-see mood prevailed ahead of U.S. Federal Reserve Chair Jerome Powell’s congressional testimony later in the day, dealers said. At noon, the dollar fetched 149….