(Corrects strategist's name in fourth paragraph)
* Chip-related stocks tumbled after Sox index fall overnight
* Pioneer volatile after funding news
By Ayai Tomisawa
TOKYO, Sept 12 (Reuters) - Japan's Nikkei fell on Wednesday as chip-related stocks tracked weakness in their U.S. counterparts overnight and as machine tool makers weakened after downbeat industry data.
The Nikkei share average was down 0.4 percent at 22,571.76 points by the midday break, after rising 1.3 percent to a one-week high on Tuesday.
Worries about escalation in the Sino-U.S. trade war and the outcome of U.S.-Japan trade talks also added to the gloomy mood.
"There is so much uncertainty over global trade issues. We want to first know how Japan's key auto industry will be affected," said Kazuhito Suzuki, a strategist at Shinkin Asset Management.
A source told Reuters on Wednesday that Japanese Economy Minister Toshimitsu Motegi and U.S. Trade Representative Robert Lighthizer will likely hold a second round of trade talks on Sept. 21 in the United States.
Their meeting is planned to precede an expected summit between Prime Minister Shinzo Abe and President Donald Trump on the sidelines of a U.N. General Assembly General Debate starting Sept 25, the source said.
Chip-related stocks were under pressure after the Philadelphia SE Semiconductor Index dropped 1 percent overnight.
Semiconductor device maker Rohm Co dived 9.9 percent to hit a one-year low, while high-purity silicon maker Sumco Corp stumbled 7.8 percent and Advantest Corp dropped 3.2 percent.
Machine tool makers stumbled after the Japan Machine Tool Builders' Association said machine tool orders for overseas markets in August dropped 4.4 percent on the year.
Tsugami Corp dived 6.6 percent, Okuma plunged 5.2 percent, DMG Mori dropped 3.0 percent and Makino Milling Machine shed 2.2 percent.
Struggling consumer electronics maker Pioneer Corp was extremely volatile, soaring as much as 6.2 percent before ending the morning session down 9.3 percent.
Pioneer said it had secured up to 60 billion yen ($540 million) in funding from Hong Kong-based fund manager Baring Private Equity Asia (BPEA).
"Pioneer's life was extended through the funding for now, but it's unclear how the company's is trying to survive and which profitable core business it has," said a fund manager at a Japanese asset management firm.
The broader Topix shed 0.7 percent to 1,686.64. (Editing by Kim Coghill)