AST Research Inc, Irvine, California has taken a hit from Standard & Poor’s Corp, which cut the personal computer manufacturer’s subordinated debt rating to B-minus from single-B. The senior implied rating is B-plus and rated debt totals $315m. The downgrade reflects recent net losses caused by new product delays and component shortages, as well as the volatile nature of the personal computer industry, the agency said. AST has had a largely successful record of revenue growth and innovative product development. The June 1993 acquisition of Tandy Corp’s personal computer manufacturing operations significantly improved AST’s market position, but the ratings agency is still worried about AST.