* Nikkei up 1.59%, could post small weekly gains

* Sony jumps 10% on share buyback, Microsoft partnership

* Communication equipment makers gain on rally in U.S. peers

* Investors look to Monday’s GDP, sales tax debate

By Hideyuki Sano

TOKYO, May 17 (Reuters) – Japan’s Nikkei share average jumped on Friday and looked set to end the week with a slight gain, led by rallies in Sony and technology shares, though concerns about U.S.-China tensions kept many investors cautious.

The Nikkei rose 1.56% to 21,391 points by midday. For the week, it was on track to add 0.2 percent.

The broader Topix rose 1.59% to 1,561.94, up 0.8% so far this week.

The rally was led by electric machinery and precision machinery makers, which