Repairs will start next week on the Martin Olav Sabo bridge, six months after cables broke loose on the bicycle and pedestrian span over Hiawatha Avenue.The city announced today that engineers will install a retrofitted diaphragm plate, which connects cables to the mast. Workers will monitor that repair over the next month to gauge its performance, officials said, and then schedule repairs to rest of the plates. The fixes come in response to the discovery this winter that cracked plates led the longest and tallest set of cables on the bridge to break away and compromised a second set of cables below. Consulting firm Wiss, Janney, Elstner Associates concluded after a months-long investigation in June that wind-induced cable vibrations had caused the fractures. The city said the span will close to bike and pedestrian traffic starting 7 a.m. Sunday for about one week. Both directions of traffic on Hiawatha Avenue between East 26th Street and East 28th Street will also be blocked to traffic for this weekend.