What was found
AFTER PUSH BACK IN GATE WITH BOTH ENGINES RUNNING, CARGO SMOKE LIGHT CAME ON AND OFF TWICE. PASSENGER REPORTED TO FA SEEING SOMETHING WHILE COMING OUT OF ROW 10B AIR GASPER. RETURNED TO GATE. MAINTENANCE INSPECTED CARGO SMOKE DETECTOR WIRING AND AFT FLIGHT RECORDER BAY AND OVERHEAD PSU 9CD, 10CD, AND 11CE, FOUND BALLAST OVER SEAT 10CD HAS BURNING SMELL, VERIFIED THE WINDOW LIGHTS INOP. MAINTENANCE REPLACED BALLAST. ALL CHECKS GOOD.