What was found
(CAN) AFTER TAKEOFF THE FLIGHT CREW REPORTED THAT THEY HAD A STRONG ELEC BURNING SMELL IN THE FORE & AFT CABIN. THEY BELIEVE IT IS ASSOCIATED WITH THE IFE SYS. AFTER TROUBLESHOOTING THE ISSUE WITH MOC & NO RESOLUTION THE CREW ELECTED AN AIR TURN BACK & ADVISED THEY WILL BE DECLARING A PAN PAN. RESOLUTION ICMT REPLACED ON SPEC REPLACED USB COUPLER & HEADSET JSCK ON FLIGHT ATTENDANTS PANEL. NO EVIDENCE OF BURNING ON ANY CONNECTORS OR WIRING. IFE PNL WIRING INSPECTED & IFE SYS OPERATED FOR 4 HRS WITH NO SMELL OR ANY FAULT, UNABLE TO DUPLICATE FAULT.