What was found
AVAIL AND GROUND SERVICE LIGHTS FLICKERING AFTER TERMINATING. SMELL OF BURNING PLASTIC IN FLIGHT DECK . AFTER POWERING AIRCRAFT BACK UP SMELL WENT AWAY. APU POWERS AIRCRAFT WITH NO ISSUES. REMOVED FROM SERVICE. PERFORMED OPS CHECK OF THE EXTERNAL AC POWER SYSTEM IAW AMM 24-42-00-USED DIFFERENT GPU NO POWER SURGES DEFECTS OF SMELLS NOTED A/C OK FOR SERVICE PERFORMED GVI ON RECEPTACLE PINS NO BURNS MARKS OR DAMAGE FOUND. AIRCRAFT RETURNED TO SERVICE.