What was found
(CAN) ON CLIMB OUT, CO-PILOT'S PRIMARY DISPLAYS LOST ALL VIDEO DATA, AND SCREENS HAD A RED X. THIS WAS QUICKLY FOLLOWED BY THE SAME LOSS OF DATA AND RED X ON PILOT'S PRIMARY DISPLAYS. EICAS BEGAN TO FILL UP WITH NUMEROUS AMBER MESSAGES, THEN PILOT'S ANDCO-PILOT'S DISPLAYS RETURNED TO NORMAL AND ALL EICAS MESSAGES WERE GONE. THIS ALL HAPPENED OVER A PERIOD OF ABOUT 20-30 SECONDS. PILOT'S WERE OVERWEIGHT FOR LANDING AND PERFORMED SOME TESTING FOR A PREVIOUS FLIGHT SNAG. APU WAS STARTED AS A PRECAUTION, AND A/C RETURNED TO MONTREAL. THERE WERE NO MORE PROBLEMS UNTIL AFTER ENGINES WERE SHUT DOWN, WITH APU ON LINE. CO-PILOT'S DISPLAYS LOST VIDEO DATA WITH THE RED X AND THERE WERE NUMEROUS AMBER EICAS MESSAGES.