The Display to the left of the Puck Tube is a collection of PIP screens like what you would see on a Jumbo Tron screen at a football game. If Only a small portion of the screen is effected it could be the individual matrix control board on the backside of the game for the one screen. If all screens are effected double check to make sure the cooling fans are working for the Matric control boards and if they are and all PIP screens are effected the lowest matric board is the master and it most likely is the issue. To test you can swap the top board out with the Master board at the bottom, just change the dip switches to correlate with the new position.