I came across an Easter Egg in the Demo Cart. When you get to the end of the demo, hit buttons 1,3 and 4 at the same time. When you release them, the programmer's name is printed.
Fredric has communicated with the author of Video Whiz Ball and Alien Invasion, who stated that there are Easter eggs in those carts, too. I found both eggs: in Video Whizball, play a game against the computer and win or lose (it's quicker if you chose a 1-point game). Then kill the computer's man and get killed yourself. When both players are off the screen, pull up to start a new game. Choose game 43, score 67 and you'll see the egg. In Alien Invasion, start game #5 and let a blue guy die without firing any shots. With the green guy, shoot just the lowest enemy in each column. Then let all the remaining green and blue guys die without firing any more shots. Now start another game 5 and the author's name will appear at the top of the screen. Let the blue guy die without firing any shots. Play the green guy, and check out the mystery UFO that randomly flies over.
This was news to me. Looks like that old Channel F was a little more interesting than we thought.