I wired up the 5v and gnd to both the top and bottom board. Then I checked for out coming signals on the bottom board. On the screen of my scope I found only one pin with a signal. I was expecting more? Then I took a closer look at the signal and it appeared to me it could be composite video.
Did they use composite video on arcade boards? A quick search on the net taught me they did. Mostly on B&W cocktail tables so this should be it.
Now my test rig isn't capable of playing composite video

so I hooked up a small video device in MacGyver style. And there was an image

.
The ball stops moving as soon as the image is steady, but with the crappy connection the picture goes on and of having the ball move jerky.
I also discovered the big switches on top don't respond. You should be able to put the game in play or test mode, but it seems it's only in test mode (large padel). Also the flip screen does nothing? So there is definitely some work to be done on this board.
But this solves the mystery, it is a zunzun block board. Now I have to find a way to display the composite video on a crt so I can try to get this game up and running like it did in 1979.