Have you checked all of your fuses? And by checking, I mean with your DMM? Also, check the fuse holders. That type of fuse holder is notorious for corrosion or just the sides becoming weak or breaking off. If everything is good there, keep moving on down the line. Check the wiring to the harness and check for broken or corroded wires at the harness connector. Pins inside the harness can get dirty or even weak so there may not be a good contact at the edge connector. Those are the basics. Now when you are saying you are getting power to J5 are you talking about the power board or the game board? I have not worked on a Centipede, but have brought several others back to like from same era.