You removed the monitor board with the game turned on? I don't know where to begin telling you what is wrong with that. The monitor in a Ms. Pac is rotated 90 degrees from the normal position. So, vertical foldover presents as a portion of the image on the right or left side folded over itself. What you are describing sounds more like the horizontal is not synced up right. If it won't adjust via the horizontal hold pot, make sure that the 3 pin sync connector from the video wiring is plugged in correctly. Also, it might help if you post a pic of the monitor image for us.