Flip screen PCB hacks
All monitors (and TV) are really horizontal monitors. When arcade manufacturers built vertical games, they simply used a standard (horizontal) monitor and physically rotated it 90 degrees when mounted into the cabinet.
The problem is that there is really no standard that the manufacturers followed in terms of whether they rotated the monitor 90 degrees clockwise or counter-clockwise. Additionally on the older classic games, the manufacturer assumed that only their PCB would be in the cabinet, so as long as the game PCB matched the same rotation of the monitor things were fine. That means now there are a mixture of game PCBs that assume one rotation and other game PCBs that assume the opposite rotation. This makes it very difficult to swap monitors and/or game pcbs from one cabinet to another. It also creates a problem for multigame setups, whereby more than one game is being played in the same cabinet.
If you have a game that plays upside down in your cabinet, there are several possible solutions to fix it (flip it).
The simplest (conceptually) is to just physically rotate your monitor 180 degrees in the cabinet. This may be acceptable if you know that the cabinet is only every going to host the same game.
Another solution is to swap the yoke wires on the monitor. There are typically four wires that connect to the yoke from the monitor chassis. Typically they are colored Red, Blue, Green and Yellow. To flip the screen, these need to be reversed. Usually they each have some sort of slide on spade connector at the end of the near the yoke (tube). WARNING: Do not attempt this solution unless you know exactly what you are doing, there are high voltages around the monitor and also if the wires are swapped incorrectly it may result in damage to your monitor. You have been warned! I assume no responsibility. With that said, on the three monitors so far that I have done flip hacks to, all of them required Red and Blue to be swapped (reversed), and then Green and Yellow to be swapped (reversed). You can also make it switchable by adding a 4PDT switch or 4PDT relay. On some monitor chassis at the place where the 4 yoke wires connect to the main chassis PCB, sometimes there are two possible connectors, one for normal, one for flipped.
See Bob Roberts Yoke Flipping web page for more information.
Another solution is to make the game PCB flip the screen itself. It may sound complicated at first, but because most games PCBs can operate in cocktail mode, the game PCB itself already has the ability to flip the screen. On some of the newer games, the boardset may have a switch already to flip the screen, consult the game manual.
FLIP screen game PCB hacks
The left side of this document contains links to PCB hacks that can be applied to your game boards to make them flip the screen. Some are hardwired forcing the game to be in a particular rotation all the time, while some of the hacks offer switch selectable modifications.
If you have (or know of) other flip hacks for games not listed please email me with the details. Thanks!