Customized JAMMA switcher for 2-in-1 light gun arcade

So here is the dilemma… You buy a video game cabinet and then decide that just having only one game in it does not satisfy your inherent need to make it contain more than one game. And what if you cabinet was a ‘gun’ game for which that type of arcade machine is at a distinct disadvantage for using with MAME type emulation? Well there ought to be a way to switch between multiple game PCBs right? Well yes there is, you can get a switcher for just this purpose… But, after implementing such a setup, I don’t recommend it. Read on for more details….

Here is my Lethal Enforcers II arcade machine that I purchased many years ago. Some point after I acquired it, I decided to purchase the PCB for the original Lethal Enforcers arcade machine for which I remember playing so much in the college dorm laundromat. For years I got by just having the 2nd PCB mounted to a tray inside the cabinet and swapping the JAMMA and gun connectors when I wanted to switch games. This was fine if just a little kludgy.

But it just so happens that there are products intended to solve the problem of switching all of the wires in the JAMMA harness between PCBs that sort of work. Here is the one that I purchased:

It seems like it should be a straight forward task to switch between two game PCBs, but it is not. To make wiring a video game cabinet a standard practice so that a different game board could be swapped into a cabinet without changing the wires, the JAMMA (Japan Amusement Machine and Marketing Association) connector was invented. It standardized the pin-out on game PCBs and the associated wiring to components in the arcade cabinet. There any many different types of signals in play on a JAMMA harness. Including:

1. Power: +5v, +12, -5v (not used by most PCBs) & Ground
2. Sound: Mono “+” and “-” speaker output
3. Video: Red, Green, Blue, Sync and Video Ground lines.
4. Contol Inputs: Joystick (Up, Dn, L, R), Buttons (Shoot, Start), Coin Trigger, etc. [for two players]

In addition to the standard JAMMA harness, this cabinet also has extra connectors for the two optical guns and stereo speakers. So how will this switcher handle that? Not very easily it turns out.

Let’s look at the switcher as it arrived:

The basic theory of operation for this switcher involves using relays and diodes to switch back and forth between the two games when the button on the wireless remote is pressed. The relay on the right of center alternates routing the +12v and +5v power feed between the PCBs. Note that this switcher does not switch the -5v signal between PCBs, instead it leaves those pins unconnected. This is not an issue since most PCBs do not use the -5v power feed. The second relay alternates routing the speaker connection between the PCBs. The remainder of the connections (video and control signals) are tied together from both PCBs to the cabinet JAMMA harness. The two rows of diodes prevent signals from one PCB from from entering the opposing PCB. Since only one game is powered up at a time, the arrangement works. But there is a problem, if you look closely at the spots between the pin connectors, there are spaces for eight diodes that are not installed. Unfortunately these missing diodes were intended to separate the video signals (Red, Green, Blue & Sync). As a consequence, it can be said that this JAMMA switcher fails to work as advertised. Strike one against the idea of easily switching between PCBs in the same cabinet.

On to the modifications! Hint: Lots of relays.

Six DPDT relays to be exact. By using relays, the signals for Video (Red, Green, Blue, Sync), Stereo speakers (L+, L-, R+, R-), and both of the optical guns (trigger and optical sensor) are able to be switched cleanly across both PCBs. The +12v pin going to the PCB #2 JAMMA connector is connected to the coil of all of the relays. So when game #2 is active, all six relays are switched on and the above connections are switched over to PCB #2.

Also note that the +5v and ground wires that power the optical sensors for both guns are not switched through the relays, instead they are connected directly to constant +5v and ground. This arrangement powers the guns’ optical sensors directly from the power supply and not through the switcher. Lastly of note, the video ground pin for both JAMMA PCB connectors were separated from the power supply ground and tied together. So the video ground pins of both PCBs are jointly connected to the monitor and nothing else. After soldering all of the various connections to the original switcher and creating jumper cables for the guns and speaker connections, this monstrosity is now complete. Final score: power, start buttons, service switch and coin triggers are routed through the switcher’s relays and diodes and everything else including video signals, optical gun signals and the stereo speakers are routed through the add on relay board.

Here is the finished product:

Here it is connected to PCB #2 (Original Lethal Enforcers). The two gun connectors are on the left side and the stereo speaker connector is on the right side.

Here is the switcher and relay board installed in the cabinet:

The PCB original to the cabinet (Lethal Enforcers II – The Western) is in the background. The second PCB (Lethal Enforcers I) is in the foreground. The game select button was installed in the front of the cabinet next to the coin door.

Video of the switcher in action:

Final thoughts:

While this was quite a bit of work, the final product does work pretty well in my case. Switching between the two games in my cabinet is seamless. However given the low quality of JAMMA switchers that are still available for sale, I would not recommend purchasing one unless you are prepared to solder on it.

The only small issue that I have with the final product is the monitor. Monitors in these older game cabinets have manual analog controls that need to be adjusted to produce the best picture for the game that was installed in the cabinet. Since only one game was installed at a time, the picture could be properly centered and the brightness and contrast controls set just right (very important on an optical gun game). When switching between two games, the picture settings need to be a compromise between the two. In my case, the brightness setting needed to get reliable gun hits in LE II caused the picture to be somewhat washed out in LE I. But I can live with that. If you are thinking about doing a 6-in-1 light gun cabinet like in the link below, note that it could be very difficult to get a good picture on all six games without having to adjust the monitor every time the game is switched.

GAME OVER

Further reading on JAMMA switchers & Light gun games:
https://forums.arcade-museum.com/showthread.php?t=271012