CPS2 InfiniKey decryption key injection

Capcom CPS2 game boards contain a “suicide” battery which powers a circuit which contains a decryption table required for the game to run. If the battery runs out of charge, the decryption table is lost, and the game cannot be played.

Previously, to keep games as original as possible every 3 years or so the battery needs to be changed. If a battery died, replacement decrypted roms could be used to replace the game code, but in the interests of preservation and keeping games original many collectors avoid that option. Worst case scenario, if left unchecked a dead battery can leak acid over the game PCB and destroy it.

A new option that eliminates the need to keep and change batteries, and also resurrect games that have lost their encryption table has been released called InfiniKey. Essentially it is a small PCB which injects the decryption table into the game at power up. See this forum https://www.arcade-projects.com/forums/index.php?thread/7021-infinikey-cps2/ for details of the project and where to buy. If you buy in bulk it is very cost effective, and is little more than the cost of a battery replacement.

A YouTube video of the installation process is here https://www.youtube.com/watch?v=fZhu1_3AYHk 
I will share my experiences below, however please review the video before doing your own install.

There are 3 different types of installations across the revisions of CPS2 PCBs. Amongst my CPS2 boards I needed to do 2 of them.

First up Marvel Super Heroes Vs Street Fighter.

After popping the board open, this model has the CN9 connector and is not a rev 5, so it is the easiest of installations.

First thing to do is remove the battery. Simply flip the board over and heat up the solder joint and pull each side of the battery out from underneath for each side.

The actual InfiniKey PCB is attached to the underside CN9 connector using the row of 6 solder pads.

After tinning the solder joints on the CPS2 PCB, holder the key in place and create a join between each pin and solder pad. For this type of PCB the 93646B-5 jumper needs to be closed as this board is not that revision. Also using the game select jumpers, referring to InfiniKeyCPS2_GameSelect.pdf to close the required jumpers.

And thats it! Very simple. A very easy and neat install. Feels very sturdy provided you have solder the connection to the pads well.

Now Super Street Fighter II requires slightly more effort.

Opening the board, there is no CN9, and it is a rev 4 PCB. After removing the battery, time to do the install.

This installation uses the 4 solder pads on the short side of the PCB. It is attached to the top side of the PCB rather than underneath on the far right of the top row of pins on the CN2 connector. Once in place using same soldering method as previously, ground and +5v connections must be made. These are marked on the InfiniKey PCB, and as per the installation instructions I have tapped ground from the lower right CN2 pin, and +5v from the left side of the D2 pad. As before the game select jumpers must be bridged according to InfiniKeyCPS2_GameSelect.pdf

Again another successful installation.

I have installed these in Street Fighter Zero, Super Street Fighter II Turbo & Darkstalkers PCBs without issue.


The InfiniKeys are a great item for CPS2 collectors and I am sure they will sell very quickly due to the popularity of keeping boards with original roms, resurrecting suicded PCBs and safeguarding PCBs from potential battery damage.

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