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Removing the RSA check from 3DO FZ-1 console

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Shootout At Old Tucson was an arcade game made by American Laser Games in 1994. The arcade cabinet was based on a 3DO console. Sadly American Laser Games pulled out from arcade business soon after the release and therefore very few units exist. The known units are in hands of collectors rather than people who care about preservation and therefore less is known and no game play footage exists. This bugs me as the game was planned to be released to home systems. It feels to me that I should have played this game but never could as of the game's bad luck. I decided to change this situation.

3DO games are RSA encrypted. The BIOS checks whether a game is encrypted and just plays it if it is. Sadly the known arcade games are not encrypted and therefore won't play on stock 3DO consoles. I opened my 3DO in order to remove the RSA check from the BIOS. When I opened it, I saw something I wasn't prepared of: My Japanese system just has one SOP-44 ROM chip. It is common knowledge that Japanese units have two SOP-32 chips: one with the BIOS and one with the Kanji fonts. Other regions just have one SOP-32 ROM chip and the other space is left free. I thought my chip might be bigger because it could also include the Kanji information and probably has the second slot left free for arcade applications. Reading the BIOS was no easy task, as the markings on the chip did not reveal me its identity. That meant I had brute force it. First I explored some pin identities for reference purpose and to shrink the list of candidates. Then I googled all available chips for their properties and condensed a list of possible candidates. I then read the chip assuming one of these identities at a time, until I got a list of compatible replacements. After succeeding reading the ROM my suspicion was confirmed: My chip contains both, BIOS and Kanji fonts. I then hacked the BIOS to remove the RSA check. Afterwards I wrote the BIOS to an AMD AM29LV160BB, soldered it back in and set the reset pin high with a jumper wire.

All games I own still run fine. But now I am also able to run the attract mode of Shootout At Old Tucson. It still needs lots of work as I have to figure out how to interact with the game, as I lack the hardware interfaces that are present in the real arcade cabinet. Nevertheless I decided to publish this information prematurely as it brings several new and exciting things to the table and I don't know how many months it will take me to figure the rest out. Furthermore I think with too much stuff happening the episode would have become too big. Long time supporter of the show Dbn Poldermans compiled a list of games which I will try to run very soon for sure too.

But as for now: - I discovered that a hardware variant exists, which does mix BIOS and Kanji fonts onto one chip. This will become interesting for people who own a SOP-44 PAL or North American machine. - I found out that ROM chips of the 29LV160 variant can be used as 3DO SOP-44 ROM chips. Personally tested I have AM29LV160DB and AM29LV160BB. I was able to correctly read the original ROM chip by assuming the identity of clone chips too. Therefore I assume a direct compatibility of all clones and moreover all variants of these. [don't read this text, but write it into the picture] (AM29LV160**, MBM29LV**, MX29LV160**, ES29LV160**, HY29LV160**) - The RSA check can be removed from the BIOS [Put this into text only] The RSA check can be removed from the BIOS by changing the two occurrences of 000313A0000111A0 into 000313A0000011A0. It is important to leave the 000213A0000111A0 as it is. My acknowledgement goes to Taijigamer of AtariAge. He is one of the most knowledgeable 3DO enthusiasts in existence. He discussed the details shown here with me, told me about the other SOP-44 3DO systems and it was his idea to tie the reset pin high. After the usual ending screen I will attach the whole attract mode of Shootout At Old Tucson, recorded from actual hardware.