Hacking Game EPROM

OldFoo · Post by **OldFoo** » Thu Nov 26, 2009 5:55 am

I was searching the forums for the dual bios mod and came across a thread where a guy talked about just changing a couple bytes in the eprom on the game cart to make it multi-regional. At the time people thought it would be easier to find a way to make a universal bios for the system itself instead of messing with the software, but in my situation i think changing a couple eproms in a couple japanese only games such as All Japan Pro Wrestling would be a better idea instead of buying a new mobo just for japanese only games. Imo it is much easier to just switch carts instead of switching the mobo and cart at the same time. Now my question is how do i find this byte and how can i go about changing it. I have an eprom programmer capable of handling anything upto 42 pins. And since i only have 1 game that requires the japanese bios imo its a no brainer to hack the rom instead of installing a dual bios mod, unless i can figure out how to do the dual bios mod. I've seen diagrams and pic on how its done but i'm not confident enough on the info provided to attempt it, however i may do so in the future if i can't figure this out.

Let me know if i'm way out there or are on the right track. Any info is greatly appreciated.

OldFoo · Post by **OldFoo** » Thu Nov 26, 2009 7:07 pm

Changing the region is the easy part, fixing the crc checksum is the tricky part. I think Alex did it but he never released it publically, and his closed his blog yet again because of the haters.

OldFoo · Post by **OldFoo** » Fri Nov 27, 2009 12:16 am

Oh damn that sucks, i'm guessing the game needs the correct checksum to work. What if my programmer automatically changes the checksum? I'm assuming the checksum is just all the bytes added together, however it might not be what the naomi is looking for so i don't know if that will work. Any more info on this is greatly appreciated!

Also couldn't you do some adjustments in the blank area of the bios to make up for the checksum difference? Basically by just subtracting the changed bytes and adding the required byte difference to a blank area, thus coming up with the same checksum that the naomi is looking for? I guess i'm not quite understanding what the problem is, or misunderstanding the problem in the first place. Or maybe i just solved the riddle, lol kinda doubt it tho

OldFoo · Post by **OldFoo** » Sat Nov 28, 2009 12:41 pm

Ace` wrote:Changing the region is the easy part, fixing the crc checksum is the tricky part. I think Alex did it but he never released it publically, and his closed his blog yet again because of the haters.

You can change the region in the game cart eprom easily, there is no CRC check there.

However the Naomi Bios is crc checked, the crc is the last few bytes of the rom image. I am not sure if people figured out the CRC format.

OldFoo · Post by **OldFoo** » Sat Nov 28, 2009 8:18 pm

Do you have an idea or know where i could find the info on changing the region of the cart though its eprom? I have an eprom programmer and have used it quite abit in the past so it shouldn't be too hard if i can figure out what bytes to change and what to change them to. Thanks

OldFoo · Post by **OldFoo** » Sun Nov 29, 2009 2:32 am

It may be easier to erase the BIOS you currently have and program it with the region you are looking for. The forum's main site has many of the useful ROM images you can use. Take a look here-->BIOS List.

OldFoo · Post by **OldFoo** » Sun Nov 29, 2009 3:35 am

I was talking about the games rom, not the motherboards. The reason is i only have one game that needs the japanese bios in order to run so i figured it would be easier to hack the games rom vs changing out the system bios everytime i want to play it.

OldFoo · Post by **OldFoo** » Mon Nov 30, 2009 2:51 am

I too would like to know how to region hack a rom. I have one I am trying to put onto a cart for myself, but it will not work due to the region on them =( Could someone point me in the correct direction? Thanks in advance!

OldFoo · Post by **OldFoo** » Mon Nov 30, 2009 3:55 am

@Xmods: Sorry, I thought your were talking about the system bios.

I've also been looking into changing the region code on games and I just needed to know how to properly calculate the checksum. I believe the checksum is based on the CRC32 method. The checksum is stored in the last few HEX bytes in the ROM programming. This is my theory in changing this:

1) Using a HEX editor, zero out the checksum (Don't forget to write down the original, just in case)

2) Change the appropriate bytes for the selected region

3) Calculate the new checksum

4) Store the new checksum at the same location as the 'zeroed' checksum

I have not yet done this myself since I've mostly researched how to do this, but this is the best theory I can come up with. :smt024

OldFoo · Post by **OldFoo** » Mon Nov 30, 2009 4:14 am

Well from what someone else said in an earlier post the checksum on the game eprom doesn't matter, but even if it did that wouldn't be hard to change. What i need to know is what address the bytes that are used to detect region coding are located and what to change them to (what options will do what, usa, jap, export, etc) this way i can find the area on my programmer once the chip is read and save it to file, then make the nessissary changes and experiment to see if it'll work on a bios from another region that the cart was not intended to play on. Basically the game in question is New(or ALL) Japan Pro Wrestling that only plays on the japanese bios equipped mobo. If the bytes are in the same location for all rom carts this would be easy, or if you know where to look in each rom for its location that info would be greatly appreciated.