CPS II decrypt help please

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joemagiera
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CPS II decrypt help please

Post by joemagiera »

Hi all,

I have a CAPCOM CPS II Super Street Fighter II Turbo (USA version) with a dead suicide battery.

I downloaded the decrypted ROMs for this game, ssf2tur1di.zip. Just as a sanity test before taking apart the B board, burning and replaced the ROMs, I renamed the decrypted ROMs to match the MAME ROMset ssf2tur1 and tried firing up the game in MAME. Since there wasn't any key in the decrypted ROMset, I used the key in the un-encrypted ROMs. The ROMset did not work in MAME. It just came up with a alternating blank streen then a screen with garbage. Back and forth, same thing every few seconds.

Shouldn't the decrypted ROMs work in MAME? Do I need to use a different key? I'm sure I'm doing something wrong. If anyone has any ideas/advice/works of wisdom, it would be much appreciated.

This is the first time I'm ever trying anything on a CPS board, so this is all new to me. Thanks,

Joe (joemagiera at ameritech dot net)
joemagiera@ameritech.net
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yosai
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Re: CPS II decrypt help please

Post by yosai »

You can check the board is definitely dead with Razoolas suicide tester. Link at the bottom of this page.

http://cps2shock.emu-france.info/suicide.html

If it has died and you want to run the decrypted set. Remove the battery, short capacitor CC1, burn and install the program EPROMs.
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nem
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Re: CPS II decrypt help please

Post by nem »

joemagiera wrote: October 24th, 2021, 3:17 pmSince there wasn't any key in the decrypted ROMset, I used the key in the un-encrypted ROMs. The ROMset did not work in MAME.

Well, no, because Mame is now trying to decrypt the already decrypted game files with the encryption key from the encrypted set.

Anyway, the set will be fine. Just burn it to some eproms.
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Re: CPS II decrypt help please

Post by joemagiera »

nem wrote: October 24th, 2021, 5:49 pm Well, no, because Mame is now trying to decrypt the already decrypted game files with the encryption key from the encrypted set.
I understand what you are saying and I will go ahead and do it as instructed, but wouldn't a real PCB do the same thing as MAME (use the encryption key on the now decrypted ROMs?
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Re: CPS II decrypt help please

Post by nem »

joemagiera wrote: October 25th, 2021, 1:54 amI understand what you are saying and I will go ahead and do it as instructed, but wouldn't a real PCB do the same thing as MAME (use the encryption key on the now decrypted ROMs?

No, because you don't have the decryption keys any more on the board. When the battery goes flat, the keys are lost.

Personally, I would reinject the keys, put a new battery on the board, and use the original roms. So once you have verified your board is working with the decrypted roms, you can look in to that. It can be done pretty easily with very cheap hardware. If you don't want a battery because of the risk of it leaking or exploding, you can look into an Infinikey or other hardware that will reinject the keys on every power up.

Anyway, if you want to see the decrypted rom set working in Mame, just write FF over the key with a hex editor:

ssf2t_decrypted_set_key.jpg
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Re: CPS II decrypt help please

Post by joemagiera »

yosai wrote: October 24th, 2021, 3:29 pm If it has died and you want to run the decrypted set. Remove the battery, short capacitor CC1, burn and install the program EPROMs.
Last question on this (I hope), on the "short cap CC1", I'm just soldering the two cap legs together and leaving it permanently shorted, is that correct?
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Re: CPS II decrypt help please

Post by yosai »

Just short the two points together with something metal while it's powered off. It's just to remove any residual charge that may be in the capacitor.
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Re: CPS II decrypt help please

Post by joemagiera »

I tested with the suicide tester ROM today. I removed the battery and shorted the EXC1 pins. Nothing, dead, just a solid green screen. Bummer.

The A board has never been opened.

The B board was never previously opened before I opened it.

Bummer, oh well. Would have been nice if at least the A board was working. I know it still could be, but I have no further way to test.

Thanks all for the help and advice. I never worked on these before. Learned a lot.

Joe
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