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CAPCOM B-21 replacement

Snax Tan

Snax Tan

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Hello there.
new in this awesome forum. i was lurking for years until now, wish to collaborate in a future.
Today i have a question.

I got a faulty knights of the round PCB.
-CPS1 A board is dead.
-CPS1-B board looks fine.
-CPS1-C board has a notorious blow at the center of the B-21 IC. this board is identical compared with my SF2CE C board.

decided to use my SF2CE A and C boards to test B board of KOTR, game works fine.
then, i use both PALs from the KOTR C board and noticed that IC1 is dead. component was dropped to the trash.
Note that B21 had a black epoxy in one of his edges, and a wire + resistor to Vcc.
after removed the dead B-21 IC i noticed this mod:

IMG_20220523_195837354.jpg

so sorry for the angle for the picure, but pads for pins 45 and 46 were ripped-off, and pins were tied to Vcc
there is a kind of de-suicide method i thought
my big question is: can i use b-21 from CPS2 A boards? i have a bunch of non- working units.
no idea if it needs extra information to "recognize" the game, but worked well with a SF2CE C board.
Thanks in advance!
 
Last edited:
Forgot to mention:
graphic Roms are arranged in different order.
5
1
7
3
6
2
8
4
 
Those two pins control the security mode that that b21 is in. They are the secmode0 and secmode1 pins. If you want to use it with the same game you had it on, tie the pins to Vcc again. The original pads were grounding it so a battery backed key could be held. Vss is putting it in a default/keyless mode.

Here is more info in case you want to learn about writing security keys https://gitlab.com/loic.petit/cps2-reverse/-/blob/master/DLs/DL-0921/doc/security-scheme.md and the pinout of the chip https://www.arcade-projects.com/threads/dl-0921-cps-b-21-reverse-engineering.15772/
 
hell yes! everything is working well!
i have tons of dead cps2 and used a b-21 from there.
recently noticed that C board to be modified is 90631C-5, while 92631C-6 is just a swap without extra wires.
Thanx a lot for your help.
 
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