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PostPosted: Sat Feb 24, 2018 8:06 am 
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A while back I gott a nonfunctioning Sonic 3, board only.
Although it was reasonably clean, i didn't boot.
While doing random tests, I tried it with a Mega Key, just like this one:
Attachment:
File comment: MegaKey
MegaKey.jpg
MegaKey.jpg [ 107.22 KiB | Viewed 105 times ]

It showed a message telling it was designed to be played on NTSC systems.
So, I played a little with the switches and it booted fine with all of them off.
Interestingly it didn't boot alone even with a game genie.
I quickly opened it to see what's inside and I only could find an epoxy blob, the 4 switchs and some parts marked as RPx, wich I suppose are some resistors associated on a bar.

I also removed the FRAM and the logic circuits around it, routed the ROM /CE to the 74HC139 pin 1 and got the same results.
Is there anything I can try to do to make it boot alone?
It's also missing all the capacitors, except the electrolytic one.
What capacitors are these? I think they're decoupling capacitors, but I didn't find an clear enough image to see its values, would they be 100nF (104) ones?
Also, it's not saving, I fount that specific FRAM chip (FM1208S) to be expensive, maybe I could use an SRAM on its place.

Just in case someone is interested, here is some board p0rn:
Attachment:
File comment: Solda
Sonic 3 - Componentes - S.png
Sonic 3 - Componentes - S.png [ 1.16 MiB | Viewed 105 times ]

Attachment:
Sonic 3 - Solda - S.png
Sonic 3 - Solda - S.png [ 1.3 MiB | Viewed 105 times ]

Better resolution here and here.
Oh, and I noticed I forgot to take a picture of the assembled board. :-(
But I found a similar one here
If someone could please RE this board for me, I would be very happy. :-)

Thanks in advance!


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PostPosted: Sat Feb 24, 2018 9:49 am 
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I traced it out about a year ago. It's not that complex. Most of the functionality of the logic revolves around changing between sonic 3 mode as an individual cart, and sonic & knuckles + sonic 3. That gets controlled by B27 #RESET. the S&K grounds that pin permanently for the S3 cart. Could be some errors with my schematic. I only beeped out the interesting parts with a DMM.


Attachments:
File comment: Sonic 3 schematic beeped out.
2018-02-24 10.43.53.jpg
2018-02-24 10.43.53.jpg [ 2.4 MiB | Viewed 90 times ]

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If you're gonna play the Game Boy, you gotta learn to play it right. -Kenny Rogers
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PostPosted: Sat Feb 24, 2018 11:01 am 
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This reminds me of my own problems with my Sonic 3 cartridge I've had since 1994. It never saved games, but I didn't consider this a major issue as a kid. Only recently I got curious about it again and decided to check what could be the problem, and to my surprise, the FRAM appeared to have been intentionally disabled, as one of the traces leading to it was cut.

I have no idea why anyone would do that, specially considering this was an original TecToy cartridge, bought sealed from a respectable store.

I haven't tried to restore that trace yet, but I guess it would be cool if my cartridge was finally able to save.


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PostPosted: Sat Feb 24, 2018 11:06 am 
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infiniteneslives wrote:
I traced it out about a year ago.

Thanks!
That's cool!!

An interesting thing I noticed is that my game (besides the 74HC139 and the 74HC74) uses 2x 74HC00, while yours use an 74HC157 and a 74HC00.

I finished my 1st RE try a whyle ago.
I also lokked at the FeRAM circuit only.
Probably has lots of mistakes/omissions:
Attachment:
File comment: Try 1
Sonic3 RE - Try1.png
Sonic3 RE - Try1.png [ 1.16 MiB | Viewed 74 times ]

I don't think a SRAM mod would be much difficult, but I have no idea where I could put a socket for a battery and be able to close the cartridge normally. :roll:

I also found something about the MegaKey here.
Altough it's a MegaKey 2, I don't understand properly the schematics and didn't found the IC's datasheet around. :oops:
Looks like there's lots of NANDs and 2 latches on the final draw.

Maybe I have a problem with the MaskROM.
That could explain why the thing only boots with the adapter.
And I tought they were almost undestructible!! :-b

tokumaru wrote:
I have no idea why anyone would do that

That's odd!!
I think this one is a TecToy too.
The difference is that I got this as garbage.
I also have high hopes to get it working properly!!


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PostPosted: Sat Feb 24, 2018 1:20 pm 
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Fisher wrote:
I also found something about the MegaKey here.
Altough it's a MegaKey 2, I don't understand properly the schematics and didn't found the IC's datasheet around. :oops:
Looks like there's lots of NANDs and 2 latches on the final draw.
That schematic looks like a lot of "generate a bus conflict and win!1!one"

that page wrote:
It consists of two input elements DD1.1 ("AND-NOT", address 508000H) and DD1.2 ("And", address 600002H).
Hm, adjust the addresses, and that's getting in a fight with $A10000, the VERSION NO register, where D7 is Intl/!Jpn and D6 is PAL/!NTSC
and $C00004, the VDP STATUS register, where D0 is VDP PAL/!NTSC



The schematic of your Sonic 3 cart looks like a fairly standard 4MiB game + battery-backed RAM SMD cart schematic to me...


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PostPosted: Sat Feb 24, 2018 3:21 pm 
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That's pretty interesting!
But I don't understand why the game boots with the adapter and not without it.
Any ideas?

Maybe the resistor bars have something to do with this...
I'll take a look at what they're doing.
I think a picture should be helpful too...


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PostPosted: Sat Feb 24, 2018 4:15 pm 
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Hm, I was actually only describing what was in Рис.1 and Рис.3

I hadn't actually looked at Рис.2 ... but looking closely now it appears to be describing the reverse-engineering process.

Рис.4 and Рис.5 are an all-new-parts implementation of the same schematic, using Soviet part numbers.

Quickly looking things up:
КР1533ЛЕ4 ↔ 74'10
КР1533ЛА1 ↔ 74'20
к555ап5 ↔ 74'244
КР1533ЛА2 ↔ 74'30


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PostPosted: Sat Feb 24, 2018 8:12 pm 
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Joined: Sun Jun 12, 2011 12:06 pm
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Location: Poland
Image

More info about cartridge pins signals description:
http://www.hardwarebook.info/Mega_Drive_Cartridge


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