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Hacked a 21pin mod to 20 pin saturn

Discussion in 'Saturn Dev' started by Pinchy, Nov 19, 2004.

  1. Pinchy

    Pinchy New Member

    Here are some notes on how I hacked the 21 pin modchip to a 20 pin Saturn. [the one available from Jandaman]

    21 pin Saturn:

    //mod chip legend//

    *=used but not altered

    +=pad selector for 4MHz clock

    X=used and replaced data stream

    Y=signal conditioned ;<strobe>-||-/\/\/\-GND

    *1 -> IC 20 315-5746 pin 7 [8MHz clock] pad B

    *2 -> Ground

    X3 -> SH-1 Pin 107 DATA

    X4 -> SH-1 Pin 108 Stop packet strobe[response byte?]

    5 -> SH-1 Pin 101 OE

    6 -> SH-1 Pin 100 Start packet strobe[command byte?]

    *7 -> SH-1 Pin 111 WR strobe

    8 -> Ground

    +9 -> unused R48 [alternate 4MHz location diff rev.?] pad 0019

    10 -> YGR-019B pin 123

    11 -> SH-1 Pin 79

    12 -> Ground

    Y13 -> YGR-019B pin 126 and 129 OE fetch data

    +14 -> YGR-019B pin 125 and 131 [4MHz clock] pad 0014

    X15 -> YGR-019B pin 130 CD buffer DATA

    16 -> Ground

    17 -> IC 39 VHC08 pin 2

    18 -> YGR-019B pin 122

    19 -> YGR-019B pin 118 via 300 Ohm R175

    20 -> YGR-019B pin 128

    21 -> YGR-019B pin 121

    pin 15 data is switched on 157 multiplexer between original and GAL

    pin 3 data is routed through EM78 pins 12,9

    pin 4 data is routed through EM78 pins 7,8

    20 pin Saturn:

    1 -> SH-1 Pin 79 logic HIGH

    2 -> Ground

    3 -> SH-1 Pin 107 Data

    4 -> SH-1 Pin 108 Stop packet strobe[response byte?]

    5 -> SH-1 Pin 101 OE

    6 -> SH-1 Pin 111 WR strobe

    7 -> SH-1 Pin 100 Start packet strobe[command byte?]

    8 -> Ground

    9 -> JP5 [8MHz clock]

    10 -> Ground

    11 -> YGR-019B pin 124 ??? logic low

    12 -> YGR-019B pin 125 Read strobe

    13 -> YGR-019B pin 126 OE

    14 -> Ground

    15 -> YGR-019B pin 128 Data Read OE [?] active only during data fetch

    16 -> YGR-019B pin 129 OE fetch data

    17 -> YGR-019B pin 131 [4MHz clock]

    18 -> YGR-019B pin 130 CD buffer DATA

    19 -> Ground

    20 -> R47 (4.7KOhm), not sure where the other side of R47 goes ATM...

    The pins that you have to cut and reroute on the modchip are


    the hardest part is transferring 15->18

    C=plastic ribbon connector

    E=edge connector of modchip

    What traces to reroute:

    Cut pin 7 C -> pin 6 on EM78

    Connect Pin 6 EM78->pin 5 C

    Cut pin 13 C -> Cap

    Connect Cap-> pin 16 C

    Cut pin 15 E -> pin 12 157

    Cut pin 15 C -> pin 14 157

    Cut pin 18 E -> pin 18 C

    Connect pin 12 157 -> 18 E

    Connect pin 14 157 -> 18 C

    Connect pin 15 E -> pin 15 C

    Remove solder from pads 0019,0014

    Connect middle pad -> pin 17 C

    remove solder/jumper/connection from A/B pads

    Conect pad A [8MHz]-> Pin 9 C

    Trim off pad 21 with dremel and you're done ;)

    My problem now is that the ribbon cable is too short if you want to install the modchip in the Saturn motherboard. You should be able to install it into the CD drive connector, but I have wires for my logic analyzer soldered down to the pins which are in the way. My modchip has to have components facing away from the CD. Pin 1 is towards the rear of the console on my model 1 as pin 1 on my model 2 is towards the front. Is that not crazy or what?

    Right now I just have the CD drive off its posts closer to the chip so the ribbon will reach. It's ugly as hell but it works. Just take care of the ordering of the pins. The connector on the CD drive on my model 1 Saturn are numbered backwards from the numbering scheme on the MB. But my model 2 is the same. The numbering used above is for the Connector on the MB.

    I haven't had a chance to analyze what the Chip alters yet. Any pointers would be helpful. I'll have to do a lot more soldering and cutting to see before and after. ;)

    Looks like there's a command $4d to read the ring. If I put in a CD-R, it seems to check the country code first. Then, if that's ok, it moves to the outer ring and tries to read it. If it doesn't, it moves in closer and closer to the center in about 5 or so steps and then gives up. During this whole process, the first byte of the command packet, as I call it, reads $4d. Some of the CDC commands I think carry over directly to the drive like $01 is for get status.

    Kudos to mal, ExCyber and the rest of the SegaXtreme gang for their wonderful posts.

    I just want to say: MR Sporty, where are YOU?! I've tried to message and mail him, but I got no response. IIRC, he had the analyzer setup for before and after reads of the modchip. I wish I could talk more with you about what you've found and maybe do some more work to completely reverse this CD-ROM. Once it's all laid out, it should be a piece of cake to add a cypress Fx2 USB chip to emulate the CD-ROM or even add an IDE drive. I've already done it for the GameCube, but I'll admit it was much easier to reverse than this beast. ;)

  2. racketboy

    racketboy Member

    And availible from racketboy (in a couple weeks) :D

    Anyway, this is awesome news as it gives another large piece of the Saturn community the option to mod their machines

    This thread MIGHT want to be moved to the normal Saturn forum and possibly stickied.
  3. ExCyber

    ExCyber Staff Member

    Wow, this is great news! I'm glad someone was able to make use of that info. :D
  4. madmalkav

    madmalkav New Member

    Some wild guessing:

    If we made a big enough preorder to jandaman or any other store that stocks that stuff , you think they will get Xinga -or whatever that produces their chips- to made the changes in factory?
  5. racketboy

    racketboy Member

    I could possibly try to do some, but I'm not a big electronics expert.

    I have 25 chips on the way.
  6. AntiPasta

    AntiPasta New Member


    Now that would be nice, especially with the imminent decline of CD lasers. Best of luck! If you succeed I'll send you some money to get drunk :D
  7. racketboy

    racketboy Member

    so has anyone successful performed this yet?

    a more newbie-friendly tutorial would also be appreciated, if possible.
  8. mal

    mal Member

    Just some pics would be a great start.
  9. Pinchy

    Pinchy New Member

    I was reluctant to post some pics coz my camera is so crappy but here it is.

    The 4 traces you cut are all right in a row on the back and one is on the front where u solder the wire to.

    You can get that 1mm pitch flat flex cable from digikey and ZIF female connectors too.


    The part numbers are

    WM10085-ND CABLE FLAT FLEX 20POS 1MM 10"


    you can get one of the fpc connectors and solder it to a 4" flex cable and use that to extend the connector out of the saturn mainboard [On my saturn I had to trim some of the metal shielding out of the way for the modchip to plug in directly like on 21pin sat's] ,that way it just makes it easier and you can tuck the chip out of the way.

    Hope this helps

    Attached Files:

  10. Chris5687

    Chris5687 New Member

    that stuff is absolutly amazing man. You should get together a nice guide for it, so many peolle could use it, but oyu need a guide up, cause once one is up it can be used forever. That's gotta be a good feeling.
  11. Protosstic

    Protosstic New Member

    Yeah, would you be able to create a guide on how to do this? Truly appreciated!
  12. madmalkav

    madmalkav New Member

    If I can get the parts domestically and get some free time for job I will try it for sure.

    Thanks it for the awesome work.

    P.S.: Pinchy = tmbinc ?
  13. Protosstic

    Protosstic New Member

    Haven't heard any more about this lately, you still around man? Thanks!
  14. mayden

    mayden New Member

    Has any else tried this modification? I'm pretty curious, have a model 1 myself. It doesn't look easy to fix this job.
  15. mal

    mal Member

    Who ever said it was going to be easy?
  16. Drenholm

    Drenholm New Member

    I'd like to try this, but my electrical skills are next to nothing! :)
  17. mayden

    mayden New Member

    I did't, did I? Compared to the modding instruction of a model 2, this looks far from easy. The thing is, if I can verify that this instruction does work for another 2 or 3 people, I'm willing to take the chance and try it myself.
  18. seal1

    seal1 New Member

    on your PHTO0005.JPG it looks like

    Connect Pin 6 EM78->pin 6 C

    --- 6 not 5 ???

    pin 6 em78 goes to upper row, which is even -> so 6 not 5 ?, coz you cutted connection to 7 which is lower row of connector, so upper must be 6 not 5 ?

    beside my 20pin saturn is a other version, leds on upper case not "lightchannel" from pcb to upper case like yours.


    and for the records a pic of my other saturn a 21pin/round button (mb = VA9) chipped with EMSIC7-modchip with IN OUT cables switched and working since years.




    thanx again for your very fast delivery.

    Attached Files:

  19. seal1

    seal1 New Member

    I did some paintwork ... with "Connect Pin 6 EM78->pin 6 C" as I think not to "5 C"

    7 wires, 5 cuts, 2-4 desolder, 1 dremeljob:



    please check this image and give me a "go" or "no-go"

    ordering on cd-board seems on my model also backwards. mb 1 = cd 20 like yours. so if I install modchip on cd-connector components will facing away and there is metalshield which needs to be cutted.


    Attached Files:

  20. mayden

    mayden New Member

    Good job seal1, the scheme looks pretty damn good! I can see the wire en cutting jobs clearly. The smal red ones are the cuts I presume? But could you be a bit more specific on the "2-4 desolder" thing? For example those two in the top-left corner. I can't really make out which thing to desolder. I presume the modchip in this photo is in it's original state, so it's pretty hard for a n00b like me to figure out how it should be in it's "modded" state.

    edit: in the scheme, what's that small yellow dot in the bottom-left corner? A wire cut?

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