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Thread: Sega Model 1 Info.

  1. #1
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    Sega Model 1 Info.

    I have been spending more and more time working on my Sega Model 1 boards of late. Finding it really hard to acquire much tech info on the system, I have decided to use this thread to share what i have learnt from this system with others.

    Sega Model 1 Tech.


    Model 1 LED Codes


    When the main board is operational LED 1,2,3 and 4 should all be flickering dimly. I have never seen LED 5 flicker apart from briefly on power-on. These LED’s indicate functional logic through all systems. They are designed to operate in sequence, so if there is a fault at the LED 2 range, then LED 3 and 4 will not light up.

    Red LED’s indicate a problem with the video board. If there is a fault with the Video PCB, it can be replaced with any other Model 1 Video PCB. CPU board however are locked to certain types of games. The only CPU board that is interchangeable is Wings Wars to Star Wars Arcade and vice versa. Each CPU contains a TGP (Triangle Geometry Processor) ROM which is locked to a certain game.

    If LED’s 1, 2, 3, 4, 6, 7, 8, 9 are all on simultaneously (i.e. Green and red pairs except the last two) it indicates some sort of power fault. I have heard remedies ranging from checking loose connectors to increasing the 5v lines from the cab. A full Model 1 setup will require at least 120watts total power.

    The Sound Board also has a unique set of LED codes to observe. A functional sound board will cycles through its four LED’s in order IF you have the sound running. If the game is in attract mode then the sound board will only have the power LED on.

    Model 1 Dip Switches.

    Just like CPS2, there are a number of jumper switches on the various ROM boards. These switches are used to dictate ROM size in each of the ROM banks. When replacing the 1Mbit program ROMs with 4Mbit the jumper at location “J1” will need to be changed.

    From factory all of the dip’s should be set to “off”. I am unsure of what they are used for but it stands to reason that they interact with various program code revisions.

    I/O Board

    Any model 1 PCB will not boot unless there is an I/O board present. If you do not have one then it is more than likely that you will be greeted with a solid blue screen and no logic LED’s.

    There are a couple of revisions of the model 1 I/O board but I have found that all are sufficient for testing purposes. It is also important to note that Sega used the Model 1 I/O board for the first Model 2 games including Virtua Cop and Daytona. The later I/O board revisions will not have a TOS link connector.

    Test and Service switches are located on the I/O board so it is not necessary to have these wired through your harness. There are four switches on the I/O board. These can be mapped differently depending on what firmware revision is currently written to the boards 1Mbit EPROM.

    For your Model 1 PCB to successfully boot, you will need to be supply power to CN3 and logic to CN4. Controls are wired mainly through the CN1 and CN2 connectors. Controls can either be digital or analogue and are then connected to the large filter board by use of JST NH series connectors.

    So far, I have not been able to ascertain what the different firmware versions do. Any I/O board, no matter what the firmware will work with any Model 1 game. I went out in search of game specific ones but came up empty handed. I believe though that game specific revisions might be needed for certain functions. I have also been going through the MAME source code and I believe the lack of firmware dumps is partly responsible for the poor controls in games such as Wing War and Star Wars Arcade.

    Link Board


    The model 1 link board function is similar to any other modern Sega linking hardware. Its uses a TOS-Link connector to send network packets to each linked machine via regular fibre optic cable. The Link board is located at the very bottom of the main PCB stack and also uses an EPROM to store its firmware. Model 1 games will boot with the board attached whether they use it or not, additionally, the board will remain powered at all times. The only game that I am sure uses this is Wing War for its head to head play feature. It is also possible that NetMerc uses it but it is unlikely that anyone will ever see that game in the flesh to confirm this.

    There are a number of other connectors on the Link PCB in the form of JST NH series connectors. So far I have not seem them referred to in any Sega manual

    Encryption?


    None of the Model 1 ROMS use any sort of encryption, however ROM swaps are possible if you have the right tools and lots of spare time. Each CPU board is unique to each Model 1 game with the exception of Wing War and Star Wars Arcade which are interchangeable.

    SWA and WW also both feature the same GAL chip on the ROM PCB (GAL16V8B) but VF uses a different chip and would need to be replaced in order to use the VF ROM board for anything else.

    There are two surface mount TGP ROMS that contain data used for copy protection. The Triangle Geometry Processor data is stored in the vide CPU’s onboard flash ROM and I have also been told that this data is unreadable even if you have the right tools.

    Common Problems

    By far the most common problem with any Model 1 PCB is missing 3D graphics. Fortunately, it is usually only related to bad solder rather than bad processors. Because the componentry of the Model 1 is so very tiny, it is susceptible to loosing contact with the board traces after numerous on/off cycles. (More to come on this)

    Is Model 1 Jamma?

    Yes and no. Virtua Fighter is the only model 1 game to which I have successfully converted to Jamma. The others can be partially converted to Jamma, i.e. Sound, Power, Video, Test, Service etc but because of the custom analogue controls they will never be fully Jamma compliant.

    To make a Model 1 Jamma adapter you will need a Variety of JST NH terminals (18 pin 24 pin, 6 pin etc.) A Model 1 Filter board and a Jamma finger board.

    You will also need to make a miniture amplifier as the model 1 sound boards only output line level. I made a simple box which has three RCA inputs, trim pots for each and a 2W dual mono amp. I have also decided to put a headphone jack in for testing purposes. A standard Jamma PSU will suffice for this conversion as the Model 1 only uses 5v (Logic) and 12v (Sound).

    Once I get a bit more motivation I will post some pics and wiring diagrams of my handywork.
    Last edited by Berty; 3rd January 2007 at 12:38 PM. Reason: Automerged Doublepost

  2. #2
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    I was wondering when you were going to post this...

    Very nice work m8.

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    Hi guys
    Thats some good info, thanks for the post. I'm working on a Virtua racer at the moment and all i am getting is a blue screen with no green LED's. I tried a different board in its place and that works fine so the IO board is connected and working ok. so my next though was the opto-isolator (Sharp PC910) on the CPU board coming from the IO board, but these seem to be ok. dose anyone know where i would be looking next? any info would be good.
    Thanks again
    Tye

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    I suggest swaping the various layers in the stack to isolate the effected layer. Pain in the ass but really the only way to start refining your search.

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    yea changed the layers and know its the CPU board thats the problem. the symptoms point to lose of communication to the IO board but that is good, so maybe loss of communications in on the CPU after the inputs?

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    Virtua Racing is also a network game.
    •Converting Game Gears and Atari LYNX with McWill screens and Gameboy Pocket with backlight and Bivert mods
    •Sega Saturn, Dreamcast and Mega CD region free BIOS install and power supply repairs, NEO•GEO UniBIOS install, 3DO RGB and 240p mods, DIY kits available for all.
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    Yes, it's also a racing game

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    It's alright boys, I got it fixed

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    What was the fault?

  10. #10
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    Quote Originally Posted by tye3333 View Post
    Yes, it's also a racing game
    I am not sure of the relevance there, its a Model 1 game and uses network for multiplayer, which based on original post was left out for whatever reason and was quite relevant i felt.

    I was not making any comment in relation to your issues.
    •Converting Game Gears and Atari LYNX with McWill screens and Gameboy Pocket with backlight and Bivert mods
    •Sega Saturn, Dreamcast and Mega CD region free BIOS install and power supply repairs, NEO•GEO UniBIOS install, 3DO RGB and 240p mods, DIY kits available for all.
    • CPS2 and NEO•GEO game repairs and conversions

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