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Thread: Mega Drive will not tell the Mega CD to start?

  1. #1
    The Cat in the Hat Shining Hero NeoVamp's Avatar
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    Default Mega Drive will not tell the Mega CD to start?

    Now I know what you're thinking, replace the capacitors! but I already did.
    I replaced the caps on the MD mobo and it works fine, and I replaced the caps on the Mega CD mobo (which boots fine with another MD that hasn't been recapped yet)
    But when I hook up both recapped systems the MD just won't tell the MCD to start, no lights nothing.

    However, if I boot with the Mega Everdrive and start any CD bios from there the MCD lights up and I can eject the tray. (I forgot to test a game)

    Any idea where I can look on the Mega Drive side?
    Last edited by NeoVamp; 02-21-2019 at 07:47 PM.

  2. #2
    Hedgehog-in-Training Hedgehog-in-TrainingNameless One pyroesp's Avatar
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    Whenever the MD is turned on, there's 9V going to a transistor on the Mega-CD, which switches the power going to the 5V linear voltage regulator.
    This 9V from the MD is hardwired if I remember correctly, so not depending on the Mega-CD bios or other logic.

    My guess would be that you have an issue with your Mega-CD bios chip, as it only works when you load a Mega-CD bios from the Mega Everdrive ?

  3. #3
    The Cat in the Hat Shining Hero NeoVamp's Avatar
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    Quote Originally Posted by pyroesp View Post
    as it only works when you load a Mega-CD bios from the Mega Everdrive ?
    No, the Mega CD works fine with a 2nd Mega Drive, its just that the first recapped MD wont boot the MCD but will work fine if I load an external bios.
    Its like the fixed MD somehow can't send the wakeup call to the MD.

    I'm gonna take the MD apart again today and see if I can find something.

  4. #4
    Nameless One vexatious's Avatar
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    check male plug on recapped md. Look for dirty or corroded pins. Rub down metal pins on male plug with pink eraser on both sides being careful not to pry any pins that may be loose, then wipe clean with lint free camera lens cleaning cloth with half-water half-alcohol mix.

  5. #5
    The Cat in the Hat Shining Hero NeoVamp's Avatar
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    Cleaned the expansion connector (actually already did that before) and did not make a difference, But I did find something else that might point to where the problem lies.

    If I put the game cartridge SUPER STREET FIGHTER II in the recapped MD (without MCD) then it will NOT boot (freezes right when the blue SEGA logo wants to fade out), however when I hook up the MCD to the MD then it WILL boot.
    Its almost like there's a data line not working, and that's the one that the game SUPER SF2 needs to reach the mapper chip to be able to access the extra 8M that the game comes with.

    It would not surprise me if this is the same expansion data line (or whatever its called) that also tells the MCD to turn on.

  6. #6
    The Cat in the Hat Shining Hero NeoVamp's Avatar
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    I have it working! (kinda)

    Somehow after going back to it Super SF2 suddenly did work, with and without the MCD attached.
    So I started going through MD schematics trying to localize where the problem would be, the PDF just said it might be the Fujitsu Sram chip which I could not locate (maybe I was looking at the MCD schematic?)

    Anyhoo, so I'm googling and I find people talking about a Mega Drive test cartridge, and one of them linked to the rom.
    So I put the rom on my Mega Everdrive SD card and did all 6 possible tests (A-123 B-123) and it found no problems.

    So I decide to swap cartridges and try out some other games before going back to the Mega Everdrive and because of the way I was sitting and the MD being open and all I accidentally did not put it in right. (it was a bit arched, with the right side of the cartridge not sticking in completely) (as viewed from the front)

    And suddenly I was greeted by the Mega CD lights on the front and music!

    And all because the cart is not seated correctly.

    Anyone? do I need to look at the cartridge pins? I cleaned them with the creditcard method some time ago so I know its clean.

  7. #7
    The Cat in the Hat Shining Hero NeoVamp's Avatar
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    Problem fixed, the cartridge slot was too tight so I made it less tight by putting some plastic cards in there until it was back to normal.
    Everything boots fine now, such an easy fix I feel kinda silly for diving into so deeply.

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