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Thread: Neo Geo MV-1ACHX UniBIOS install issues: Is piggyback an option?

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    Neo Geo MV-1ACHX UniBIOS install issues: Is piggyback an option?

    Well, after getting my AES up and running, I moved on to an MVS board I've had sitting around. I've been taking the necessary steps to consolize it and get it ready to go. Everything has been fine until I installed the UniBIOS this afternoon. It's a Chinese variant of the MV-1A board, the MV-1ACHX, but everything I've seen about the MV-1A board has been relevant to this revision. I'm assuming it's just a regional code.

    Since (presumably) there won't be any future UniBIOS updates, I opted to piggyback the socket instead of a full removal and socket install. Everything went smoothly: clipped and lifted leg 2 of BIOS chip and socket, soldered the remaining 39 legs together in the stack, ran a 15K resistor from BIOS leg 2 to pin stack 40, and ran a wire from socket pin 2 to pin stack 20. Socketed the UniBIOS, and went through and checked for continuity from each pin of the UniBIOS down to the original BIOS pin going into the board. All is good.

    But when I power on the MVS I get the garbled screen that says SOMETHING IS WRONG. Is this the wrong install method for this board, the MV-1A? I know the MV-1C is a different install, with a surface mount BIOS chip and an install that isn't 1 to 1 with the BIOS pins. Can the UniBIOS not be installed on an MVS board with this piggyback method? I'm at a bit of a loss here, everything looks good but the UniBIOS isn't working. Any input would be really appreciated!

    Install pic 1

    Install pic 2

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    Just desolder it all off and install a fresh socket. That will also give you a good view to test all of the traces while it's off. I wouldn't even bother with any piggybacking.

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    ^. Even if there aren't going to be more updates, doing a socket install is a far superior way to install a new bios. More problems arise from the piggyback method than the time it saves going that route.

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    Quote Originally Posted by NexusX View Post
    Just desolder it all off and install a fresh socket. That will also give you a good view to test all of the traces while it's off. I wouldn't even bother with any piggybacking.
    The traces are all fine, the board was powering on and giving the crosshatch test.

    I desoldered the bios in my AES and installed a socket, thought it wasn't an ideal process. Lacking a desoldering pump, the easiest way to get the existing bios out in my situation is snip the legs and pull what's left of each pin out of the PCB one by one. If nothing else works I could resort to that, but I really hate destroying the original bios chip like that. Not that it really matters, I suppose, since there's no reason to go back to a stock bios, but it feels like destroying a piece of history or something.

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    Quote Originally Posted by King of Dirt View Post
    The traces are all fine, the board was powering on and giving the crosshatch test.

    I desoldered the bios in my AES and installed a socket, thought it wasn't an ideal process. Lacking a desoldering pump, the easiest way to get the existing bios out in my situation is snip the legs and pull what's left of each pin out of the PCB one by one. If nothing else works I could resort to that, but I really hate destroying the original bios chip like that. Not that it really matters, I suppose, since there's no reason to go back to a stock bios, but it feels like destroying a piece of history or something.
    Spend $20 on a heat gun and you can lift the Bios chip right out of the board without damage. And a desolder pump costs about $5. It's worth the investment.

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    Quote Originally Posted by NexusX View Post
    Spend $20 on a heat gun and you can lift the Bios chip right out of the board without damage. And a desolder pump costs about $5. It's worth the investment.
    I have a hot air gun, and a hot air station. The hot air gun gets a bit too hot for my preference, but I'll bust out the hot air station and give it a go when I have some time. I'm assuming it would be best to apply the heat from the back side of the board, away from the rest of the surface mount components that might desolder as well.

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    you can cut off old bios legs or. as i have done, you can use a vacuum pump or a desolder gun with vaccum and suck off the tin from pins,from bottom side, if it will remain some tin, you can use hot gun on the top side of the board to liquify the remaining tin pins and remove the chip .

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    Just for reference, I got the piggyback working. Per some suggestions on another forum, I reflowed the solder work on all of the legs just to be sure of the connections and continuity, and I routed pin 2 of the socket to the PCB connection where pin 2 of the bios chip was lifted from.

    WE GOT CROSSHATCH

    Thanks for the input, I do appreciate it!

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    Quote Originally Posted by King of Dirt View Post
    I'm assuming it would be best to apply the heat from the back side of the board, away from the rest of the surface mount components that might desolder as well.
    I have had more luck putting heat on top of the bios chip pins directly in a back and forth motion while gently lifting the chip away with tweezers. That hits just the pins and solder with heat first instead of having to heat the entire back side of the board and any surface mount components stay on because the parts side is still upright.
    Last edited by NexusX; 05-20-2020 at 02:57 PM. Reason: typo

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    Quote Originally Posted by pier View Post
    you can cut off old bios legs or. as i have done, you can use a vacuum pump or a desolder gun with vaccum and suck off the tin from pins,from bottom side, if it will remain some tin, you can use hot gun on the top side of the board to liquify the remaining tin pins and remove the chip .
    Quote Originally Posted by NexusX View Post
    I have had more luck putting heat on top of the bios chip pins directly in a back and forth motion while gently lifting the chip away with tweezers. That hits just the pins and solder with heat first instead of having to head the entire back side of the board and any surface mount components stay on because the parts side is still upright.
    I think there's some good advice on methodology in both of these posts. If I end up messing around with more MVS or AES units hopefully I'll have a chance to put it to use!

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