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?

      Hey everyone, this is going to be an interesting first post. I've lurked around here for a while, and a lot of the advice and information has been really helpful in getting my Neo Geo AES working and upgraded (especially the AES RGB bypass with THS7314 RGB amp, the RGB out from my AES looks incredible now). 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 product code used for the Chinese market.

      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. I posted this same problem over on the tech support forum on Neo-Geo.com, and it was met with the blanket "don't piggyback, install a socket" response I figured I'd get. Like I mentioned there, my current rework setup isn't ideal for desoldering components like the NG bios chip; when I did it in my AES, I was fixing a lot of bad work I did about 15 years ago and ended up snipping all the legs to get the chip off, then removing each pin individually. It's not a great method, but it works, though I don't like the feeling of destroying the original bios chip. NO SIR I DON'T LIKE IT.

      Here are some pics of the piggyback install:

      Install pic 1

      Install pic 2


      I was looking at the datasheet of the TC531024P-15 chip used for the NG bios, and wrapping my head around the lifted pins and the stacks they're connected to. Pin 2 is Chip Enable, and when it's pulled high it's disabled (hence the 15K resistor to the +5v pin stack at 40) and when it's pulled low it's enabled (which is why pin 2 of the piggybacked socket is connected to the pin 20 stack, which is Output Enable and also pulled low to be activated). So the combination of the high pull 2/low pull 20 on the original bios and low pull 2/low pull 20 on the piggybacked socket disables the original bios and enables whatever is plugged into the dip socket.


      Why is this not working, then? Are there all kinds of other issues getting a piggyback to work? Or is it just possible that I have a bad burn of the UniBIOS on this eeprom? I'll pull the one I know is working from my AES tomorrow and test it out, make sure it's not something as simple as that.

      But any other input would be greatly appreciated, I'd like to get this consolized MVS wrapped up. Thanks for reading/helping with my first post!

      The post was edited 1 time, last by King of Dirt ().

    • King of Dirt wrote:

      It's not a great method, but it works, though I don't like the feeling of destroying the original bios chip. NO SIR I DON'T LIKE IT.
      Is that BIOS different than the JAP/US/EUR ones? I have piles of them. I agree with you not wanting to destroy the OG chip but you don't seem to have many options with the tools you have. Plus you already clipped pin 2.

      King of Dirt wrote:

      Or is it just possible that I have a bad burn of the UniBIOS on this eeprom? I'll pull the one I know is working from my AES tomorrow and test it out, make sure it's not something as simple as that.
      Could very well be.
      Looking for:
      - faulty Hang-On, Space Harrier or Enduro Racer (2203 sound board)
      - Sega Mega-CD 1 power board
      - Super Nintendo CPU (3 needed)



      "I'd 1cc games but I have a real life."
      01010011 01000101 01000011 01010010 01000101 01010100 00100000 01001101 01000101 01001110 01010101 00100000 01000111 01010101 01011001
    • Apocalypse wrote:

      Is that BIOS different than the JAP/US/EUR ones? I have piles of them. I agree with you not wanting to destroy the OG chip but you don't seem to have many options with the tools you have. Plus you already clipped pin 2.
      This is true, pin 2 is clipped and that bios is now screwed. I'm not entirely certain if it's a different bios specific to the Chinese region; my guess is it's probably just the Japanese bios, or maybe it defaults to the European one. I'm not really sure, I got this board on a lark and I don't have any MVS carts at the moment to boot and see what it defaults to.

      But I also have a heat gun and a hot air station, so I could just blast the bios on the solder side for a bit and lift it out of the board, I suppose. That would probably be the best option at this point, get it out and fit in a new socket (provided the UniBIOS I have isn't faulty, of course).
    • King of Dirt wrote:

      Install pic 1

      Install pic 2
      Sorry for the bad comment but I don't like that soldering. did you add some flux?

      I agree with @Apocalypse and I think that the best is jut to put a socket and do the tests on that one, no piggybacking.
      * Arcade-projects, the site where you get the most of your arcade games.
      * If you want Drama go to Neo-Geo forum ---Darksoft
    • Darksoft wrote:

      Sorry for the bad comment but I don't like that soldering. did you add some flux?

      stj wrote:

      what a mess, you need to link pin2 of the socket to hole2 on the board - dont go re-aranging shit.
      Duly noted. I slapped some more flux on and reflowed all the connections this morning, just to make sure. There was continuity before, but it never hurts to be too careful. And I routed pin 2 of the socket to the PCB hole 2 from the lifted leg, and...

      IT LIVES

      Thanks for the help, everyone, I really do appreciate it. I was using the piggyback instructions from the UniBIOS site, but now that I think about it those are probably AES specific and might not be applicable to MVS boards and their specific pinout for the bios chip.

      Just glad to have it up and running so I can keep on with this project!