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Thread: Rusted out ZMC2

  1. #1
    Morden's Lackey
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    Rusted out ZMC2

    Any advice on this one? Boots into game, some graphics just show as large solid blocks. The ZMC2 has a leg that's completely rusted. I don't think I can get wire on it, there's nothing left and the pads look pretty bad around that area.

    Diagnostic rom all regular test pass. Z80 test shows error expected C3 actual 00.


  2. #2
    H = Heinously
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    About all you could do is get a micro file and sand away at the plastic housing of the chip to expose more of the remnants of the missing leg. Not like there's much to lose in potentially damaging the chip. Some of the other rusted pins look like their traces go under the chip, they may be ok. It does appear one of the pins is supposed to go a short distance away from the chip to a via throughhole, you can see one that isn't rusted near it.

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    Crossed Swords Squire
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    For rust I usually start with white vinegar and a hard bristle toothbrush to get the bigger pieces of rust off and to make any other reactions inert. I second the micro file idea as there's not much else you can do in that case. If you have deoxit I'd recommend using that in conjunction with the vinegar and hope most of the rust comes off. Worst case grab a beater board and swap the ZMC2

  4. #4
    Morden's Lackey
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    Quote Originally Posted by DasiyAge View Post
    For rust I usually start with white vinegar and a hard bristle toothbrush to get the bigger pieces of rust off and to make any other reactions inert. I second the micro file idea as there's not much else you can do in that case. If you have deoxit I'd recommend using that in conjunction with the vinegar and hope most of the rust comes off. Worst case grab a beater board and swap the ZMC2

    I don’t have deoxit, but that pic is after a toothbrush + white vinegar wash. I didn’t want to go too hard. I will probably try to grind away some of the chip to expose more of the leg.

  5. #5
    World Hero
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    Quote Originally Posted by Jeffpin View Post
    I don’t have deoxit, but that pic is after a toothbrush + white vinegar wash. I didn’t want to go too hard. I will probably try to grind away some of the chip to expose more of the leg.
    You may have to remove the chip entirely and see if there is any further corrosion under the chip. The pin that rusted off is related to the audio section, not graphics. This is why the z80 test was failing in addition to the graphics issue.

  6. #6
    Kuroko's Training Dummy
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    If this helps, I have a shit-ton of ZMC2s laying on a shelf. I can send you one, just pay shipping. PM if interested.

  7. #7
    Morden's Lackey
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    Quote Originally Posted by defalt View Post
    If this helps, I have a shit-ton of ZMC2s laying on a shelf. I can send you one, just pay shipping. PM if interested.
    That would be awesome, PM incoming.

    I managed to remove the chip, it looks pretty rough underneath. Some pads might be missing.

    Where can I find a pin out / schematic so I can test the traces from the pads?

  8. #8
    Crossed Swords Squire
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    NeoGeo Development Wiki is your friend here, https://wiki.neogeodev.org/index.php?title=NEO-ZMC2

  9. #9
    Morden's Lackey
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    Quote Originally Posted by DasiyAge View Post
    NeoGeo Development Wiki is your friend here, https://wiki.neogeodev.org/index.php?title=NEO-ZMC2
    I’m starting to piece together info from there. The schematics are hard to read. I’m new to using a logic probe. How do I know if a leg should be hi, lo, or pulse?

  10. #10
    Crossed Swords Squire
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    I don't know, I'm not well versed with logic probes either

  11. #11
    Morden's Lackey
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    I have a better understanding after watching this: https://www.youtube.com/watch?v=7l039y8dX5A

    However, it still requires the knowledge of the internal workings of the chips to know the inputs/outputs and whether the logic is correct.

  12. #12
    Another Striker
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    On the dev wiki, the image of the chip shows the inputs and outputs of the IC. The pins with the arrow/triangle that point in are inputs, the ones that point out are outputs. In the case of the ZMC2, the green input pins (C0-C31) are the incoming sprite data, the ZMC2 transforms that data and it pops out the green output pins (GAD/GBD0-3). All of these pins should be pulsing.

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