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Thread: "NEOGEO-2" Schematic theory:

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    "NEOGEO-2" Schematic theory:

    So this may be already common knowledge, but after reviewing the schematics floating around on the internet:

    https://wiki.neogeodev.org/index.php?title=Schematics

    My friend Ste pointed out it cannot have been of the 3-6, even though the stereo audio channels are swapped in the schematic's headphone jack. This is because the composite video and csync pins are not tied together like they are in the 3-6. Additionally, I noted the output caps were set to 100uF and resistors at 68Ohms in the schematic.

    Now since we know the 3-3, 3-4, and 3-5 do not have inverted stereo channels, and since the schematic designates 100uF caps and 68 Ohm resistors, my conclusion is that "NEOGEO-2" is actually a schematic for the ultra-rare AES3-2 revision. Indeed this may be a clue as to why the 3-2 is so rare: They caught the channel swap mistake and quickly corrected it in the 3-3 revision. Of course, the only way to know for sure is for someone with an unmodded 3-2 to check the channel orientation. To date though, I've only found one board shot of a 3-2 on the Internet.

    Again, my apologies if this is common knowledge by now. I just thought it was quite interesting that the existing AES documentation turns out to be from the absolute rarest of revisions!
    Last edited by FBX; 02-16-2019 at 01:18 AM.

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    drunk downunder!
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    Y'know I was wondering the same thing last night! I was on the shitter and squeezing out a true redwood and I stopped and thought 'fuck! That schematic has gotta be different to my AES!'


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    Quote Originally Posted by FBX View Post
    So this may be already common knowledge, but after reviewing the schematics floating around on the internet:

    https://wiki.neogeodev.org/index.php?title=Schematics

    My friend Ste pointed out it cannot have been of the 3-6, even though the stereo audio channels are swapped in the schematic's headphone jack. This is because the composite video and csync pins are not tied together like they are in the 3-6. Additionally, I noted the output caps were set to 100uF and resistors at 68Ohms in the schematic.

    Now since we know the 3-3, 3-4, and 3-5 do not have inverted stereo channels, and since the schematic designates 100uF caps and 68 Ohm resistors, my conclusion is that "NEOGEO-2" is actually a schematic for the ultra-rare AES3-2 revision. Indeed this may be a clue as to why the 3-2 is so rare: They caught the channel swap mistake and quickly corrected it in the 3-3 revision. Of course, the only way to know for sure is for someone with an unmodded 3-2 to check the channel orientation. To date though, I've only found one board shot of a 3-2 on the Internet.

    Again, my apologies if this is common knowledge by now. I just thought it was quite interesting that the existing AES documentation turns out to be from the absolute rarest of revisions!
    I am sure you are right! Just based on the fact it has differences to the actual 3-6 boards out there.
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    Quote Originally Posted by lachlan View Post
    I was on the shitter and squeezing out a true redwood...
    Did it reach the surface of the water before full exit?

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    Yamazaki's Pupil

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    Quote Originally Posted by FBX View Post
    Did it reach the surface of the water before full exit?
    You're assuming he's finished

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    drunk downunder!
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    Look sometimes you gotta lift your left and right butt cheeks in a 3-2 configuration to get a full exit.


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    A more obvious reason why it cannot be the 3-6 schematics is the fact that the audio circuit is remarkably different (no NJM2066D on 3-6). It cannot be the 3-4 schematics either as the 3-4 has a dual power supply circuit (with or without LM2576 voltage regulator). I see no evidence that those schematics are of the 3-2 and not of the 3-3. The clue that they could be of the 3-2 because of an alleged mistake in the audio circuit is very weak as we know SNK didn't redesign a whole new motherboard revision when they made that mistake on the 3-6. They simply swapped two resistors.

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    Quote Originally Posted by MKL View Post
    A more obvious reason why it cannot be the 3-6 schematics is the fact that the audio circuit is remarkably different (no NJM2066D on 3-6). It cannot be the 3-4 schematics either as the 3-4 has a dual power supply circuit (with or without LM2576 voltage regulator). I see no evidence that those schematics are of the 3-2 and not of the 3-3. The clue that they could be of the 3-2 because of an alleged mistake in the audio circuit is very weak as we know SNK didn't redesign a whole new motherboard revision when they made that mistake on the 3-6. They simply swapped two resistors.
    Fair points. Indeed my speculation of the rarity of the 3-2 is likely not the case, and more likely that the 3-2 was made purely as an in-house prototype based on these schematics. However, there are plenty of circumstantial points to be made that these schematics were the bases for the 3-2: The date written in the drawings is well after the first AES release, the "NEOGEO-2" designation, and your own note about the 3-4 already having a different power configuration. It seems to me unlikely these schematics were meant for the 3-3 given the board pics of the 3-2 already posted in these forums. The board is pretty much identical to the 3-3 and given the schematics' designation of "NEOGEO-2", it would certainly make more sense that the 3-2 was the first to be based on these schematics.
    Last edited by FBX; 02-16-2019 at 09:48 AM.

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