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Thread: Neo Geo AES csync low? (RESOLVED/FIXED)

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    Great Puma (Level 12) Bratwurst's Avatar
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    Default Neo Geo AES csync low? (RESOLVED/FIXED)

    I have one of the early iterations of the Neo Geo AES that on bootup only shows a black screen and was previously mute.

    Bit of a long shot but does anyone around here know if pin 126 of the LSPC-A0 chip should be showing 5 ohms of resistance to ground? On replacing the CXA1145 video encoder chip, I can now get sound but still no video, and I measured csync input at 0.4 volts which seems kind of low for what pin 10 of the CXA1145 is expecting.
    Last edited by Bratwurst; 05-17-2019 at 10:11 PM.

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    ServBot (Level 11) Niku-Sama's Avatar
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    I dont have any experience with a AES but in general it sounds like you have a short some where...
    I get the feeling you already know that though.

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    Great Puma (Level 12) Bratwurst's Avatar
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    It looks like the LSPC-A0 is faulty, but I have no other system on hand to reference. Worst case scenario is rob the part from an early MVS unit.

    I'd also like to know if the RGB channels before they go into the CXA1145 (pins 2, 3 and 4) are supposed to be 0.7vpp or if they should be stronger. Curiously this replacement chip isn't outputting the RGB on the other side (just like the original, which was confirmed faulty) and the specsheet insinuates it's just a passthrough, so I have more CXA chips on the way.

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    Great Puma (Level 12) Bratwurst's Avatar
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    I hope this information may be helpful to others in the future which is why I'm posting a followup. I was able to source a battery corroded MV1 board and determined that csync is normally 5 M ohms to ground pin on the LSPC-A0, and should NOT be 5 ohms as it was on the faulty AES. So I performed a transplant:





    The Neo Geo AES now works as it should. So my suspicion is someone plugged or unplugged a video cable into the system while it or the display was on, or there was a power surge- bridging the audio output and csync input of the CXA encoder. Which bled into the LSCP-A0 chip's csync output pin and eventually shorted it to ground.

    Video of the now fixed system in action:

    https://www.youtube.com/watch?v=leMB9AX9v-Q&

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