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Thread: NGCD cd drive pcb question

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    NGCD cd drive pcb question

    Hi all,

    I just got a Neo Geo CD that didn't read discs. After close inspection I saw that something on the CD-drive board was burnt. It was a transistor in DPAK package labelled D1758. I've basically replaced this and retraced some burnt traces around it. There's also a diode next to it that looks burnt as well (I've checked with the multimeter and it definitely looks blown). The thing is I don't know what kind of diode should I be looking for as a replacement. On the PCB, the diode is labelled as ZD101, and the diode itself has a "J2" written on top (see the pic of another ngcd that I have). I've done some research but I haven't found any info relating to this "J2" nomenclature. I assume it's a zener? Could anyone please give me some more info on what I should buy to replace it? I'm not really familiar with types of diodes. Thanks very much!ngcd diode.jpg

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    Cheng's Errand Boy
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    Well you'll need a spec sheet for the Zener diode which I can also look for, but buying the exact same or equivalent diode will work. Make sure its a Zener diode as those allow current to pass both directions.

    Edit: Can't find a damn thing. I need to know at least a voltage rating or something.. I guess if you can figure out the limits of whatever the power is going to through that diode we could figure out a replacement
    Last edited by DasiyAge; 05-12-2019 at 04:27 PM.

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    Cheng's Errand Boy
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    Can we get a pic of the diode as well or is it too late?

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    Hi there, thanks so much for your reply.

    I attached a pic of the diode to my first message. It looks a bit blurry, but there's a "J2" on top of it. To me, it looks like a SOD123 package. I could try measuring the voltage that gets into that. I'll try that later on the day, when I'm back from work. These last couple of days I've kept looking for components with the "J2" marking, and I came up with a Vishay MMSZ5247B. This is a 0.5W, 17v diode. I don't know if this voltage is too high though for what's in that cd board. Since I have no schematics, it's really hard to tell. If you want to take a look at the datasheet, it's here: https://www.vishay.com/docs/85774/mmsz5225.pdf

    Do you think this could be the one?

    Thanks in advance

  5. #5
    Cheng's Errand Boy
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    The markings of the diode you list come up as "!J2 S" which is pretty close. The important thing to find out is what the max voltage to the CD laser (or whatever component is downstream of the diode) is because you need a diode that will fault and reverse breakdown at that maximum so that excess current doesn't damage the component. I will reach out to some other members who may have knowledge of this. Also some sort of schematic or service manual for the NGCD would be helpful. Last bit of info I need for now is what model do you have? Top loader or front loader CD? Or CDZ?

    Edit: I would trace a continuity path as well as seeing what voltage goes into the diode. That way if we know what it goes to we can look up the schematics for that part(s)
    Last edited by DasiyAge; 05-13-2019 at 09:12 PM.

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    Hi again DaisyAge, thanks for the interest and sorry for the delay in replying but I couldn't find the moment to check this.

    So the voltage that goes into the diode is 9v. This is a top loader NGCD. It doesn't seem like a SOD123 as I said though, the package is smaller than that, maybe a SOD323. Regarding the schematics or service manual, I couldn't find anything of the like, especially the CD board.

    Thanks again.

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