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  1. #1

    MKL's Avatar
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    The audio issue of AES revision 3-4

    A few years ago, after buying a system from me, the customer (who considered himself an audiophile) complained that he could hear a buzzing noise coming from his TV speakers as well as from the headphone jack. He also mentioned that he had a low serial system that didn't have that issue at all.

    Since I had another (unmodded) system with the same PCB revision (3-4), I tested it immediately and much to my surprise it was having the same issues described by the guy. I couldn't believe I had never noticed it because once it was pointed out to me it was impossible not to hear it.

    To get a better grasp of the problem I ran tests with as basic a setup as possible: I ran the system without hooking up video, only with headphones plugged in and another system (revision 3-6) running next to it, also with only headphones in and only the 3-4 was having the buzzing issue. Both system were powered by the same power supply (without step-down transformer) so the PSU was ruled out as a possible cause.

    When the guy sent the system back to me along with his other "silent" system (that turned out to be the very first PCB type NEO-AES) the tests confirmed that 3-4 had the issue and that NEO-AES was buzz-free just like 3-6. The thing was all the more puzzling as NEO-AES and 3-4, despite being different revisions, have the same audio circuit (while on revisions 3-5 and 3-6 it's partly different).

    I was starting to put the blame on the different PCB layout of the 3-4 causing interference when I noticed the difference between the NEO-AES and 3-4 circuits: each audio IC (DAC, op-amps, headphone amplifier) on the NEO-AES has a decoupling (bypass) cap nearby (close to the VCC and GND leads) just like all the other ICs on the board which is what you would normally expect to see:



    http://img404.imageshack.us/img404/9035/27727951.jpg

    The 3-4 system doesn't have them though. Not a single bypass cap in sight:


    http://img404.imageshack.us/img404/116/30702199.jpg

    After adding 0.1uF (104 marking) caps across the 5V and ground leads of each IC (on the bottom of the board) the issue was gone:



    The cap for the DAC (YM3016) seems to make the most difference.

    According to the datasheet, the bypass cap recommended for the headphone amplifier IC is a 100uF electrolytic cap.
    The value for this cap on MVS boards is 470uF/16V. I used 100uF/35V:




    Of course you will have noticed the 1000pF (marking 102K) caps soldered to pin 1 and 16 of the IC. Those are other components that SNK left out of the headphone circuit on AES boards but they're supposed to be there according to the datasheet (they are part of a low-pass filter on the inputs) and are not missing from MVS boards:

    http://img189.imageshack.us/img189/4275/46690809.jpg

    A further example of the lack of attention in designing the audio circuit on this revision is the incorrect placement of two polyester caps in the L channel path:


    http://img339.imageshack.us/img339/9559/84792566.jpg

    To rectify things desolder and swap them.

    How about the other revisions? Will 3-3 have the same issue as 3-4? I didn't have the chance to test one but judging by the lack of bypass caps for the audio ICs it's safe to assume it has the issue too:



    I mentioned above that revision 3-6 is buzz-free. Let's take a look at the audio circuit of this board:


    http://img683.imageshack.us/img683/8319/48387903.jpg

    In this case the caps used for decoupling purposes are electrolytic instead of the usual multilayer ceramic ones. They're the 10uF caps numbered 1, 3 and 9 in the previous pics.

    Revision 3-5 is almost identical to 3-6 but guess what, the bypass cap for the DAC (number 1 on 3-6) is missing:



    I haven't tested a 3-5 system so I can't tell if the missing cap makes any difference.

    It may be worth mentioning here that the headphone out on revision 3-6 has the R and L channels reversed. I had noticed this years ago and wasn't the only one:

    http://www.neo-geo.com/forums/showthread.php?t=94456

    Since then I have found why. It's another mistake of good ol' SNK designers. Apparently they realized it and made a correction on later boards by moving a couple of resistors:

    Last edited by MKL; 05-17-2010 at 05:56 AM.

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  3. #3
    Tung's Hair Stylist
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    Very cool. This deserves a sticky or wiki entry. I'm sure this is going to help a lot of Neo Geo owners who didn't have a fix for this. Awesome work.

    ~Anselm~

  4. #4
    monouchi
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    Yeah, thanks for that awesome post.
    Great info.

  5. #5
    monouchi
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    Quote Originally Posted by MKL View Post
    After adding 0.1uF (104 marking) caps across the 5V and ground leads of each IC (on the bottom of the board) the issue was gone:


    So to fix it, this is what needs to be done.
    Or should I add the cap for the DAC (YM3016) too?

    Also, where can one find these caps and what voltage on them should it be?

    Thanks.
    Last edited by monouchi; 05-17-2010 at 05:24 AM.

  6. #6

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    Quote Originally Posted by monouchi View Post
    So to fix it, this is what needs to be done.
    Or should I add the cap for the DAC (YM3016) too?
    Yes, that's what needs to be done and it's enough to get rid of the issue:

    http://img404.imageshack.us/img404/149/31157064.jpg

    The DAC is in the upper right part of the pic and it has a 0.1uF cap soldered across pin 1 and 2.

    In the blank space there is the 4558 op-amp for the mono output on the A/V port. You can put a cap on that too while you're at it (although I seem to understand you're not using the mono out).

    Quote Originally Posted by monouchi View Post
    Also, where can one find these caps and what voltage on them should it be?
    If you're referring to the electrolytic cap in this pic, that's on the headphone amp 2066D and it's 100uF/35V. The voltage rating isn't important here, 16-35V is OK and the size won't be excessive (on MVS boards it's 470uF/16V). But if you don't have one handy, a 0.1uF caramic cap (as shown in the first pic) will be enough: it's what you find on the buzz-free NEO-AES revision:

    http://img571.imageshack.us/img571/7678/78002479.jpg

    Any electronics store will have these capacitors. If you can't find them locally you have plenty of online options, for instance:

    http://search.digikey.com/scripts/Dk...me=490-5401-ND
    http://search.digikey.com/scripts/Dk...&name=P5551-ND

    Note that electrolytic caps are polarized so you need to solder the positive lead to the 5V pin of the IC and the negative lead to the ground pin. For ceramic caps it doesn't matter.
    Last edited by MKL; 05-17-2010 at 08:41 AM.

  7. #7
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    Great info MKL!

  8. #8
    monouchi
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    Super thanks MKL.

  9. #9
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    great post. My AES is not 3-4 but I always use the headphones and a buzz like that would be extremely irritating if I had to put up with it. will keep a tab on this incase I ever get another AES..

  10. #10
    JammaNationX
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    Quote Originally Posted by MKL View Post
    It may be worth mentioning here that the headphone out on revision 3-6 has the R and L channels reversed. I had noticed this years ago and wasn't the only one:

    http://www.neo-geo.com/forums/showthread.php?t=94456

    Since then I have found why. It's another mistake of good ol' SNK designers. Apparently they realized it and made a correction on later boards by moving a couple of resistors:

    Hey MKL,

    So is it only the 3-6 that is reversed and not the 3-5 as well?

  11. #11

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    3-5 is ok

  12. #12
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    I could swear i could hear some buzzing through the headphones jack of my AES when i connected it to my stereo speakers. Gonna open it up and see what reveision it is. Its a jap system near the 50K serial number.

    However I aint too brave to do all this myself. Can I send you the board if some work needs to be done MKL?

  13. #13
    JammaNationX
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    Quote Originally Posted by MKL View Post
    3-5 is ok
    Cool. I think I modded one that was reversed, in fact I think it was the one that I made the tutorial with which is why the channels were switched. Played mind games with me.

  14. #14

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    Quote Originally Posted by Daytime_Dreamer View Post
    I could swear i could hear some buzzing through the headphones jack of my AES when i connected it to my stereo speakers. Gonna open it up and see what reveision it is. Its a jap system near the 50K serial number.

    However I aint too brave to do all this myself. Can I send you the board if some work needs to be done MKL?
    Yes. 50K can be expected to be either 3-3 or 3-4 and both are supposed to have the buzz issue.

    Quote Originally Posted by Xian Xi View Post
    Cool. I think I modded one that was reversed, in fact I think it was the one that I made the tutorial with which is why the channels were switched. Played mind games with me.
    I've posted pics of 3-5 and 3-6 so you can follow the traces from the DAC through to the headphone jack and see that they don't go to the same contacts on the jack: 3-5 is correct, 3-6 is reversed. Since this is due to a PCB layout mistake, I don't see how 3-5 could be reversed.

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  16. #16
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    Fully recapped with audio fix in place on a 3-4

    I just wanted to say thank you for sharing this information. My JPN 3-4 was loosing its audio so I decided to recap the main board when I found this thread so I recapped the board, used 470uf + 75-ohm for the RGB fix and then tested. Audio was back but the audio buzz was still present. I added the 5 .1uf caps to get rid of the audio BUZZZ . Yup it sure worked great. I used Fatal Fury 3 since the title screen is dead silent. After I added the 5 .1uf caps the buzz was gone and the audio crystal clear.

  17. #17
    Timid Neo Newbie

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    I hope it is ok to post this here! I am having a weird audio issue with my neo geo aes and am stumped as to what to try next. It is hard to explain so i made a video which you can view here http://www.youtube.com/watch?v=DZdJGw9GvNw

    Sometimes the audio works and sometimes it does what the video shows but i have never ever been able to hear the starting neo geo tune on system turn on.

    Any help would be appreciated and again if i shouldn't have posted this hear please delete this

  18. #18
    JammaNationX
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    Quote Originally Posted by nuker43 View Post
    I hope it is ok to post this here! I am having a weird audio issue with my neo geo aes and am stumped as to what to try next. It is hard to explain so i made a video which you can view here http://www.youtube.com/watch?v=DZdJGw9GvNw

    Sometimes the audio works and sometimes it does what the video shows but i have never ever been able to hear the starting neo geo tune on system turn on.

    Any help would be appreciated and again if i shouldn't have posted this hear please delete this
    You have some broken traces from the cart slot for sound. They need to be repaired. But if it only happens from time to time, it's most likely just a dirty slot.

  19. #19
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    Quote Originally Posted by Xian Xi View Post
    You have some broken traces from the cart slot for sound. They need to be repaired. But if it only happens from time to time, it's most likely just a dirty slot.
    Hi Xian, thank you for the reply. I just tried cleaning the slot with some alcohol and get the same results. It used to be from time to time i would get sound but now it does what the video does 100% of the time. It's weird because different games have different audio glitches. I tried looking for broken traces but could not find any. I found some traces where the lacquer is missing but i tested with the multimeter and they ohm out at 0. Should i try replacing the YM2610 sound chip?

  20. #20
    JammaNationX
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    Quote Originally Posted by nuker43 View Post
    Hi Xian, thank you for the reply. I just tried cleaning the slot with some alcohol and get the same results. It used to be from time to time i would get sound but now it does what the video does 100% of the time. It's weird because different games have different audio glitches. I tried looking for broken traces but could not find any. I found some traces where the lacquer is missing but i tested with the multimeter and they ohm out at 0. Should i try replacing the YM2610 sound chip?
    Hard to say, I would have to see it for myself to know what exactly is going on. It could be a chip, traces or something else.

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