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Thread: NeoGeo Time going untra fast / speeding.

  1. #1
    Divine Hand of the UniBIOS
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    NeoGeo Time going untra fast / speeding.

    I have an intermittant fault coming on my MV1-FS. It seems that sometimes the time goes into overdrive and is speeding along like no tomorrow.

    Anyone else seen this problem and if so is it an easy fix? While it speeds this way does it also drain the backupRAM battery quicker?
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    Benimaru's Hairdresser
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    Bad UPD4990 or 32.768kHz crystal?

    https://wiki.neogeodev.org/index.php?title=UPD4990
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    Divine Hand of the UniBIOS
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    I'm not sure its the crystal as when this is happening if I set the time in test mode it will stop. Could defo be the 4990... I'm really intrested to know if others have seen this situation and what they did to fix it.
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  4. #4
    Street Hoop Star
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    This use to happen to my MV1C, before it died of probably unrelated causes.

    I would just clear backup ram or turn it off and remove the battery and reinstall it and it would clear it up.

  5. #5
    Maxima's Barber
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    I have this same issue on an MV1FZ, I have just ignored it TBH.

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    Divine Hand of the UniBIOS
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    Good to know others have seen the same thing also. Would be good to know exactly what the issue is here. It will have an effect on some games that use the calander.
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  7. #7
    Stupid Bitch.
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    My 4 slot does this... doesn't seem to really affect anything but the calendar for bookkeeping...

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  9. #9
    Divine Hand of the UniBIOS
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    Quote Originally Posted by Xian Xi View Post
    iirc it's the 4990
    Thanks, if the 4990 is faulty in this state do you know if it takes extra power from the battery when the system is powered off?
    Last edited by Razoola; 02-04-2018 at 03:39 AM.
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  10. #10
    SouthTown StreetSweeper
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    This used to happen to my 4 slot. I put a fresh battery in the coin cell holder, set the time and it's be fine every since.
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  11. #11
    Divine Hand of the UniBIOS
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    Quote Originally Posted by pulstar View Post
    This used to happen to my 4 slot. I put a fresh battery in the coin cell holder, set the time and it's be fine every since.
    Hmmm, I wonder is this possibly means the 4990 (older spec) goes into this state when the battery is flat until the time is manually set again?
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  12. #12
    Lazy SNK Employee

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    I've had that happen a few times also. I didn't take precise notes but I remember that when probing the crystal pins with a scope, it stopped oscillation.
    The battery voltage was below 2V and just replacing it got it to count seconds correctly again (and probing the crystal again showed a clean sine).

    I thought the 4990 wouldn't get the configuration bits correctly and set TP to 64Hz instead of 1Hz, but it seems that TP is only used during the startup self-tests, not in the bios menu ?
    Maybe a more plausible cause would be the crystal oscillator giving a distorted signal when the voltage is too low, so the 4990 starts counting on overtones ?

  13. #13
    Divine Hand of the UniBIOS
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    Im my case at least there could be an issue with undervoltage as far as the battery is concerned. I'm currently waiting on some replacement batteries in the post.
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    Divine Hand of the UniBIOS
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    I have had the replacement CR2032 battery on my MV-1FS for a good few days now and so far the speeding time issue has not happened again. I think there could be some truth in undervolt being the issue.
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  15. #15
    Maxima's Barber
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    Quote Originally Posted by Razoola View Post
    I have had the replacement CR2032 battery on my MV-1FS for a good few days now and so far the speeding time issue has not happened again. I think there could be some truth in undervolt being the issue.
    Nice I'll give that a try on my MV1-FZ too and report back. I think I have a spare coin cell holder around here somewhere..

  16. #16
    Maxima's Barber
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    OK so I replaced the dead battery on my MV1-FZ with a battery holder and CR2032 coin cell using the JNX guide.

    I can confirm this has resolved the ultra fast clock issue for me too!

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