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Thread: How to test the M2-atx psu

  1. #1

    How to test the M2-atx psu

    I have installed it in vehicle, and it basically doesn't work.
    I have connected permanent 12V, Switched 12V and Ground. MB switch also.
    No jumpers, in dumb psu mode (maybe a case of dumb operator mode!!)
    Connected to the motherboard and all I get is 12V from the atx connector, no 5V or 3.3V on the rails.
    I read the manual..... and the 5V rail should be first to come on when ignition is switched on!

    Anyone have a clue as to whether it's me who's being a little thick or whether it sounds faulty!

    Any help appreciated. Thanks
    Nygie

  2. #2
    Advanced Member
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    if i remember correctly, the VERY FIRST TIME the m2 is used you have to manually power up the motherboard with the power switch. thereafter, ti will happen automatically.

    i may be mistaken though, but i remember something like that being wirtten here.

  3. #3
    Quote Originally Posted by warren View Post
    if i remember correctly, the VERY FIRST TIME the m2 is used you have to manually power up the motherboard with the power switch. thereafter, ti will happen automatically.

    here.
    How do you mean manually power up the motherboard, I shorted across the MB switch wires if that's what you mean.? That should work as it's just a push to make switch isn't it!
    Thanks

  4. #4
    Advanced Member ElKeeed's Avatar
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    Have you connected the power switch cable the right way round? Polarity matters.

  5. #5
    I was under the impression the MB switch connector is voltage free as all you have to do is short the two pins together to get the MB to fire into life, so polarity shouldn't matter in this case. Should it?

  6. #6
    Advanced Member Rob Withey's Avatar
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    Yes, polarity matters. You are assuming way too much about the circuitry of the m2atx that actually closes the switch.
    Building new system using BeagleBoard and modified VWCDPIC.

    Car PCing since 1999.

  7. #7
    Hmm funny that, as it is just normally a push to make no voltage need switch.
    I have found the problem, it is the switch keeping the motherboard off, if I leave the switch lead on then it will not boot. If I short the lead to MB it boots fine, but if I reattach to the m2-atx it shuts down the PC. Which seems to indicate a fault of being permanently shorted together! I have not tested this theory I was just chuffed to get it working. I think I will just put a push switch somewhere to start/shutdown manually.

  8. #8
    Advanced Member Rob Withey's Avatar
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    Quote Originally Posted by Nygie View Post
    Hmm funny that, as it is just normally a push to make no voltage need switch.
    I have found the problem, it is the switch keeping the motherboard off, if I leave the switch lead on then it will not boot. If I short the lead to MB it boots fine, but if I reattach to the m2-atx it shuts down the PC. Which seems to indicate a fault of being permanently shorted together! I have not tested this theory I was just chuffed to get it working. I think I will just put a push switch somewhere to start/shutdown manually.
    You are still assuming too much. The circuitry on the m2atx is likely not a simple switch. Typical implementation of the power switch on a motherboard is a signal line with pull up resistor and a ground line to connect that signal to. The power switch is connected between those lines, and when the switch is open the line is pulled high by the pullup resistor, and when the switch is closed the line is switch to ground.

    The implementation on the power supply side is often to draw one line to ground, not short the two pins together. The lead that you connect to the power supply has one line permanently at ground, and the other is shorted to ground either via a fet or an open collector npn bipolar transistor. (I chose the latter when implementing this on my power supply's shutdown controller).

    If you get the polarity of the lead the wrong way around, what you end up with is the power switch permanently closed, since the ground line from the power supply holds the switch signal line on the motherboard low. The switched line from the power supply will switch the motherboard ground line to ground, which has no effect.

    I hope that clears up your simple assumption that the m2atx switching the power switch is a simple, non polarised switch...!
    Building new system using BeagleBoard and modified VWCDPIC.

    Car PCing since 1999.

  9. #9
    Moderator rustyboxx's Avatar
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    You know too much!



    I may have to kill you

  10. #10
    I wish I knew as much. Thanks for the lesson, which for some strange reason I understand. But still doesn't change things as I tried it both ways. I will just use it manual for now.
    Thanks

  11. #11
    How strange, it is working totally as it should now!
    Spoooky

  12. #12
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    i told you so.

    it needs one proper power up to get it going.

    :-)

  13. #13
    thanks

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