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Discussion in 'General Electronics Discussion' started by Mubs, May 6, 2010.

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  1. Mubs

    Mubs

    8
    0
    May 6, 2010
    Hey Guys,
    First post, and wanted to say what a great forum this is!

    I'm making a mini-ITX PC and want to rip the 100w psu out of an old xbox 1 as it is small, fanless and has a 20 pin atx connector.
    The only problem is, it doesn't have a standard ATX connector as all of the pins are jumbled up as shown in the diagram below:

    [​IMG]

    remapping the pins shouldn't be a huge problem but the connector doesn't seem to have a -12v or a -5v rail.

    Done a bit of googling and i know i need either the max232, LM7915, or a voltage/switching regulator but can't make anything out as i'm finding it tough to understand some of the tech talk.

    as far as i can understand, the max232 wont work as it only gives out 10mA right?

    also, the xbox connector only has 2 x 3.3v rails whereas i'll need 3 for the pc atx connector.
    is it just a simple case of running another cable alongside one of the 3.3v rails in parallel?

    Would appreciate it if somebody could advice me on how to proceed.

    Kind regards,
    Mubs
     
    Last edited: May 6, 2010
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,271
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    Jan 21, 2010
    Don't try it. Get a proper power supply for your board.

    However if you really want to go ahead with this...

    For the 3.3V rail, you could probably get away with just 2 of the 3 leads connected. They're all in parallel and I'm sure the mini-ATX board requires less than the maximum power from the 3.3V rail (as compared to larger more power-hungry boards)

    the -5V rail is optional, or even removed from the spec, so you *may* be able to do without it. Does the motherboard documentation indicate a requirement for certain current from this rail?

    The -12V rail was traditionally for RS232, and I'm not aware of anything else that used it (although I've never looked in great detail). Your board *may* work without this rail.

    Then again, your board may check the voltages on these rails and refuse to start without them within spec.
     
  3. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    Some audio amps use -12V. Depending upon what audio amp that particular board uses, it may or may not be used.

    These days many boards use an integrated RS232 chip that generates the negative voltage on-chip (like the MAX232) so they may not use the -12V either.

    All that said, I would agree with Steve that you should get the right power supply. All it will take is one mistake due to lack of paying attention or lack of understanding and you could loose both the power supply and the motherboard.

    Worse than that, if the power supply does not have enough capacity, it may work most of the time and you may find that programs are crashing unexpectedly. You will invariably blame the software and the installation and waste months chasing a software and installation bug when the real problem was the power supply.

    ---55p
     
  4. Mubs

    Mubs

    8
    0
    May 6, 2010
    Thanks for the comments guys.
    if the only risk is the PSU not being able to supply enough juice then i may just go through with this...
    all the reviews of my board have rated it at between 35-45w under load.
    its the ASUS AT3N7A-I ION with intel atom 330 if anybody wants to have a look.

    The reason why I want this PSU is because it is small and that is going to be the most important factor for me when i'm building my HTPC so i can make the case look as small as possible.

    have checked the motherboard user manual, although it does not say anythign about -12v i have found out that i'm going to need a 24 pin connector now lol.

    the only relevant thing i could find was that it said 'if you intend to use a 20 pin and a 4 pin power plug, ensure that the 20 pin power plug can provide atleast 15a on +12v'

    and i dont know if that means the 20pin atx connector and 4pin 12v p4 connector to power the cpu or if it means 20+4 pin atx connector alone.
    what do you think?

    and it does seem that they have taken the -5v pin out.

    so that leaves me with:

    0x -12v ------> x1 needed
    1x +12v ------> x2 needed
    2x +3.3v ------> x3 needed
    4x +5v ------> x5 needed

    i basically need one more of everything!
    and i'm pretty sure that power ON and power OK will need some work doing to it too.

    what do you guys think?
    i should be able to get enough current from each pin as the PSU is powerful enough to feed the computer twice over.

    also the image below shows how to go from PC PSU to xbox motherboard if that is of any help to anyone, maybe we could do the direct opposite?:

    [​IMG]
    The thread goes on to say that R3 should be ommitted and R4 should be changed from 4.7kOhm to 1kOhm.

    Cheers,
    Mubs
     
    Last edited: May 6, 2010
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,271
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    Jan 21, 2010
    I think I'd look for a small form factor ATX power supply. If it were my motherboard I would certainly feel far better using that.

    This is especially true now that I can see that some logic signals need to be inverted, and (the bigger issue) that the standby power is 3.3V from the XBox PSU and 5V from the ATX power supply.

    Here is an example. I googled for "small form factor ATX power supply"
     
  6. Mubs

    Mubs

    8
    0
    May 6, 2010
    unfortunately, they are still too big for my liking pal.
    and the diagrams i posted are for the older version xbox psu's
    the latest v1.6 xbox psu has got 5v standby signal.

    what do you mean by logic signals?
     
  7. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    Sorry to be so blunt, then you are being really stupid about it. If the power supply can not provide enough power, the board is either going to fail to power up or it will crash unexpected and be generally unreliable. I do not know what you are planning to use this board for, but I doubt "it crashes randomly" is going to be an acceptable situation.
    Those two do not add up.15A at 12V is 180W. If the board has a peak consumption of 45W, it does not need 180W. Someone does not know what they are talking about, which means you need to be extra careful about what information you trust.
    That schematic has issues. The 78L33 does not have proper capacitance and will not work reliably. If the person designing that interface made that rookie mistake, what else did he screw up?

    If the X-Box is producing 3.3V and the ATX needs 5V, you need a step-up converter, which is beyond your scope. That is what it will take to "reverse" just that one circuit. I am sure some of the other circuits will have their own issues as well.

    I would reiterate what I said earlier and what Steve has said a couple of times as well: Buy the right power supply.

    ---55p
     
  8. Mubs

    Mubs

    8
    0
    May 6, 2010
    i wont need to step up anything mate as the latest 1.6 psu comes with 5v standby signal.

    and i dont see how the psu will be insufficient for my pc thereby causing crashes and failed boot-ups.
    the PSU is rated at 100w, and the reviewed power consumption of my pc will be 35 - 45w (under load)!!!

    the faulty 180w information you are referring to came from the asus user manual btw

    the xbox PSU also comes with a molex connector (that i wont need)
    so i can take the 5v and 12v pin from there, fulfilling the 5v deficit.
    the only problem now will be powering the cpu with the p4 12v power connector.

    so my net shortage of power supply will now look like this:


    0x -12v ------> x1 needed
    2x +3.3v ------> x3 needed
    2x +12v ------> x4 needed
     
    Last edited: May 6, 2010
  9. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    If you want people to volunteer their time to help you, the least you can do is start by providing proper relevant information.

    ---55p
     
  10. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    Your net shortage is a severe shortage of understanding. It is not a problem of the number of wires. It is about available power/current, available voltages with suitable characteristics (switched, always on, etc..) and the type and function of the logic signals.

    ---55p
     
  11. Mubs

    Mubs

    8
    0
    May 6, 2010
    sorry about the misinformation, i overlooked the fact that the diagrams displayed 3.3v standby.

    If your talking about available power then i do believe that i have enough as my PSU is rated at 100w and my pc wont even touch 50!
    so in theory i should be able to split every single rail into 2 rails and still have sufficient current flowing through it right?

    If i am right then that would mean that the only remaining issue would be the -12v rail and these logic signal (what are logic signals btw?)

    Thanks again,
    Mubs
     
  12. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    How do you know that? Earlier you posted about needing 15A at 12V which translates to 150W just on 12V.

    Second, a 100W power supply does mean you can get 100W on any output. It may mean the 12V is good for 50W, the 5V good for 30W and the 3.3V is good for 20W (those are completely made up numbers, see the power supply spec for the real limits). You also have to make sure that the power supply's output and the board's consumption line for every power rail (every voltage) and the power supply can provide more than the maximum power needed at each output voltage.

    A PC power supply is not a trivial thing and it is not something that you can just willy nilly substitute and hope to get good results.

    An X-box power supply is something that has been designed specifically for the x-box and in order to keep the price down likely does not have any excess capacity on any rail. Unless you are really lucky and the stars line up just right for you, things are not going to match and you will end up with an unreliable system.

    After explaining that for the second time, I am done with this thread.

    ---55p
     
    Last edited: May 6, 2010
  13. Mubs

    Mubs

    8
    0
    May 6, 2010
    Alrighty,
    Thanks for the input buddy.
    not trying to be bitchy, but the 12v 15a story was posted in the user manual and i only call that the first time you explained it that way.

    I'm gonna try and find out how many watts are available on each rail.
    it will more than likely mean the multimeter will need to come out though as i cant see microsoft posting that sort of information online lol.

    do i just measure the voltage and current at each pin and multiply together to get wattage?

    I know everybody is recommending that i just buy a regular atx PSU and believe me i want to, but i do need this pc to be queit small not mentioning the amount of noise that psu's deliver thank to the loud fans.

    could anybody else recommend an alternative way that i can power my pc?
    there is the picopsu but that costs £30 and you still need to go out and buy a 12v dc power brick to plug into the picopsu.... not a cheap option to say the least.

    Would there be a simple way to make one?
    heres what they look like:
    http://www.kustompcs.co.uk/acatalog/info_1667.html

    i also have a 19v - 120w laptop charger and i can get a hold of xbox360 power bricks with wattages of 150-200 if anything can be done with them.

    Thanks for all of the help thus far,
    Regards,
    Mubs
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,271
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    Jan 21, 2010
    If it's not printed on the power supply, the best you can do is measure the output current when it's attached to the XBox. And that's not a trivial task either.

    No, that won't work. As soon as you stick your meter in series with any lead that is duplicated (e.g. one of the many 5V rails) the amount of current going through that lead will fall significantly because of the resistance of the meter's shunt causes most of the power to be diverted to the other leads.

    I'd recommend you head off over to one of the many forums that deal with computer mods.

    There are people who put motherboards and power supplies into everything, and someone may be able to either suggest a small, quiet, cheap (pick any 2) power supply that is suitable, or may be able to supply you with technical information about the XBox power supply.
     
  15. Mubs

    Mubs

    8
    0
    May 6, 2010
    right buddy,
    thanks for the advice,
    i'm a member on a computer hardware forum and nobody seems to be able to give in depth knowledge with regards to current on the xbox psu.

    anyway i have reviewed the plan and i think i am going to go the mini-itx picopsu route:
    http://www.kustompcs.co.uk/acatalog/info_1667.html

    it needs a DC 12v input so am planning on ripping a 150w xbox 360 psu open and just ripping the GND and 12v rail out.
    apparantly the 12v rail has 12.1A so that should be more than enough.

    what i am interested in is that the psu comes with a 5v standby and power enable pins and i've heard that they somehow switch the PSU off when the xbox is switched off.

    would the picopsu have this sort of a mechanism within it to switch the PSU off? although i dont see how, as it only has an uncomplicated 12v and 0v input.

    would this mean that the picopsu would continuously draw electricity from the PSU even after the PC is switched off?

    Thanks again,
    Mubs
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,271
    2,718
    Jan 21, 2010
    The 5V standby normally powers parts of the motherboard that remain on while the computer is "off".

    These include circuitry designed to start the computer when you wiggle the mouse or tap on the keyboard, or when a certain packet arrives on the ethernet port.

    Power enable is different. It is essentially a method to tell the power supply to turn on (and off) without having to deal with dangerous voltages or currents. This may be connected to a low voltage switch on the computer, but more often is controlled by that part of the motherboard which remains powered by the standby supply.

    if the computer does not have a facility to control the PSU, then you will need to manually switch the PSU off and on. The computer may simply reboot when you ask it to turn off as the power won't be turned off after it shuts down.
     
  17. Mubs

    Mubs

    8
    0
    May 6, 2010
    no doubt the computer will have the ability to control the PSU as it has 5v standby and power enable signals on the atx connector.

    my question is, will the picopsu be able to tell the PSU to switch off to conserve energy or will electricity conitnuously be running through to the picoPSU?

    Im thinking not, as the PSU only provides a 12v pin but is it true that when the power brick isn't powering anything it switched off? thats what i have read but my laptop charger seems to remain hot even when it isn't connected.

    Cheers.
     
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If there's only a 12V rail then it will continue to draw whatever power it required to operate in such conditions.
     
  19. samy555

    samy555

    63
    0
    May 11, 2010
    yes
    thank you
     
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