How to use ATX power supply in Gigabit/Digital Audio

Discussion in 'Mac Pro' started by spinne1, Dec 18, 2006.

  1. spinne1 macrumors 6502a


    Mar 12, 2005
    Hermitage, TN USA (near Nashville)
    Step by step instructions for using an ATX 24-pin power supply in a Gigabit Ethernet/Digital Audio Powermac G4 (one way to do it anyway):

    First, know that to boot the G4s up, you MUST have at least +12V of power going to the G4's pin #22 spot (white wire) even with the computer turned off. This is called standby power (I didn't know what it meant until a few days ago). ATX power supplies generally only have a +5V SB power source which is not enough. You must use some method of getting the +12V to +28V standby power to the G4's pin #22. I will outline the method I used but there are others (ideally get a ATX power supply with +12V standby, but they are not so easy to find). I am typing this on my G4/533 with an Antec SP-500 power supply. Why do this? With an ATI Radeon 9800 256mb graphics card, three hard drives, a DVD drive, a SCSI card, a USB 2.0 card, a USB 2.0 hub with four devices attached, and a newly aquired G4/1.4 Ghz card (which meant two additional fans for cooling control), I figured the original power supply was overextended. So, here's how it can be done:

    1. Make sure the ATX power supply you want to use fits your case and has the power cord hookup in the correct position (lower left corner).
    2. Make sure the ATX power supply has a long enough motherboard harness, or else you will need to buy an extension (which you may want to do anyway to avoid mutilating the original power supply's wiring harness).
    3. About three inches from the motherboard harness connector (same with all future cuts), cut the ATX wire #8 (gray). Tape the end of the gray wire going to the power supply. You don't use it for anything.
    4. Cut wire #12 (orange).
    5. Remove 1/2 inch of wire insulation from the stub of gray wire coming from pin 8 in the harness connector and from the long orange wire (that used to go to pin 12) that goes to the power supply and solder them together. Cover with heat shrink tubing (which you must put on before you solder) or electrical tape.
    6. Cut wire #9 (purple). After cutting, strip away 1/2 inch of wire insulation from the end going to the power supply. Ignore for now. The other stub end can be left where it is. It is sitting in a "no wire" spot on the motherboard harness of the G4.
    7. Cut wire #11 (yellow) and seal the end of the wire going to the power supply with tape. You will not need this wire unless you want to power your graphics card with it or something (generally not necessary).
    8. Strip away the insulation but don't cut through the wire of wire #7 (black) about three inches from the motherboard harness. Use a sharp pocketknife or similar tool.
    9. Strip away 1/2 inch of insulation from the stub of wire #11 (yellow) that goes to the motherboard harness and solder it to the opening on wire #7 (black).
    10. Burn the plastic with the tip of your soldering iron around pin 24 ONLY (don't burn any of the plastic around pin 23) and keep wiping off your soldering tip with a thick paper towel wad until you can remove the pin completely. Then scrape off the remaining brittle plastic from the pin using a pocketknife or exacto knife.
    11. Insert the newly removed pin and attached black wire into pin hole #20 (which becomes pin #19 on the G4's motherboard).
    12. Cut wire #23 (red). Tape the end going to the power supply. You don't use that end. Remove 1/2 inch of insulation from the stub end. This wire will be the location of your 12V-28V standby power.

    Here is where you must decide your method of powering the standby power. I chose to use the front panel board from a Blue and White G3. I had an extra one for parts lying around. The parts you need can be had pretty cheap if you can find a junk B & W G3, or if you look on ebay. (heck even working ones are super cheap now)

    13. The next bit of directions are assuming you will use the front panel board from the G3 (the board that sits directly behind the power button on the front of the computer.) It is in a metal cage. Leave it in the cage but remove it from the computer. Remove all wires from it in order to remove it.
    14. You will need about eight inches of the smaller three prong wire that was attached to this board. Remove it at the motherboard end and chop it off about eight inches from the harness. There are small white, yellow, and red wires along with a ground wire inside the gray insulation of the three prong wire. Pull back the ground wire about an inch and tape it to the gray insulation.
    15. Tape back the yellow wire over the previous tape job of step 14.
    16. Strip about 3/4 inch of insulation from the white wire.
    17. Obtain an extra molex power connector with about six inches of wire attached to it (the molex is the standard four-prong power connector that goes into all PATA/IDE hard drives, etc) OR use the end of one of the ATX power supply's power lines to attach to the B & W G3's front panel board. If you use the ATX's line, you must cut the yellow and red wires about five inches from the end connector and strip 1/2 inch of insulation from each on the wires going to the molex connector. The other end of the wires tape off. You won't use them.
    18. If using the ATX's molex connector, solder the newly cut yellow and red wires along with the white wire from step 16 (from the small three prong harness) to the purple wire from step 6 (it is the only purple wire). Use the purple end going to the power supply (the other end is dead, remember?). This 5V standby power will go to the small white wire to activate the front panel board's DC transformer, while the 5V going to the red and yellow wires will allow the board to jump up your voltage from 5V to 14V. Normally the front panel board would jump your power up to 24V. However, that is if the red wire coming in has 5V and the yellow wire coming in has 12V. In this case we don't have 12V of standby power to give the front panel board to allow it to jump it up to 24V. If we did have 12V of standby power we could simply hook it up to pin 23 on the ATX's motherboard connector and not use the front panel board at all. That 14V is enough to power up your Mac using the front power button and I am told also enough to power your firewire (but NOT your ADC).
    19. Solder the small red wire from the gray insulated three wire group from the front panel board to pin #23's red wire stub that you cut in step 12. This little red wire is the source of your 14V standby power that allows your G4 to boot up.
    20. Set the front panel board down on the bottom of your case towards the front of the computer cage side up. I just leave mine loose. As long as you don't move the computer forcefully you will be fine.
    21. Hook the motherboard harness to the G4's motherboard. Leave the ATX pin #12 (was orange--but now is an orange stub) hanging out off the end of the motherboard connector towards the front of the computer.
    22. Double and triple check your wiring to make sure there are no open ended wires and that all wires are sealed and that your connections are correct (use the diagram to help).
    23. Test the startup by pushing the front power button on your G4. Does it light up and the computer fire up? Good! You are in business!

    It is always possible I made a mistake and mistyped or forgot something. Please correct me if I am wrong in any way. The only step I am not nearly 100% certain on is the one with the three-prong gray insulated wire set from the front panel board. I believe it was the white wire I used to attach to the purple wire +5V standby power of the ATX power supply in order to activate the front panel board, but it is possible it was the small yellow wire. You can test by simply using a jumper before soldering to see if it works correctly on the white wire first.

    I, of course, make no claim of authority and disclaim all damage you may do to your computer by attempting these steps. Proceed at your own risk.

    Here is a diagram of the above steps:
  2. Smackintush macrumors newbie

    Jan 10, 2007
    ATX Conversion

    I am having powerup problem with my Sawtooth, and am seriously leaning towards the power Supply as being the Culprit. I really don't want to pay a ton of cash for a MAC replacement, and I would also like to ad more drives to the G4, So I am seriously thinking of going th same route that you did.

    I was just wondering if you had any pictures of the changes you did for referance I could use to guide me through the correct steps. Another question I had was you stated that you used the powerup swith from a B&W G3, Did you use just the swith board or the whole Blue front face of the G3?

    Thanks a ton in Advance!
  3. cynerjist macrumors regular

    Nov 8, 2006
  4. spinne1 thread starter macrumors 6502a


    Mar 12, 2005
    Hermitage, TN USA (near Nashville)
    The Sawtooth is a different animal and can more easily accommodate an ATX power supply. You do not need the front panel board from a B & W G3 to use an ATX with a Sawtooth:

    The only reason to use a B & W G3 front panel board is to get the minimum 12V generated in order to boot up a Digital Audio or Gigabit Ethernet Powermac G4. Sawtooth's do not require this to boot.

    Follow the link above and it will not be too hard. Just make sure the power plug is in the same position as on your power supply.

    Lastly, no I didn't take any pictures, but in your case it really will be VERY easy. Get a soldering gun and a pocketknife. Follow the directions in the link above which should take you maybe 30 minutes total. Then install! (keep in mind that the side support screws on the Sawtooth's power supply will likely not work with the new ATX power supply as there will be hole there. You could drill one, or simply use the four screws on the back of the power supply and call it good enough.)
  5. Smackintush macrumors newbie

    Jan 10, 2007
    My Fault

    I stated that I have a Sawtooth, but after further research, I found out that I actually have a Gigabit Ethernet G4, My apple power supply actually has a 22 pin connector on it and not a 20 pin.

    My only other question is that this is the power supply I am looking at using, Is this the exact same one that you used, or is it an updated version of the same one.

    I plan on doing the mods this weekend I'll let you know how it all worked out.
  6. Lord Blackadder macrumors G5

    Lord Blackadder

    May 7, 2004
    Sod off
    Very cool, thanks for posting this!

    My Digital Audio has done very well so far with the stock PSU, but if it went south, I'd try the ATX swap.
  7. spinne1 thread starter macrumors 6502a


    Mar 12, 2005
    Hermitage, TN USA (near Nashville)
    Yes, this is the same power supply I have. Keep in mind that there will be a lot of cordage running around and you'll need zip ties or some way to control the chaos (otherwise shutting the case gets difficult).
  8. Smackintush macrumors newbie

    Jan 10, 2007
    You Rock!!

    Thanks for all the advise and guidance.
  9. at77 macrumors newbie

    Mar 31, 2008
    don't forget the ground wires

    hey there,
    just adding that if you use a separate molex connector, you must also connect the two black wires to ground. otherwise you end up with under 5v coming through instead of 14v.
    thanks for the posting.
  10. hunter3740 macrumors member

    Aug 28, 2008
    Pittsburgh, PA
  11. Earl Urly macrumors regular

    Jul 11, 2004
    If you'd rather have someone else do this stuff, go to:

    This guy is selling adapters for ATX power supplies.. all you do is buy an appropriate ATX supply (the ones he suggests work fine), hook in the adapter, and you're all set.

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