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B&W G3 to ATX Case Conversion
By Timothy A. Seufert
Published: 6/19/2000
(revised 6/22/2000)

    Disclaimer: This page is for entertainment only and is not guaranteed accurate. Performing modifications or other work inside your Mac will void any Apple warranty, may cause damage to your computer or result in personal injury. You assume all risk from the use of any of the information in this article.

B&W G3 ATX Conversion

Refer to the previous Beige G3 article if anything isn't clear.  Although it doesn't have pictures, I went into more detail on some of the procedures I used for mounting a foreign board in an ATX case.

ATX Case Selection

This time around I used the Antec SX1030.  Like the case I used for the beige G3 conversion, it doesn't have a slide-out motherboard tray.  However, the price and features were too good for me to pass up.  The SX1030 cost me about $130 or so from Sparco (including shipping, which was fairly expensive).  That's not cheap, but it has four open 5.25" bays, six internal 3.5" bays with two openings on the front, a 300W ATX power supply with a variable speed cooling fan, and two case cooling fans included.  It also has a bunch of really slick tool-less features like a lot of modern ATX cases do.  For example, you don't have to remove any screws to open the case up to work on things, as the side panel door comes off just by pulling open a latch and rotating it away.  Case fans are mounted in plastic brackets which snap in with no tools.  It also has a very cool mounting system for 3.5" drives.  The only things which turned out to be bad or not to my taste were the speaker and the 5.25" drive mounting system (they use drive rails).

Board Mounting

Mounting is the same process as a beige G3: line the board up in the chassis with some PCI cards installed and screwed in, mark where mounting holes are going to go with a scratch awl, drill holes, and tap them.

Here I'm tapping one of the holes I drilled to mount the motherboard.  The motherboard standoffs that come with Antec cases use #6-32 UNC threads.


Oops!  I messed up the alignment of a couple holes.  When I tried mount the motherboard, two holes were too far off center to use.  I didn't want to leave the board unsupported at those spots (they were close to the PCI and memory slots, where you need some support under the motherboard for plugging in cards), so I bought a bag of assorted motherboard mounting hardware at a PC store and selected a type of nylon standoff which butts up against the motherboard tray.


Here's a picture of the board in place, with a PCI card in one of the slots to make sure it's aligned right.  The small board to the right of the motherboard is the B&W G3 front panel board, removed from the original sheet metal housing (more on the front panel board below).  The second picture shows the other part of my solution to the problem of misaligned holes: I used a cable tie looped through a couple extra holes I drilled in the case to hold the motherboard down, instead of a screw.  I only had to do this for the misaligned mounting hole near the PCI slots, the other one wasn't as critical.  Fortunately for me, Apple put an extra hole in that corner of the board which I could use to loop the cable tie through.


I/O Cover Plate

Needless to say, the standard I/O covers for ATX motherboards won't match the B&W G3's port layout.  Not even close.  So I set out to make my own.  After mounting the motherboard, I noticed that there was about 1/8" of clearance between the edge of the board and the plane of the ATX I/O port opening.  I happened to have some 1/8" aluminum plate around, so I hacksawed out a piece of it.  I then drilled, sawed, and filed out holes in the plate to roughly match the G3's ports.

Normal ATX I/O port covers are made of thin sheet metal and press fit into the opening.  Instead of doing that, I made my plate larger than the opening and screwed it in.  I drilled and tapped holes for #4-40 UNC threads all along the top of the plate, and then drilled matching holes on the case for the screws to pass through.

Note that I also provided a hole for the screw which secures the FireWire pod to the back panel, needed for good mechanical support to take the stress from plugging and unplugging FireWire cables.


ATX Power

The B&W G3 uses a power supply that's almost but not quite identical to an ATX supply.  The lone difference is that the wire which supplies -5V on an ATX supply (pin 18) becomes a ground wire in the B&W G3.  If you just plug in an ATX supply without any modifications, you'll short out its -5V output.

One way of dealing with this is to simply remove the original ATX supply from the PC case and substitute the supply from the B&W G3.  However, this means that you can't take advantage of the 300W or bigger ATX supplies, one of the reasons to do an ATX conversion in the first place.

The other solution is to snip or remove the -5V wire from the ATX connector.  Actually, I found an ATX power extender cable at a PC store, and snipped the -5V wire on that instead, to avoid permanently altering the power supply's own wiring.  You'll likely need an extender cable anyway. (I had a link here to a 12in long PCpower & cooling extension cable but they no longer list it. Check local stores or the web/ebay for these, they're very cheap.-Mike)
The G3 motherboard's power connector is all the way at the bottom of the case, and few PC ATX supplies have a power cable long enough to reach.  Here are pictures of the female and male ends of the extender with the -5V wire snipped out.

The -5V wire on an ATX supply is normally the only white wire in the cable, but don't count on it.  I downloaded the ATX spec the other day, and it was pretty careful to note that the color scheme was only a recommendation, not a requirement.  Make sure you snip the wire using the photo on the left as a reference.

Here's a picture of the modified extender cable installed in the system.


Front Panel (Power/sleep LED, reset & power & interrupt switches)

The B&W G3 uses a front panel board for all of these functions.  It connects to the motherboard via a 20-pin ribbon cable which plugs in near the PCI slots.

The B&W's front panel board also acts as a power supply.  It accepts power from the main power supply via a drive power connector.  It has a step-up regulator which generates 24V DC from the drive power.  The 24V power is then routed to the motherboard via a 3-wire cable which plugs into a connector near the DIMM slots.

You may not actually need the front panel board's power supply.  I tried booting the machine with the 24V power disconnected from the motherboard, and it seemed to work fine.  I suspect that it is only there to supply the FireWire bus.  FireWire specifies that the power available on a 6-pin FW connector can be anywhere between 8 and 30 volts, unregulated, at a fairly high current.  If my theory is right, the only thing you'll lose by not having this in the system is the ability to run bus powered FireWire devices like VST's 2.5" FireWire hard drives.  [See Portable Firewire HD article for info/tests on these drives.-Mike] If you don't need this, you can probably get away without mounting the front panel board in the case at all.

For the remaining front panel board functions, you can do one of three things:

  • Mount the original front panel board and solder wires to the switches and LED on that board.  Blech.  Ugly.  But it would work.
  • Extract the socket pins from the plastic housings on the original PC front panel connectors and plug them in to the appropriate pins on the B&W G3 motherboard's header (see below for pinout).  You probably won't be able to get the power LED to function right this way; not only is Apple's power LED 2-color but the front panel board also contains a LED driver circuit.
  • Do what I did and breadboard a replacement for Apple's LED driver circuit, with a SIP header to plug all the LED and switch connections into.



    This is the breadboard installed with everything plugged in.  I made the short length of ribbon cable using parts obtained at a local electronics store, but if you don't have access to this kind of stuff just use the original and find a place to stuff all the excess cable.  The wires at the top of the board go to a drive power connector, which supplies +5V to run the power/sleep LED.  Visible at the bottom are all the front panel connections going off to the LED, switches, etc.  The chip is a 7402 quad NOR gate used to decode the LED control signals from the motherboard and drive either the power (green) or sleep (amber) circuit of a 3-color LED.  Even places like Radio Shack probably carry 74-series parts, including the 7402.

    (Also visible in this picture is the CD/DVD audio cable.)


    Here's a schematic for the LED driver circuit and the connections between the motherboard and the various switches.  For the tech-heads out there, I show the 74HC02 (CMOS version of the 7402) mainly because that's what Apple used.  Most HC logic families can source enough current to drive a LED, so it should work fine.

    I forgot to put resistor values in this schematic, but probably anything from 50 to 150 ohms will work fine.  If the LED seems too dim, substitute a lower resistor value.

    Here are some illustrations of the pinout of the motherboard's front panel connector and the pinout of the 7402 DIP IC.  Note the locations of the notch in the motherboard connector's housing and the notch in the IC package.

    If you don't want to construct an interface board, connect the ATX power-on switch to pins 5 & 10 (highlighted in green) and the ATX reset switch to pins 3 & 8 (highlighted in blue).  You'll have to live without the power LED.

    Apple's pinout doesn't lend itself to just plugging the normal ATX switch connector into a couple of the pins.  You'll have to extract the socket-type pins from the plastic housing of the ATX switch cable and put them on the motherboard connector individually.

    This is an illustration of a typical ATX power/reset switch connector.  To extract the pins, you'll need to disengage the plastic locking tabs, which are an integral part of the molded connector housing.  Just use something thin and pointy to lever each tab up; the tip of an X-Acto knife works well.  While the tab is levered up, the corresponding socket pin can easily be pulled out of the housing.  Once they're out, it's a good idea to shrink a piece of heatshrink tubing around each socket pin and the first half inch of wire, for strain relief and protection from shorts.  Then just push the socket pins onto the appropriate pins in the G3 motherboard connector.

    I also made some modifications to the ATX case front panel.  I drilled a hole to mount a multicolor LED for the power/sleep LED and another hole to mount a momentary-connect pushbutton switch for the NMI (programmer's) switch.


    Processor Cooling Fan

    The case I'm using has plenty of cooling, but of course doesn't guarantee some airflow over the processor the way that Apple's case designs do.  I installed a fan on the factory G3 heatsink to make sure there would be enough cooling for the CPU.  Nothing fancy, just a low profile fan bolted right on.  The screws I used are #8-32 UNC, which turns out to be just large enough to engage the tines of the G3 heatsink.  I did have to drill out the fan's mounting holes for these screws to fit.

    Also visible in this picture is the speaker connection.



    The only cheesy thing which came with the Antec SX1030 was the speaker.  I've come to expect little out of the speakers installed in PC cases, but this went a little too far: instead of a real speaker, they used one of those little piezoelectric buzzers.  What's more, either mine was bad or it blew out in the first instant it was driven by the G3 motherboard, because it made nothing louder than an extremely faint buzz.

    I fixed this by finding a real speaker thin enough to mount between the case's metal shell and the plastic front piece.

    The finished product!

    Add a few drives and RAM, and we're cooking with heat.

    The paper taped to the bottom is a schematic of the LED driver circuit and key to the front panel connections, just in case I ever need it again.

    Visible in this picture are the reasons I bought this case: the very cool 3.5" drive carriers.  The carriers hold 3 drives apiece and can be removed with no tools.  They're easier to work with than the drive sleds in the original B&W G3 case.  You can also mount an 80mm fan at the front of one of the two carriers to cool the drives inside.

     -Timothy A. Seufert

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