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Converting a Beige G3 Desktop to an ATX Tower
By Trevor Morris
Published: 1/15/2003
Beige DT in ATX Case

The obvious question one might ask is why would you want to move a Macintosh system into a PC case? The reason is simple. Although some find contemporary Macintosh cases cute, it just so happens I am not one of them. Furthermore, the G3 (Desktop model) only has a single 5 1/4" drive bay, which is populated with your CD-ROM drive. And while it has three 3 1/2" drive bays, which can house a zip drive or additional hard drives, if you want to add additional optical drives you are out of luck. (The Beige G3 Minitower case has three 5-1/4" bays.-Mike)

My principal motivation to give this a shot was the rat's nest of SCSI cables that I had behind the computer desk my G3 called home. The external SCSI Zip Drive, external CD-RW drive and monster Microtek scanners had an unbelievable mess of power and scsi cables. While I don't believe it is possible to mount a scanner internally, it was possible to take the CD-RW out of it's SCSI enclosure and trade my external SCSI zip drive for an internal SCSI drive, thus eliminating all the external SCSI cables with the exception of the scanner.

This is the configuration of the system, one of many beige G3's I own.

  • 300MHz IBM PowerPC 750 overclocked to 333mhz,
  • 256MB of SDRAM
  • 40GB Samsung Hard Drive
  • 52x LG CD-ROM Drive
  • 6x/24x Teac SCSI CD-RW Drive
  • Zip-100 Iomega SCSI Drive
  • 16MB 3Dfx Voodoo 3 Videocard
  • Opti Firelink USB Card

When it was introduced in 1997, the beige G3's were very impressive machines that ate their Pentium contemporaries for lunch and heralded what was perceived as a Macintosh renaissance.

The motherboard of the beige G3 is known as "Gossamer". It was originally intended to be the basis of inexpensive white-box Macintosh clones. Based on the Motorola MPC106 SDRAM chipset (XPC/MPC-106 Memory/PCI controller-Mike), it would have used ZIF PowerPC 603e or G3 processors. However, as everyone knows, when Steve Jobs returned to Apple, his first victims were the Macintosh clones.

At the time, the next generation Apple logic board was known as "PEX" or "Power Express" or the Power Macintosh 9700. (see As it would turn out, what was supposed to be a low end clone board, was, in fact, a great deal faster than PEX by the virtue of its SDRAM support and faster bus speeds. It was cancelled and Apple went ahead using the "Gossamer" logic board as the basis of the original G3 line.

The Beige G3 desktop is based on the Power Macintosh 7500 chassis, which is a nice desktop case but lacks the expandability found in a tower case. This particular machine has a pretty seriously damaged case, the result of a close encounter with a 21" monitor, making it a prime candidate for the transplant.

When you move a beige G3 from its original home and into a more spacious case, there are a number of issues that have to be confronted. For this project I used the Lian-Li PC-10 Aluminum case.

Lian Li case

Part One: ATX Identity Crisis
The beige G3 is, from an electrical perspective, an ATX system, as the result of it originally being designed to be a white box board. Its DNA is visible via the solder pads for a PC floppy drive and solder pads for inline L2 cache. It does however hold onto some proprietary traits.

1. Integrated Video and IO Shield: This is probably the second most annoying issue to come up, and the solution can put you in a position in which you can inflict unknown terror on your logic board. The problem is that the video port extends past the IO shield in an ATX case. You either have to wreck the new ATX case or replace the video card. Another issue is that because the logic board doesn't have the conventional PS/2 IO ports there is no generic IO shield that will fit back there, You will have to come up with your own. Again, the solutions to these issues will be addressed later.

2. The "Personality Card": The final and by far most inflammatory issue when it comes to moving the beige G3 into an ATX case is the soundcard. Again, up until this point, any solution involving the use of the original Personality card involved dismembering your new case, or purchasing a 3rd party soundcard. This was a less than attractive alternative in most situations due to the fact that unlike Windows PC's, you can't just wander down to CompUSA and pick up a cheap $19.99 soundcard. You have to choose between expensive professional cards or the Creative Labs SoundBlaster Live! for which Macintosh support was at best an after thought. And, it wastes one of your valuable PCI slots. Again, this like all else, will be discussed later.

Let's Get Started:
First of all, let's address the parts you will require for this project.

  • Beige Power Macintosh G3 with Audio Out Personality Card
  • PC Audio Riser Card
  • PCI Videocard or DB-15 Ribbon Cable (Midi\Joystick)
  • ATX Case and Power Supply (Lian-Li case STRONGLY recommended)
  • Pentium HSF with removable clip
  • Soldering Iron and solder
  • Electricians Tape

The Video Issue:


Note the removed DB-15 Port (onboard graphics output connector) and the screw in the left hole once occupied by the DB-15 fastener.

Right off the bat, you are going to have to remove the DB-15 video port on the logic board. This is really unavoidable. To do this, flip the board over and de-solder the fasteners. Holding the DB-15 port to the logic board, twist the fasteners with the soldering iron. Once the bulk of the solder has been removed, using something like a credit card or spatula, push upwards on the DB-15 port and flex it back and forth until the pins break. There aren't any traces under the DB-15 connector you have to worry about damaging. It is important that you leave the holes where the fasteners for the DB-15 port were clear because you will need to put a screw in one of them when you mount the logic board in the new case.

Now, obviously, once the integrated video port has been disabled, you have to find another means to hook up a monitor to the systems. There are three ways to go about doing this. The first possibility is to simply buy a replacement video card such as an ATI Radeon 7000 or other video card. Another possibility is to use a PC Rage II or Rage Pro (depending on motherboard revision) in place of the onboard video. Because you are only removing the physical DB-15 port and the original graphics card remains soldered in place, if jumpered correctly the PCI Rage II or Rage Pro will ignore it's own firmware and instead use the firmware of the Rage II or Rage Pro built into the motherboard.
(Note: In 1997 when I originally started the G3-ZONE site section there was one report of a PC RagePro card that had a jumper on it for use as a 2nd graphics card in PCs I believe, and was reported to work in a Beige G3. This is not true of later models (Mac graphics cards require mac firmware on the card). You're probably as likely to find a Mac RageII/RagePro card as a PC one now, but regardless, I wouldn't waste a PCI slot a card that old, which isn't even supported by the Apple DVD players.-Mike)

And there is a third option that allows you to continue using the integrated graphics although you have removed the DB-15 port. However, this process is quite difficult and can be complicated by different wire orders encountered in DB-15 ribbon cables. Take a DB-15 port attached to a backplate. You can find this part in virtually any old PC without a built in soundcard. Strip the wires, and carefully observing wire order, solder them back in place where the removed DB-15 port was. Personally, I don't think this is worth the effort given that you can get a Voodoo 3 for under $20 these days.,.

At the moment, I am using a Voodoo 3 2000. I hope to replace that with a Rage 128 or Radeon at some point. (A Rage128 or Radeon card is required for DVD Player support, plus they have OS X drivers.)

The Sound Issue:

AV card

To start off with, you will have to remove the jacks for the speaker and microphone. It is easiest to use needle nosed pliers and literally peel off the tin cover. Once you have done that, the only thing holding the jack in place is the solder pads for the contacts. At this point, you can take your pliers again and shear off the jack. After you rip off the jack, all that will remain are four contacts sticking out. The first contact is ground, the second is left the third is right, the 4th contact doesn't appear to do anything. (see illustration)

Now, take your sacrificial audio riser card and solder three wires that should be about 4 inches long to each of the three lines on the jacks of the riser card. Then, solder those wires to the corresponding pads on the riser card. Unfortunately, this might require a certain degree of trial and error. However, from my experimenting, in which I tried at least 25 different possibilities, I don't think I damaged anything.

I haven't really figured out a means by which you can mount the physical personality card. However, just planted in the personality slot, it would appear to be reasonably solid, although it is certainly something to keep in mind.

The ATX Identity Crisis:

MB installed

If you mount the logic board into the standard cups in the ATX case, your board will be about an eighth of an inch too far forward to correctly install any PCI peripherals. The solution to this issue is really pretty straight forward, although it requires a certain degree of care, (assuming that you are among those who don't want holes in the side of their case.) The most simple means by which this can be addressed is to install a pair of PCI cards and place the board flush with the rear of the case. Mark the holes in the board accordingly. Using a drill, telepathy, laser cannon or whatever instrument you like, drill holes in the motherboard tray.

There is, however, a much better solution, Lian-Li cases. While very expensive and strictly utilitarian, they are the best cases on the market. (I prefer the CoolerMaster Aluminum Cases personally, but both are good.-Mike) The PC-10 case costs about $110US ($160CND\$190SG\ 105EU\f70UK) and accommodate just about any motherboard conceivable. Including Macintosh motherboards.

Another ATX issue presented by this semi-proprietary logic board is that you need to fabricate your own I/O shield. The board in question's ports will not line up with a standard ATX I/O shield. This was an incredibly frustrating situation because without an I/O shield, the inside of the computer will quickly be overcome by dust and grime. In addition, without an I/O shield, the slightest tug on any of the ports can result in them literally being ripped off the surface of the board.

There are a number of possibilities. However, assuming that you don't have access to a metal punch or anything else of the like, the easiest solution I have found is to use a material called cardboard.

To make an I/O shield, you will need to remove the EMF (EMI/RFI) shielding in the original G3 case from along the bottom of the logic board and trace the outline of the port openings (with the exception of the removed video-port). You should line up the openings for the serial ports along the extreme right edge of the sheet and cut away. Seal the edges with electricians tape and you're done.

IO Shield

The Lian-Li case uses tin clips to mount the motherboard instead of a combination of brass cup screws and nylon stand-offs. For best fit, mount the clips in the following holes. (see illustration)

The last thing you have to do is switch the power supply jumper to PS/2. This jumper is above the PCI slot on the left hand side of the board and is labeled (PS/2 Supply Mac Supply). Obviously, PS/2 selects the ATX power supply. (Note: The minitower Beige G3 models are usually already set to PS/2 for an ATX supply. See prev. Beige G3/ATX case conversion article from 2000.-Mike)

MB tray Mtg Holes

When it comes to choosing an ATX power supply for this endeavor, any power supply on the market will be more than adequate. The original power supply is only 150w. That might be adequate for the stock configuration, but in this case, the reason you are probably doing this is for increased expandability and when you load up your system with multiple hard disks, CD-ROM drives and the like, you will soon require some pretty serious wattage. There are several major brands of ATX power supplies. These are more expensive and generally quieter than those less expensive generic power supplies. However, we are at a point now that junk power supplies aren't really made anymore. Any ATX power supply 250w or better will do the job. I am using a 300w ATNG. A basic 300w power supply will cost about $20. A name brand, such as Enermax or Powerman, will cost anywhere from $40 to $100. It really should be reasonably obvious as to how to hook up the power supply. Now, really all that leaves you is the painfully obvious process of physically installing your peripherals, cards and drives into your Macs new home sweet home. You're done!

Previous ATX Conversion Articles:

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