Modding a G4 Tower to an ATX Rackmount Case

DISCLAIMER: Do not try this at home. If you attempt to duplicate this project without a strong knowledge of computing, electronics, or machine tools, you may very well (a) electrocute yourself (b) destroy your tools (c) destroy your computer hardware (d) burn down your house (e) be sued by Apple for violating their EULA (f) turn into a blue penguin and be fired into the sun by an angry mob. I, the author of this article, am not responsible for any of the aforementioned.

Recently, our company upgraded our system for accessing the company database. We purchased an Apple XServe dual G5 to be a mySQL data source for our MS Access front-end. This configuration is worthy of an article on its own, but alas, I don't have the database savvy to explain it properly.

To maximize space, security, and noise-reduction, we invested in a 12U server cabinet called the XRackPro. This allows us to properly mount our XServe as well as our other 19-inch server hardware, which includes a pair of vintage Cobalt RaQ4s and a 16-port ethernet switch.

I was interested in moving another server to Mac OS X Server because of the ease of setting up services and remote management. Unfortunately, XServes are expensive, and we have a limited budget. It's easy to use a vintage Mac tower as a server, but it would be difficult to fit inside the cabinet. Alternatively, if it sits outside the server cabinet and adds to the general office noise, then the fancy server cabinet is going to waste.

So I started to think: what if I could take a motherboard from a Mac tower and mount it in a PC ATX Rackmount case?

A little explanation for my non-technical readers. Almost all server hardware is sized at 19-inches wide and in heights at intervals 1.75 inches high. This so called Rackmount hardware is measured in "U"s, where a 1U server (like the Xserve) is 1.75 inches high, and a 4U server (like the XServe RAID, or a rackmountable ATX case) is 7 inches high. By standardizing sizes, you can have large racks or cabinets which hold lots of servers and equipment of differing types.

Parts

It took me a fair bit of running around to get the components for this project, but I was able to get everything locally. I obtained a G4 400Mhz PowerMac tower from my local new and used Mac dealer (The Mac Market). The ATX rackmount chassis I obtained from a local computer specialty parts store whose name I won't mention here (with a wide selection of parts, you trade customer service for a bunch of disaffected young guys talking about CounterStrike).

After having a look through the ATX case, it turned out to be a lot nicer than I expected a "generic" item to be. There was tons of space for the motherboard, lots of buttons and LED indicators on the front, and a pair of fans mounted on a rail in the middle of the case. My favorite feature was the semi-enclosed space for hard drives cooled by a big fan which drew it's air through a filter at the front of the case. Spiffy!

The G4 is a pretty standard previous generation machine. It's got USB, Firewire, 100 Base-T Ethernet, an AGP graphics slot, SD-RAM, and 3 PCI slots. The system came with an Orange Micro SCSI card in one of the slots, but I just pulled the thing out and set it aside (God knows what we'll do with a SCSI card that isn't Windows compatible). Some dusting was required. I have found that a can of compressed air can be most efficacious.

Transplanting the Motherboard

				Obviously, the first step was to just take the G4 apart completely. This is a task in itself, because the old mac towers use hex screws and everything is fairly well-integrated (I was glad when I was finally able to remove the power supply). With the PSU and motherboard in hand, I dropped them into the case to test-fit things. Luckily, the PSU design is identical to a PC version, so it fit right into the case no problem. The motherboard was a bit more of a challenge. Unfortunately, I found that the clearance at the top of the board (next to the power supply) was quite minimal. If I wanted to line up the PCI and AGP slots appropriately, the speaker port on the motherboard panel would be obscured by part of the case. I pondered whether or not this would be an issue for a while before deciding that my rackmount server didn't need a speaker port.

The biggest challenge for this mod involved the mounting of the motherboard. Because the G4 motherboard has mounting holes in different locations than a PC-ATX board, I would not only have to drill, but also tap screw-holes for the motherboard standoffs. For those of you who don't know, tapping is the process of cutting threads into a hole to accommodate a screw or bolt. I brought one of the standoffs to my dad's favorite machine tools store (KMS Tools). A staff member was very helpful in measuring the thread size (#6-32 UNC) and providing an appropriate drill bit, tap, and some cutting fluid.

		The mounted board with the heat sink removed.

I carefully positioned the motherboard (with an AGP card in place) and marked the holes. The metal tray which holds the motherboard was detachable, so I removed that prior to drilling. I had heard a lot of horror stories about breaking taps, but I found the process remarkably easy myself. I screwed the standoffs into the holes and they fit perfectly. Of course, with my amateurish measuring methodology a few of the holes were off center. Overall though, the motherboard could be securely fastened into the chassis and was well-supported.

Pay no attention to this hole. It's meant to be like that... really....

Naturally, with everything in place, I wanted some immediate assurance that I hadn't somehow destroyed $400 worth of hardware. So I plugged the power supply in, hastily modified the connector for the ATX-style front power-switch connector, and plugged an old iMac speaker into the board. I pressed the power switch, waited, panicked for a few moments, then realized that I was looking at the pinout diagram for the motherboard panel-connector upside-down. I corrected the switch wiring and tried again. The fans all whirred to life and I was greeted with the wonderful sound of the Mac startup chime. "SUCCESS!!!" I shouted.

The machine goes "PING!"

System Configuration

One last but important item remained before I could start using the machine regularly: cooling. The rail to mount the chassis fans on went right above the processor heatsink, so I had to use a little additional hardware to mount the fan. The fan draws air over the processor, and blows it out the rear of the case. It's not ideal, but given the space constraints I felt it was the best option.

With everything in place, I could begin to focus on configuring a useful system. First of all, I wanted to wipe the boot drive clean and install our copy of OS X Server 10.3. This went easily enough. However, once OS X was installed and I began to configure settings, I was beset by frequent and seemingly random freezes. I wouldn't even be greeted by a kernel panic message. I swapped out any new RAM I'd added but the freezes continued. I began to worry that I'd somehow damaged the hardware during the transfer.

Fortunately, after a little research I came to the realization that the freezes were occurring because no one had ever applied any firmware updates to the machine; it was running on the factory default that it had shipped with back in 1999. A firmware update is available from Apple which, as one of it's many listed features, "drastically improves stability under OS X". Despite the obvious market for this fix, for some reason Apple requires that the firmware updater be run under Mac OS 9, which I had deleted from the machine.

Drat.

Unable to find any OS 9 install discs at my home, I decided to simply copy the installation on my PowerBook G4 to the PowerMac. I brought a FireWire cable to work and booted my laptop into Target Disk Mode, which allowed me to connect it to the PowerMac as a FireWire hard disk. I copied the OS 9 installation, booted into OS 9, and applied the update. Since then, system stability has been a non-issue.

For the particular system I needed a second ethernet connection and an extra hard drive. We've got plenty of IDE hard disks to spare around the office now that SATA is slowly taking over. There's also no shortage of ethernet cards. So I was able to find one that was mac-compatible: the D-Link DFE 530TX+.

Finishing Touches

A bit of a sticky step was wiring up the power LED and front panel switches. The PowerMac G4 uses a circuit board behind its front panel which connects to the motherboard. There's some differences between the ATX connectors and the Mac motherboard connectors, but it's possible to make them play nice together. I used a diagram provided online to help me decipher the pinout. Since the Mac motherboard provides 3.3V power for the power indicator, a 50 Ohm resistor was required to connect to the power LED in the case. I won't show you a photo of my ghetto-esque rewiring. The important thing is that it works. ;-)

A spot of luck: the cooling fan for the G4 processor is the exact same voltage, amperage, and size as the ATX case cooling fan. By splicing the old connector onto the new fan, I can power it using the appropriate connector on the G4 PSU.

In this photo you can see how I (mostly) closed off the panel with a piece of plasticard. Also rather ghetto, but since the enclosure will be inside a server cabinet I don't think I'll have much to worry about in terms of dust accumulation. If you look closely you'll see that I also took the time to mount the old Mac serial port in an appropriate spot provided on the back of the case (even thought we'll probably never use it).

Quirks

The system is a low-cost rackmount alternative to Apple's XServe systems. It works well enough for the purposes we'll need it for. When you come down to it though, this is still just a hack, so there are a few things that don't work quite to my liking. They might be possibilities for improvement down the road.

- The IDE chain was extremely difficult to properly configure. The case isn't as tight as the PowerMac G4's original case, and it would take an exceptionally long IDE cable to reach both the DVD-ROM drive and the secondary hard drive. As such, I can't have the DVD drive hooked up to the secondary IDE chain (which has the ATAPI support) at the same time as the secondary hard drive. No matter, since I'm done installing software.

- Servers usually include lots of fancy status lights to indicate system activity. But aside from the XServes, Macs typically don't include hard disk activity lights. Apparently there's a way to hack an IDE cable with this functionality, but I'm not quite brave enough for that. I'd also like to be able to see the D-Link card's Tx/Rx activity LED transfered to the front of the case. Again, it would require some brave/foolhardy resoldering.

- I know that some people will be balking at the fact that the machine clocks at 400MHz. One has to remember though that the G4 is a very powerful processor (for its generation). With OS X the system really is just as responsive as the 1.8 GHz Celeron / Windows XP system it's replacing. However, in the future if we need more power there are plenty of socket-based upgrades available for this system. If desired we could even bring the system up to a Dual G4s running at 2.0 GHz. For now though, the system is fast enough.

I placed the new server in the bottom slot of our cabinet, some of our other equipment sits on top of it.

I have to admit that I was quite surprised that nothing went horribly, terribly wrong with this mod. I think that probably my fear that the project would fail horribly (forcing me to admit my shortcomings to my bosses and offer to soak the cost the materials I'd purchased) kept me on the straight and narrow with my planning and measurements. Years of debugging various systems at work helped me realize that there would probably be a firmware update for the G4 tower to overcome the mysterious freezes. Overall, it's been a very enjoyable project, and the fact that the system is humming along with almost no issues to date (except for the ones which can be traced back to its users) gives me a great sense of pride.

External Resources:

Accelerate Your Mac: G3 ATX Conversion
Accelerate Your Mac: A G4 system in an ATX case
MacMod: Silent ATX G4
MacGurus: AGP G4 Motherboard Layout