Installing a fan in the G4 Cube

Many Mac purists out there will shake their heads and disagree vehemently, but with spares for the remaing cubes starting to thin out, a fan is essential in keeping your cube healthy, and I heartily recommend one to anyone who uses their cube for more than a couple of hours a day.

The Mac G4 Cube was designed to hold a fan. Even though in it’s original incarnations (450MHz and 500MHz varieties), there was no fan installed, the case itself has a place to hold an 80mm fan of about 20mm thickness and with a little effort, one can crowbar a 25mm thick fan in for more effective cooling.

Be careful when selecting the fan. The one I bought was a silent, solidly built one which had supporting tubes around the corner mounting holes. It seemed like a good idea at the time. However, these turn out to make installing the fan without disassembling the whole case impossible. A lighter fan without supports on the corners would have been much easier to install. In any case, I used a hacksaw and cut two adjacent supports along the edge which eventually ended up towards the back of the Cube.

I bought myself a nice, quiet 80mm x 25mm 1900 RPM fan. They tend to be about 3~6db quieter than 20mm fans which push the same amount of air. It came with 3 wires, red, black and yellow

Replacing the fan is actually a little more time consuming than replacing the hard disk, but not really much more difficult.

You’ll need a set of Torx drivers for the star shaped “security” screws. Sizes T8, T10 and T12 should do the trick. You will also need a medium sized pair of pliers for some minor and painless case modifications.

Opening the case:

      First make sure you have the fan, the torx drivers and enough room to work on,  i.e. a flat, clear surface within easy reaching distance.

• Unplug the Cube and invert it. Take care not to scratch the machine’s plastic case. I inverted mine onto a pillow.
• Push the rectangular, inset bar located on the upturned base in firmly, until you hear it click. Now release it. The handle should pop out.
• Use the handle to lift the chassis out of the upturned case. If this is the first time it has been removed, it might take a little teasing to get things moving.
• Lift the chassis out vertically, taking care not to scratch the insides of the case with the metal corners of the chassis. The chassis has no sharp corners so this is not a serious issue. Still, it would be a shame to scratch it.
• Now place the chassis down on a flat, clear surface. Take care not to damage the sensor on the top of the unit (probably facing downwards since it’s the side opposite the handle).
• Push the handle in all the way and let go. It should stay in place.
• Turn the case, so that the sensor is now facing upwards.

Opening the chassis

In order to put a new fan in without a complete disassembly, it is necessary to remove the optical drive.

• Remove the top plate by taking out the four corner bolts and two bolts on either side.

• Lift off the top, slowly and remove the small cable which connects the power sensor to the chassis.
• Place the top panel somewhere level, avoid touching the sensor.
• Now slide the plate with the orange spot on it slowly up and out, revealing the optical drive.

You should now see the drive exposed as the picture below shows. 

• On either side of the drive, there are some screws, holding it in place. Remove these screws on the sides of the optical drive to release it.
• Slide the drive upwards and remove the power and ATA cables from the connectors.

• The drive can now be removed, revealing the gap at the bottom of the case for the 80mm fan.

Installing the Fan

• In order to slide the 25mm fan into the case without disassembling the whole thing, we need to bend the fan supports out to the sides until they allow the fan to slide in.

• Note that there are two further holders at the rear of the case which may prevent your fan from fitting.
• If your fan has corner posts around the holding bolts, remove two of them to allow the fan to slide into place. 

• Bend the supports back around the fan to ensure a snug fit, as shown in this example picture below.

• After playing around with the supports for a bit, I taped around the fan with duck tape after breaking the two back posts. This also helps reduce vibration noise, but this is not necessary.

Connecting the fan to the power

It’s now time to connect the fan to the power supply. We will use the optical drive’s power supply which we have at hand since we removed the optical drive.

• Remove the little cover from the back of the optical drive’s power connector.
• You should see four cables leading into the connector.

This big connector has the ability to generate 3 different voltages, 5v (slowest), 7v and 12v (fastest). Depending on your noise tolerance and the power and voltage rating of your fan, you may find any one of these three voltages suitable. This I will leave for you to experiment with.

Note, if your fan has three wires, one of them is unnecessary for this modification. You will have to determine which two wires (usually red and black) are the power wires and which one connects to the sensor.

The table below shows how to harness any of three voltages from the optical drive’s chunky 4 pin power connector. 

	Fan Wire 1 (Black)	Fan Wire 2 (Red or Yellow)
Fan at 5V	Molex Ground (Black)	Molex +5V (Red)
Fan at 7V	Molex +5V	Molex +12V (Yellow)
Fan at 12V	Molex Ground (Black)	Molex +12V (Yellow)

For example, to run the fan at 7V, connect the fan’s black wire to the +5V (Red) connection and the fan’s red/yellow wire to the +12V (Yellow) connection. You can connect the fan’s RPM wire directly up to the motherboard. Unfortunately, on the Mac, the wires are all black! Check the photo to confirm the voltages.

• Cut the power cables of the fan to a decent length, you won’t need the connector. You can discard the sensor wire on a three wire fan.
• Use a knife or other tool to push the cables strongly into the drive’s connector without damaging the metal “blades”. These blades should cut through the rubber insulation on the cable and create a connection with the copper wire itself.
• If the cable comes out, your fan will stop. This will be very difficult to spot later, unless you install a fan with an LED or other indicator, so confirm that the cable is tightly held before reassembling the computer. 

• Don’t forget to replace the plastic cover.

Putting things back together

• First the optical drive’s data and power cables.
• The optical drive’s holding screws.
• The power button’s wire connecting the top plate to the chassis.
• The chassis top plate with its 8 screws.
• Upturn the chassis carefully and pop out the handle
• Carefully return the chassis to the case, making sure not to catch anything, and push the handle in all the way until it clicks.
• Turn the computer over, connect it up and restart.
• Confirm the fan visually, by listening or by holding your hand over the top vent.

Congratulations, your Mac G4 Cube just got even cooler!