iMac ATX

Cutting the box/enclosure

The cut-out for the PSU and its fixations are simply done by tracing appropriately on the case (that's one of the reasons I used a transparent plastic box), then I drilled around.

... and used a cutter to finish. After that, I used a file to smoothen the edges.

Once the PSU is in place, we'll put the logic board assembly in position to mark the fixation points on the bottom of the box, as well as the apertures for the various connectors, using the same technique as for the PSU. Don't forget to drill some holes for the power switch and the optional LEDs.

Now that we're done drilling and cutting, we can proceed with the actual assembly.

 

Wiring.

The detailed wiring diagram is available as a PDF at the end of this article.

We will start with the PSU. We'll cut the ATX and the 12V P4 connectors (leave some length). We'll use some of the orange wire to fork one of the 3.3V wire of the PSU (see picture). We'll use thermoretractable sleeves to insulate all bare wires and contacts. We'll solder the wires of the PSU to the pins, which we'll then gently flatten with a pry to fit them into the connector.

The ATX PSU is normally switched by a command sent by the logic board, but since PC and Mac differ (The ATX unit will be turned on by a low level signal (ground), whereas the iMac triggers a high level signal of 5V), we'll need to make an inverter to adapt the PFW signal. For that, we'll use a 4069, which is a 6x inverter. We'll put the chip face down, pins up. Next we'll fold or cut the pins as they are on the picture. We'll use green, bleu red and black wires from the PSU to hook it up.

We'll then solder the wires according to the picture, and we'll place the little dude in a thermoretractable sleeve.

The IDE flat cable and the VGA cable will be modified according to the PDF document. Be careful and gentle when fitting the connectors.

We'll hook up the LEDs to 120 ohms resistors. Once everything is soldered, do not forget to insulate the same with some thermoretractable sleeve.

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To go even further, we can hook up some LEDs to the logic board for monitoring the hard drive and ethernet activity. This is strictly optional and somewhat high profile. For the hard drive, we'll solder some metal (bridge) on the point "R492" on the backside of the logic board. The LED will be soldered on the face of the logic board. The anode is the red wire and the cathode goes on the brown wire.

For ethernet, we'll solder bridge in place of R288, R287 and R284 on the backside, the LEDs will go on the face, next to the PHY of the Broadcom ethernet controller.