Step 7: Replace the Hard Drive and Reassemble the Carrier Assembly
Reassembling the iMac mostly requires working backward through the steps you followed to disassemble the computer. After screwing the new drive into the bracket, attach its data cable. Replace the white wrapper, carefully smoothing it down as you go.
Thread the video and AirPort antenna cables through the cable clip and reattach the power connector to the hard drive. Push the carrier assembly back into place. Be sure the data cable that attaches to the iMac’s motherboard is not trapped beneath the assembly.
Replace the four carrier-assembly screws, put the EMI shield into position, and press the copper tape onto the optical drive. Replace the two EMI shield screws.
Step 8: Apply Thermal Paste
A thermal pipe inside the iMac draws heat away from the processor and vents it through the base of the computer
. The outlet for this thermal pipe sits flush against a mating surface (where the two parts meet) attached to the upper part of the iMac’s base
. Between the thermal pipe and mating surface is a thin coat of silicon paste (known as thermal paste or heat-sink compound). This paste—available at electronics shops for around $5 a tube—helps eliminate air gaps between the surfaces, so heat goes out the pipe rather than into the iMac.
When you separate the bottom housing from the base of the iMac, you break the thermal seal. You must restore it with a fresh coat of thermal paste when you reassemble the iMac.
To do so, first scrape off the old thermal paste from both surfaces with the edge of a credit card. Don’t use an abrasive material, since it may score the surfaces and create gaps that prevent the connection from sealing properly. Also avoid liquid cleaners—they could damage the iMac’s internal parts. When the surfaces are clean, smear a thin layer of thermal paste on the mating surface and spread it evenly
. Remove any paste that gets in the vent hole.
Step 9: Reattach the Bottom Housing
With the iMac thoroughly pasted, reattach the grounding cable, the video connector and its cover, the AirPort-antenna connector, the AC-line filter connector, the hard-drive and optical-drive data connector, and the rectangular power connector. Then replace the screw that holds the grounding cable in place. Important: Tuck the cables inside the iMac’s base—if you pinch the power cable between a screw post and the edge of the housing, you could cause a short that will destroy your iMac! Push the bottom housing into place and screw in the four Torx-15 screws. To ensure a tight seal, tighten these four screws so they’re firmly in place (but not so tight that you can never loosen them).
Install the RAM module and AirPort card that sit beneath the user-access plate, attach the Air-Port antenna, and then screw the plate back into place.
Editor’s Note: This article was written with assistance from