iFixit

Use the attached black tab to pull the data display cable connector away from the logic board.

Remove the eight 12 mm T8 Torx screws securing the display panel to the rear case.

Lift the display panel from its left edge and rotate it toward the right edge of the iMac.

With the display panel still lifted, disconnect the four inverter cables.

During reinstallation, place the four inverter cable connectors in voids between components attached to the rear panel so the display panel will sit flush.

During reassembly, the order of the inverter cables is interchangeable within each socket.

If you are replacing a hard drive and have an extra set of hands, it is possible to reach in and remove the drive without disconnecting anything but the LCD temp and display connector in the previous step with the LCD in its propped position.

The next few steps bring your hands close to the exposed face of the power supply. Do not touch the face of the power supply to avoid a high voltage shock from the many large capacitors attached to the board.

Remove four T10 Torx screws securing the power supply to the rear case.

Two fine-thread 7 mm T10 Torx

Two coarse-thread 7 mm T10 Torx

Rotate the top edge of the power supply slightly away from the rear case.

The single-wire connector near the upper left corner of the power supply is small and held very tightly in its socket, making it inherently difficult to remove. Be sure to pull only on the connector during removal, as pulling the cable will surely cause it to break.

The single wire shown in the first photo is for the power supply temperature sensor. If you have power supply temperature issues after installation, check this connection first.

Grab the connector between the nails on your thumb and index fingers and pull it toward the top of your iMac, disconnecting it from the power supply.

Rotate your power supply toward the optical drive.

Disconnect the DC power cable by simultaneously depressing its lock mechanism and pulling the connector away from its socket.

It may help to wiggle the connector while pulling it away from its socket.

Disconnect the AC-in cable by simultaneously squeezing the cable lock and pulling the connector away from its socket.