Loosen front bezel from the rest of the assembly slightly. Do not
remove bezel completely.
the top of the bezel is held in my two latch mechanisms that can only
be accessed with a plastic card and some luck.
the latches pivot when the card is inserted upward into the rear
ventilation slot of the imac at just the right angle.
pushing the card in and forward (toward the front of the computer)
makes the latch release and the bezel can be separated from the rest
of the assembly with some persuasion.
Each side has to be done separately. This is probably the most
difficult part and can take about thirty min of fiddling if you have
not done it before.
Once the bezel is loose gently separate it from the chassis and
disconnect the microphone cable and camera.
You should now be looking at the bare LCD and a black EMI shield
across the bottom.
The black EMI shield is glued into place with tape, separate it from
the bottom of the metal chassis along the bottom edge. Be careful it
tears easily.
A non marring plastic stick is very useful for this - like this Nylon probe (sometimes local stores like Radio Shack may have something similar)
Similar black EMI tape is around the sides and top edge of the LCD.
Unstick it but do not tear it off or remove it.
Lay the iMac flat on its back. there are four T9 torx screws holding
the LCD assembly to the rest of the chassis, one in each corner. They
are difficult to see and you may need to bend the plastic sides of
the rear bezel out of the way to see them clearly and remove them.
Disconnect the video data cable from the MLB (main logic board), it is held in by two
T6 torx screws.
On the 17" model there is also an inverter cable that is plugged into
the MLB near the right speaker, unplug it.
On the 20" model you should now be able to tilt the LCD away from the
rest of the chassis slightly until you can see the inverter cables
that connect the LCD/inverter to the power-supply. Disconnect the
bottom two.
Tilt the display away from the chassis to about a 90 degree angle,
disconnect the top two inverter cables.
Remove the LCD display and set aside.
You should now have a clear view of all the major components of the
iMac.
A Hard Drive replacement is trivial at this point. most Drives are held in
via a latch mechanism or two torx T9 screws. Remove the old drive
and move the thermal sensor and brackets to new drive and re-install.
The ODD (optical disc drive) drive is held in place by an awkward
latch mechanism as well. Two plastic tabs on the bottom and top of
the drive can be loosened with some persuasion with a flat head screw
driver.
To replace the CPU the MLB must be removed. At this point you should
decide if you want to continue with disassembly. The connectors for
the thermal sensors, speakers and iSight are difficult to remove and
easy to break. Look at the placement of the cables, if they are not
routed properly they are easy to pinch and cause shorts or other damage.
Memorize or take pictures of the cables you disconnect.
There should be these cables:
- HDD Fan
- Optical Drive fan
- CPU fan
- Optical Drive thermal sensor
- HDD thermal sensor
- Power button
- ALS sensor
- Speaker/iSight/Mic cable
- IR sensor
- Optical Drive flex cable
- HDD SATA cable (this may be UNDER the MLB on some models, we'll get
to that)
- power supply cable
Around this time you will also have to remove the speakers (torx T9
screws), the airport/BT card (torx T6 screws), IR assembly (torx T6 screws).
Some cables/connectors hide under the speakers.
You should now be able to see all the Torx T9 screws that hold the MLB
in place, depending on the model there are about 7 of them.
Do not remove the screws holding the metal heatsink assembly to the MLB!
Depending on the model there may be two small torx T6 screws holding
the top of the heatsink fin assembly to the rear of the chassis,
remove them as well. The screws are a mix of coarse thread and
machine screws of varying lengths, make you remember where they go.
You should now be ready to separate the MLB from the chassis.
WARNING: the MLB is very delicate. It is an odd shape and has some
very thin sections that are easy to flex. Bending or flexing the
board will cause the solder joints on the chips to BREAK! This
includes VRAM and on-board ram as well as everything else. If you
damage the board or the connectors on it you will have a very
expensive paper weight! These parts are not available for purchase!
You should be able to pry up on each side of the board until it
becomes loose. At that point you should be able to grasp it by the
sides (NOT by the metal heatsink assembly) and see if you have any
more connectors on the UNDERSIDE of the MLB (the 17" model has the
power supply connector underneath). This is extremely difficult to do
because the attached cables only have about 1-2 inches of slack.
With luck you should have the MLB free of the chassis.
Once the MLB is free take a look at the heat sink assembly. the GPU
and CPU have separate heat pipes, cooling fins and are two separate
pieces. Locate the CPU, it should have a plastic socket underneath the copper
heatsink assembly, the GPU does not.
Remove the 4 torx T9 screws that hold the CPU fin assembly to the
GPU half.
Remove the 4 torx T9 screws that hold the copper heatsink to the
CPU. The philips #2 screws on top of the heatsink are captive and do
not come out.
You should now see the cpu die itself which is removable by twisting
the retaining screw/latch with a philips #1 screwdriver or smaller.
this screw is plastic and easily damaged.
Reassembly is the reverse.
Don't forget to wipe the new CPU and heatsink clean with alcohol and add fresh thermal paste.
When re-installing the MLB it is easy to pinch the cables for the fans and thermal sensors between the bottom of the MLB and the
standoffs for the screws. Double check these before tightening anything down.
As you can see this project is not for the faint of heart.
I do not have any pictures to aid in this but there are some visual
guides online that may help you:"
