Power
Supply Exchange
15"
Flat Panel iMac
**DISCLAIMER**
Altering any part of your OS or computer will void your warranty
and may damage your computer. These modifications are for
educational purposes only and are performed at the owners
risk - This site or it's owner are not responsible for any
damage caused.
This
particular iMac (15" 800MHz, Superdrive model M8535LL/B)
was the victim of a power surge so needless to say it was
in need of a replacement power supply. Getting a hold of one
was a little difficult but I ended up finding one locally.
The part number is 922-4688.
Tools
Required
-
Phillips #0 screwdriver
- Torx-15 screwdriver
- Torx-10 screwdriver
- Thermal Compound
- Anti static wrist strap
Step
1
Place
the iMac on its side resting the face of the screen on a soft
surface - a towel is fine. Use a Phillips #0 screwdriver to
loosen the 4 screws on the underside of the iMac. Note: these
screws will not detach from the base so don't force them out.
Step
2
Remove
any RAM and Airport cards at this point (to avoid damage)
and continue to remove the 4 visible torx screws using a Torx-15
screwdriver
Step
3
Carefully
ease the base towards you to detach it from the body of the
iMac. There will be wires attached to the base, I recommend
you disconnect the majority of them to reduce the clutter.
At this point you need to remove the optical drive assembly
as the power supply is above it. Use your Torx-10 screwdriver
for this task. In the picture below, the two screws on the
far right secure the EMI shield, it also has a strip of copper
tape that holds it on the optical drive. I prefer to release
all screws and remove the drive assembly with the EMI shield
in place, if it makes it easier for you to remove it from
the optical drive simple peel the tape off and reapply when
reinstalling everything.
Step
4
After
you have unscrewed the drive bay, disconnect all wires (power,
ATA, etc) and remove the drive from the chassis. You should
now see the underside of the power supply. The power supply
itself is two separate PCB's joined by wires. The right side
is secured by 4 screws, two of which are hidden behind the
optical drive door. I suggest removing these first before
anything else. In order to do this you must open the drive
door and unscrew the Torx-10 screws through the opening shown
below.
Once
these screws have been removed, proceed to remove the 4 remaining
Torx-10 screws to unfasten the power supply.
Ouch....
Step
5
After
you have replaced the faulty power supply simply reverse the
disassembly method. There is one step in the assembly that
is extremely important. There is a heat pipe that transfers
heat from the CPU to the upper chassis of the iMac. It is
imperative that both of the contact surfaces are cleaned and
a fresh dose of thermal compound is applied to prevent the
CPU from overheating. This step cannot be missed and MUST
be followed.
additionally,
when replacing the main base, Apple recommends that the 4
Torx-15 screws are tightened to 17in.-lbs of torque using
a torque driver. If one is not available, they can be tightened
by hand FIRMLY, BUT NOT FORCIBLY. This ensures a firm contact
between the two surfaces illustrated above. If the screws
are too loose this can potentially result in a damaged CPU.
Additional
Info
The
iMac uses a Panaflo fan. Apple can use good fans if they want,
they usually choose not to though :-( This particular model
is rated at 30.0dB @ 2450rpm
and
a shot of the CPU
