Breaking The Speed Limit! -
Instructions To Hotrod Your iMac To 300Mhz
by Kevin I. Glattfelder
iMac Overclock
The iMac is a wonderful machine that has opened up an entirely
new group of people to the computer age. The iMac was designed
for those who wish to enjoy the benefits of owning a computer
and access to the internet without the hassles involved when
dealing with PCs. While a large number of the machines were
purchased by newbies a large number were snatched up by weekend
hackers. The following procedure will show you how to overclock
a Revision A iMac.
Warnings
The actual procedure is fairly difficult. It requires extreme
skill and knowledge of soldering techniques. If you have never
soldered on PC boards and chips I would not suggest attempting
the procedure. The devices that need to be moved are very
delicate and are approximately 1/16" X 1/32" of
an inch in size. The PC board is also very delicate, too much
heat and force and the solder pad will lift. Don't attempt
this procedure if you have any reservations about your abilities.
PLEASE NOTE THAT BY MODIFYING THE CLOCK SPEED OF THE MACHINE
YOU WILL VOID YOUR WARRANTY
Helpful Links
Before performing the procedure point you browser at the
following link.
The first link has a table that shows the various positions
of the four surface mount resistors and what clock speed they
set. The second link gives a very detailed pictorial of how
to dismantle an iMac and remove the CPU daughtercard. Study
them and print a hard copy if possible.
Tools
You will need the following tools to perform the modification:
-Work table with a clean surface preferable white (so you
can see the resistor(s) when you drop them!)
-Standard wattage soldering iron (15-20 watts) with a small
tip, a tip cleaning sponge and a base would help.
-Solder
-Fine tip forceps (plastic would work well)
-Anti-static wrist strap (grounding strap)
-Well lit room
-Steady nerves
Procedure
First decide what speed you want the CPU to operate at. I
have been overclocked to 300 MHz for nearly three months without
any problems (it would not run any faster). Use link one to
find the proper resistor combination for the chosen clock
speed. Next follow the steps shown in link two in order to
remove the CPU daughtercard. Flip the board over and locate
the four resistors. Place the board on the work surface and
secure it so that it will not move around. Plug in the soldering
iron and allow it to fully heat. Make sure the tip is clean
and test the temp by touching solder to it. The solder should
melt instantly. When the iron is ready touch the tip to the
lead of the first resistor that requires moving. Heat the
resistor (don't apply any pressure and don't slip the device
around) until the solder on the board melts. Use the forceps
to remove the resistor (take your time and be careful not
to pull too hard on the resistor). Place it in the adjacent
position and use the forceps (I used my finger nail because
metal forceps sink the heat away) to hold the resistor down.
Solder each side of the resistor. Make sure that solder does
not bridge to any other pad while performing the procedure.
Once all of the required resistors have been moved double
check your work. Make sure that the resistors are in the correct
position and nothing is shorted. Reassemble the machine making
sure that the CPU daughtercard is fully seated. Don't put
the cosmetic back panel on yet. Plug in the power cord and
the keyboard. Press the power button and wait for the machine
to boot. If it bongs then that is a very good sign!! Allow
the machine to boot and check for proper operation. BTW if
you have the PowerLogix G3 Cache control program make sure
it is turned off before performing the procedure. The machine
may lock up while loading the control panel if the ratio is
set too high. My cache runs at 150 MHz not any higher. The
CPU will run hotter than before. One way to cool the chip
is to remove the thermal sticker from the top of the processor
and replace it with a thin film of heat sink compound.
MacBench 5.0 results expressed as the percentage
of improvement over the base machine
Actual MacBench 5.0 Scores
.
Processor Score
Floating Point Score
iMac G3/233
719
790
iMac Overclocked to 300Mhz
908
933
Power Macintosh G3/300
1000
1000
Good Luck!
If you take care when performing the procedure you can have
a very fast machine. Macbench 5.0 scores rival and in some
areas exceed those of the benchmark G3 300 machine.
Kevin is a recent convert to the Mac having worked on PCs
most of his life. On his way to buy a Dell he was sidetracked
by an iMac and has been a reformed Wintel user ever since.
Much more than an iMac "new user" statistic Kevin
works in the semiconductor electronics industry. If you have
any questions or hacks you are welcome to send
him e-mail.
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iMac Overclock
