iMac G4 (USB 2.0 / 2003.09) 167Mhz Bus Model Overclocking


Here is a short overclocking manual for the 166Mhz busclock iMac G4 models:

* * * W A R N I N G * * *

If you don´t have soldierd on any mainboard you should not do the following modification.

Apple warranty is lost if you do overclocking.

By reading this manual you accept to do the modification on your own risk,
Ethernetworks will not pay for any damaged mainboard.


Touch the central heating, a gas line or any metal contact to set your body to ground. Wear only cotton cloth and anti static shoes (Birkenstock). Never touch any chip pins directly.


unscrew the iMac top cover.


Remove all connectors from the mainboard. The video connectors plastic cab is glued, remove it with a long lever.


Remove the PowerPC 7445 heat pipe. It´s only jamed by the bracket.




locate the Motorola PowerPC 7445 PLL settings resistors on the mainboard near the processor.
They are in the blue frame.


Here is a closer view:

The resistors 374 - 383 clock the PPC 7445.
The picture shows the resistor positions for 1250 Mhz (7.5 x 166Mhz)

Here you can find the Processors user manual for all the settings (chapter 1.9.1 PLL configuration)

PLL Resistors set Multiplier Bus Clock Speed
10010   5.5 166 Mhz 923 Mhz (iMac 15" default)
11010 R374
6x 166 Mhz 1000 Mhz (iMac 15" default)
01010   6.5x 166 Mhz 1083 Mhz
00100   7x 166 Mhz 1166 Mhz
like the photo
7.5x 166 Mhz 1250 Mhz (iMac 17" default)
11000 R375
8x 166 Mhz 1333 Mhz
01100   8.5x 166 Mhz 1400Mhz
01111   9x 166 Mhz 1500Mhz

STEP 5: Solder the resistors the the position according to your speed wishes.


We tested 2 Machines.

iMac G4 1000 15":

clocked to 1333 Mhz it works but freeze after 40 Minutes

clocked to 1250 Mhz it works fine.

clocked to 1000 Mhz it works fine.


iMac G4 1250 17":

clocked to 1333 Mhz it works but crashes after 10 Minutes

clocked to 1250 Mhz it works fine.

clocked to 1000 Mhz it works fine.


STEP 6 assembling

Do all in the reverse order. Take care that the heat pipe is mounted correctly ! Without heat pipe the CPU will life only for about 8 seconds. Also care about the cables, dont wound any of them.


That´s it so far, if you have some infos about the 133Mhz iMac overclocking or tips and hints feel free to send us e-mail. Also mail us what settings are working with your Machine.

here you can find full photos of the Mainboard (800kB each): top back

This page helped you ? So, why dont you donate me via PayPal


Regards and lots of fun


Your Ethernetworks Germany Team


More Overclockin Links:

Tak´s Homepage

Leo Bodnars´s Homepage






Server - Router - Hubs - Switches - Software - Contact - Support - Hardware - FireWire - USB - Apple

Es gelten unsere Allgemeinen Geschäftsbedingungen, Lieferung solange Vorrat reicht.
Bitte laden sie unsere AGBs runter:

Bestellen Sie per Telefon: 0700-ethernet oder 0651-991892-10
per Fax: +49 (0)651-991892-20
oder via e-mail an
Here is the English version of our webpage.

alle Preise inkl. ges. MwSt, solange Vorrat reicht
©2002 Ethernetworks, Trier - Germany