You can look at
www.xlr8yourmac.com they have a lot of CPU swaps if you look at the user reviews of CPU upgrades and shoose "Apple".
The first snag is that the dual 500 is on a 100 Mhz bus while the 1 GHz is on a 133 or 167 MHz bus so the bus clock ratio has to be adjusted and that is made by soldering on SMDs and that is very tricky. I think that some supply woltages have to be adjusted as well.
Here is one that I dug out, I am sure there is more, but is quite extensive work...
Reviewer's Name: Jeffrey
Date Submitted: 6/12/2003
Rating (1 to 10): 8
Manufacturer: Apple
Rated Speed (CPU/Cache MHz): G4 867MHz Quicksilver model
Max Speed (CPU/Cache MHz): 900MHz
Cache Size: 1MB
Mac Type: G4/400MHz
Comments: I successfully installed a QS867/133 in my AGP400/100. I chose to keep the M/B at 100Mhz and increase the multiplier to run the processor at 900MHz. The information needed to do this can be found at this fantastic XLR8YOURMAC site. (Note the 12V connection difference in the QS modules vs the older AGP towers - see FAQ's Apple G4 section for info.) The only thing I was missing was a current photo of which resistor to add/remove. Thanks Tycho for this info!
I have never soldered electronics before, but removing the resistors from the daughter card to change the multiplier from 6.5x to 9.0x was not as difficult as expected. It was nerve-racking knowing that I could ruin it, but it turned out OK. Boy, that first startup chime was a relief!
It was more difficult to remove the ATA33 connector from the M/B and bend the pins over to clear the bottom of the daughter card. I moved the DVDROM and a second hard drive to an ATA100/133 PCI card. The only other necessary change was to add a +12V source to 4th mounting hole on the daughter card.
I did make some other mods since I was mucking about anyway. I added 512MB of RAM and an ATI8500 video card. I pulled out the stock 220W power supply and added a PC 350W ATX supply (details are also at XLR8YM). I did this knowing the new CPU draws more juice, and that I want to add a CDRW and two additional hard drives as money permits. One can never have too much power!
In addition, since I was not sure if the stock 400MHz heat sink could keep the new CPU cool, I made some cooling mods. I cut away the finger guard from the 120mm fan in favor of a wire one, added a shroud to itsĖ intake to improve air flow, and added another fan to blow directly on the heatsink. The fan was free as it came from the original power supply. So far, this set up has performed fine. I have no way to check temps, but the heat sink remains cool enough to touch.
Overall, the whole system is noticeably more responsive. I have not seen any compatibility issues. Well worth the time and effort.
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