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1/27/06 News Story DetailReturn to News Page

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Dual G4 533MHz Overclocking
By Chris Placzek

Warning: As with any overclocking or hardware modifications, do this at your own risk and it may not be reliable. DO NOT attempt this unless you're willing to accept the risk of failure and repair costs.

I was asked by someone to over-clock their dual 533MHz. I did some research online, figured out how to do it, and decided I would try for 600MHz. The cache chips on this are rated for 275MHz, and this modification would over-clock them to 300MHz. I have done this successfully with a single 533MHz 7410, so I expected that the dual version would run at 600MHz also. Turns out I was correct.
The first thing that should be done is changing the multiplier settings. In a 133MHz bus Mac, your options are 533, 600, 667, 733, and higher. With some extra cooling of both the processor and the cache chips, and a good voltage boost to the processor and cache chips, Im sure 667MHz would be achievable. Note, extra cooling could be a powerful water-cooling setup or better. Take a look at these pictures for the location of the resistors which control the multiplier, the areas to be working on are grayed out:

On the back of the card, look center and below slightly of the cache chips for the multiplier, and below and to the right for the resistor which controls voltage to the L2 cache.

On the front of the card, look below the left most mount point for the multiplier.
Assume that on the back, cache chips being on top, from top to bottom, the resistors are 3,2,1,0. On the front of the card, cache chips being on top, from top to bottom, the resistors are 0,1,2,3.

Instead of actually soldering on resistors, I use conductive paint.

Now, in my experience, a voltage boost to the L2 cache will also be required. But, you can test out the card with no voltage boost if you'd like. I have heard of people not needing a voltage boost on a single 533. If you look at the first picture, there is another grayed out area containing R51 and R52. By removing the 124ohm resistor at R51 and adding a 100ohm in its place, voltage going to the L2 cache chips is boosted from 2.5V to 2.82V, and the cache chips are rated to handle 2.9V. If you want to try different voltages, the equation can be found at xlr8yourmac at the Mac Mods/Upgrades page, G4 Macs section articles on running a single G4 533 in a Sawtooth as well as the article on the G4 7400 module. (Info/Equations are in this article on Digital Audio G4/533 CPU module in a Sawtooth, which also used heatsinks on the L2 cache. He reached 650MHz CPU, 325MHz L2 cache speeds on that single CPU sample, but YMMV.-Mike) Unfortunately I didn't take a picture after I finished the voltage boost, but the resistor leads went between C103 and C132.

I'd also like to note that if you want to use this module in a Sawtooth or Mystic, you would have to remove the CDs IDE connector. Also, the heatsink for the dual 7400 processors (on previous models) would not work on the dual 7410 without some serious modifications. The legs don't even line up with the holes on the board. Best bet would be to modify the dual 7410s heatsink to fit, or modify the case itself to allow the 7410s heatsink to fit unmodified (this option providing much better cooling). The 12V mod would not be required. (FYI: He's referring to the 12V DC mod/connection required to use Quicksilver CPU modules in older Towers. See FAQ's Apple G4 section. BTW - Some Sawtooth owners using OEM Apple CPU Modules w/L3 cache have reported the L3 is not enabled when used in a Sawtooth. Several reports on that from readers that used Quicksilver modules in a Sawtooth systems for instance-Mike.)

The machine is totally stable at dual 600MHz. If anyone has info on boosting the voltage to the processor itself, feel free to share it with me and I can add it to this article. And if anyone tries for 667MHz, or tries this module in a Sawtooth, I'd love to hear about it.
-Chris Placzek

I thought Leo had run some modified Dual 533s at more than 600MHz, and he replied with details below-Mike)

" Hi Mike, (Leopold Porkstacker here)
I read the dual 533MHz G4 CPU module overclocking story, and wanted to add that back in 2002 I successfully overclocked my dual 533MHz 7410-based G4 CPU module to dual 667MHz with the help of voltage boosting (I think I had them pegged at 2.1V - I need to verify this though) in conjunction with a custom fabbed heatsink setup (which I have had in my posession since 2002) coupled with a 40W Peltier cooler and an even beefier Thermaltake Volcano 7+ solid copper heatsink (Dremel Tool modified for clearance of the three 3" long screw/nut/washer/spring custom clamps).
Additionally, I changed out Tycho's aluminum coldplate with a 3"x1.5"x0.5625" copper coldplate which makes contact with both CPUs. The thing ran flawlessly under full load, that is, until I was meddling around with the internals one day when I accidentally destroyed a vital PCB pad on the dual CPU daughtercard when my 8mm box wrench (used for fastening the nuts to secure the CPU card in place) slipped. Ooops! Anyhow, I thought I'd share this information.

Some images of the setup (unfortunately minus the Peltier/heatsink combo) are here:
(Links to pix disabled after linked .mac pages were removed/404)

  • Pix 1
  • Pix 2
  • Pix 3 (closeup)
    (the DIP switch bank was used to control the PLL_CFG on the fly - obviously while the machine was powered off).

    Oh, and this page:
    homepage.mac.com/leopoldporkstacker/.Pictures/lowpixelcount/overclock.html [.mac now RIP]
    shows some general Mac overclocking madness I was responsible for.
    -he who stacks pork"

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