Home > Mac, mods, Technology > Installing Powerlogix 1.5GHz 7447A CPU Upgrade for Power Mac G4 Cube

Installing Powerlogix 1.5GHz 7447A CPU Upgrade for Power Mac G4 Cube

I bit the bullet yesterday and upgraded my Power Mac G4 Cube from its original 450MHz processor to an overpriced 7447A Power CPU in the form of a Powerlogix CPU Upgrade.

First up, I had intended to purchase a chip with a VRM bypass but when it arrived, I found that I’d mis-ordered and got a vanilla version without.

I checked the website more closely and yes, indeed the version I had ordered did not have the VRM.

I would have sent it back, but unfortunately, I ordered it from OWC in the US, so that’s not going to happen.

Here are some extra hints if you want to replace your CPU with a Powerlogix one. These are not complete instructions in and of themselves.

Before you start, watch the video and print and read through the instructions. They are clear on most counts but I found a few areas lacking.

Here I’ll list a few of the difficulties I faced while also listing the outline of the instructions

Firmware Update
(in a nutshell) 

  • Insert the CD with the Cube powered up. Then shutdown the Cube
  • Now hold down the programmers button and keep it held until the power light flashes rapidly then press and hold C until the firmware screen appears.
  • At the menu
  • Press 4
  • Wait for the process to complete.
  • Press 5 if you use OS 9.

 Now this bit was a bit worrying, nothing was mentioned what to do after the above steps. 

  • Just press the option to shut down the Cube
  • Proceed with the disassembly.

Graphics Card and VRM

  • Ground yourself.
  • Remove all cabling.
  • Pop the chasis.
  • Remove the top plate.
  • Be careful with the power connector between the top and the chassis. It’s quite short.

    fig 1

    You do NOT need to disassemble the whole chassis in order to remove the CPU.

    • Just turn the cube on its side (GFX card up) and remove the two posts. Remember which way they go, they look very similar but won’t fit if you get them in the wrong place or the wrong way around!

      fig 2

      • On this side of the motherboard, you only need to remove three screws. 

        fig 3

        Removing the Video Card

        The first real challenge you will encounter is removing  the video card. The cube is tight and the card is connected to a riser from the motherboard rather than directly to the motherboard itself.

        • MAKE SURE YOU’VE REMOVED THE TWO SCREWS that hold the GFX card to the frame. They are located on the base of the Cube and flank the VGA and ADC connectors.
        • Remove the Video Card and Riser card together. It’s not possible to remove the card by itself.

          The main difficulty is that the ports are stuck through holes in the base, which prevents you from lifting the GFX card and riser vertically, you have to lift just the point shown below.

          Don’t worry, the connector is quite tough and the angle won’t break any pins or edge connectors if you are careful.

          Try not to lift the GFX card out too far at first and be careful of the wires connecting the GFX card to the motherboard.

          If you are having difficulties with the GFX card assembly, you might want to remove the VRM first, which is considerably easier to get out.

          fig 4

          The black connector shown below comes off easily. Just push down on the protruding part of the clip like a clothes peg and pull the clip out.

          fig 5

          Try as I might, I was unable to remove the brown connector shown in the picture above.

          Instead, I just pulled the GFX card from the riser and hung the riser over the side of the chassis, out of the way, making sure the light grey wire (shown towards the right of the above photo) was OK.

          Removing the VRM

          Once the GFX card is out of the way, it’s relatively easy to remove the VRM module (That’s the other riser on the right), opposite the RAM slots.

          Since I had some difficulties removing the GFX card, I removed the VRM first, to give me more space, but the principle is the same.

          There is a little grey catch toward the back of the unit, next to the VRM module.

          • Use a screwdriver to release it by sliding the catch to the left (if oriented as shown below). Note that there is very little feedback from the clip. Just push it back gently while pulling the VRM up and out, vertically.

            fig 6

            Extracting the motherboard

            In order to extract the motherboard, you need to ensure you have done all of the following:

            • Removed the GFX card.
            • Removed the VRM.
            • Unscrewed the two motherboard screws along the front edge of the board as shown in fig 3.
            • Removed the “unique screw” from near the VRM. (fig 7)
            • Removed the “long screw” from near the memory slots. (fig 7)

              fig 7

              • Unscrew the three, spring-loaded screws from around the large grey chip in the middle of the motherboard and pull them out vertically. Mine were quite stiff and required wiggling to get them out.

                fig 8

                Before you can extract the motherboard, it has to be released from the big central heatsink beneath it, which due to heat and time will have fused itself to the CPU’s heatspreader because of the thermal sheet between them.

                I found the method used to separate the two from each other very difficult. Perhaps because my screwdriver was too big. I couldn’t get it between them to start prying them apart.

                • I started from the corner by inserting my screwdriver and twisting gently. The heatsink came away easily enough.

                  fig 9

                  Once you’ve lifted the motherboard away slightly from the big heatsink, pull it towards you, away from the bottom of the case, with all the ports on it and parallel to the central heatsink.

                  Remember, there are two posts guiding the rear of the motherboard. If you lift the motherboard rather than pull it towards you, you risk the motherboard’s supporting corners being snapped.

                  Note that the ports on the bottom of the Cube are pushed through holes in the base. These holes are sealed with a kind of metallic springy foam, probably for shielding.

                  You will have to pull the motherboard away from the base with a little bit of force, since the springy foam may have got quite hard with time.

                  Replacing the CPU and heatsink

                  • Remove the old CPU carefully.
                  • Replace with new CPU.

                    This next part is optional, but I hightly recommend it

                    • Scrape off the old thermal compound from the back of the big black central heatsink.
                    • Apply a thinly spread layer of heatsink compound to the new CPU’s heatspreader.

                      fig 10

                      Install the base fan – DO NOT FORGET. THIS IS NOT OPTIONAL. Running the upgraded Cube without a fan will destroy it!

                      Now follow the instructions and put everything back together.


                      Categories: Mac, mods, Technology Tags: , , ,
                      1. September 12, 2009 at 2:08 am

                        hey nanchatte,

                        when i started to read your story i felt familar.
                        i ordered an PowrForc 744x.5 7447 G4/1.5 Cube with OWC.
                        the package contained the processor and the fan, but nothing else.

                        somehow i had the feeling the vrm cable was missing as i suppose it is not in the cube, so i started to google and ended up at your post.
                        Thx for that!!!

                        what did you do to get it working? did you order that cable or could you swing the install anyhow else.

                        i would be super happy, if you could help me out or let me know, that i totally misunderstood the manual.

                        thx for your time and help

                        br oliver

                        • nanchatte
                          October 8, 2009 at 1:07 pm


                          How did the install go? Did you get it working?
                          The 1.5GHz 7447 does not come with a VRM bypass. Apparently, it uses a similar amount of power under low load to the original 450/500 MHz CPU that was originally installed, with a higher peak load, that is still within spec. It does require the fan to be mounted in the base, however.

                          Because there is no VRM, the install was simple, if not trivial, assuming you have the right sized torx screwdriver set. Follow this post’s instructions to get the gist of the install.

                          It took me about 30 minutes, all told.


                      2. October 8, 2009 at 2:38 pm


                        thx for your reply. i´m in asia right now, but i will check it out once i´m back home in europe.
                        you have been a great help.
                        i was confused with this vrm bypass stuff that was shown in the instruction cd from the supplier.

                        your answer is great! thx again. will let you know how it goes.

                        br from bali.


                      3. December 8, 2009 at 1:03 am

                        back home and i installed the powerlogix finally.
                        it took me a bit longer then you, but was no problem with you post.

                        right now i try to get leopard server on my old boy.
                        the requirements for the os should be fine as the the powerlogix gives more speed then required and the 1,5gb ram should also do the job.

                        do you have any expierence, if an os x 10.5 server works with no problems?
                        installation is running right now. will let you know, if i can swing it.
                        would be so cool to have the cube as a server for the rest of the macs in our office.

                        thx for your help again.

                        br oli

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