Monday, February 15, 2021

Power Mac G4 Cube - Power Supply replacement


The Power Mac G4 Cube is a very unique Apple computer, with its special and compact desktop (for the time at least) "cube" form factor. It features  easy access to its internal components for (some) upgrades, but mostly, this accessibility is used to show off to your friends and family. 
Unfortunately, it ended up being a commercial failure due to lack of specific market focus and higher price compared to other Apple products of its time with similar or higher specs. Thus, it had a very short life span, being produced only between July 2000 and July 2001 what today lead to a somewhat rare and collectible Mac.


The Cube, like most Apple products, is a solid machine and if you are lucky enough to find a reasonably priced one, most units tend to be working to this day. Among the non-working ones available, chances are that it's because of its power supply (PSU) being dead. Sadly, the Cube PSU is custom made for the Cube, using a proprietary connector cable - making it very rare / expensive to find a plug and play replacement. 

Thankfully, you are lucky enough to come across this article! :)





If you have a Cube with a dead PSU, you can use this tutorial to replace it by a modern PSU preserving the original cable, power connector and overall OEM case of the original Apple made PSU.

First, you will need to open the OEM PSU to remove (unsolder) the original cable and power connector plate. I used this guide (from iFixit user Darie H.) to open the OEM Apple PSU. Be patient as it is not easy to get to internals of the original PSU.

Once you open the original PSU, you will be able to desolder both side plates: one with the connector and one with the power plug:



With the original cable in hands, connect it to a bench PSU adjusted to 28V DC to test the Cube and ensure it works. Here is the pinout for the power cable: (A and B are +28VDC, C and D are the negative of the +28VDC and the outer shell is ground):




Testing the Cube using the original power cable connected to a bench power supply adjusted for 28V DC:



Note that in my test above, the Cube is also powering the Apple Studio Display through the ADC connector. I wanted to check the current drawn with the display connected and without to order an appropriate 28VDC power supply.


The original Power Supply has 205W, meaning it can provide a current up to 7.3A. In my tests with the 15" Apple Studio Display connected it never drawn more than 2.5A. Nevertheless, I wanted to replace with the closest capacity I could find. 28VDC power supply are not really common, especially with high wattage, but I was able to find one (very) reasonably priced at AliExpress:



Link to the power supply I found: https://www.aliexpress.com/item/32831209276.html


The dimensions of this power supply are slightly smaller than the OEM, so I gave it a go! Several weeks later, the power supply arrives from China so I put it to test. Bingo! It works as it should!




Unfortunately, despite the new power supply fitting perfectly inside the original PSU casing in terms of height, it is about 1.5" too long to allow the original side panels to be used. That is a bummer!



 
I cannot fit the new PSU inside the OEM case and keep the original OEM panels on the side as I intended. As even if I remove the new PSU from its metal casing, it still won't fit, now I need to decide between giving up using the OEM side panels or the OEM case altogether. 


But wait! What if I could design and 3D print an extension to the original PSU casing?




It was an easy design and an easy print. I got it to fit perfectly on the first try, with the help of some gorilla tape (taped from inside) keeping the extension and original casing together. You can download my design above for free from here:


I just soldered some extension wire to the original leads wire as the input and output connectors on the new PSU are on the same side (instead of opposite sides on the OEM PSU):



I then used double sided tape to glue the new PSU metal casing to the original plastic OEM case:



Even though the fit was tight on both side panels, I used a little bit of hot glue to keep them in place: 



Note the green led light inside showing that the power is on

 
And everything is up and running!




I'm quite happy with the results in terms of functionality and aesthetics :)




Thanks for checking it out and good luck with your repair!


7 comments:

  1. Somewhat unrelated question - what's up with the white supports in the corners inside the clear case?

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  2. The white supports are actually supporting the heavy Cube on the table instead of stressing the fragile policarbonate. These supports should help to prevent the typical hairline cracks on the Cube's acrylic case. Here is a link for these supports: https://www.thingiverse.com/thing:2297009

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  6. Nice work! Im thinking about doing something like this cause im running my g4 cube as a nas 24/7 (with 2 ssds in it). The original power supply is terrible (in terms of efficiency) so thats why it would be well worthed for me to do this.

    Also this project is kinda scarry. (Its not so much about doing someting wrong its more like that I dont really want to leave the house leaving something like that pluged into my wall unattended)

    "making it very rare / expensive to find a plug and play replacement"
    So you found plug and play replacments? :) Would you be able to link them please <3
    This is what I found after researching the entire internet: (power supply)

    https://www.pc-adapters.com/28v-switching-power-supply/55244955.html

    It has perfect wattage etc.
    Together with this adapter:

    https://www.mouser.at/ProductDetail/MEAN-WELL/DC-PLUG-P1J-R7B/?qs=rI7uf1IzohRATPfbfB5rhQ==

    IDK if it would work though! (Dont know if the adapter would do the right job)

    I would really appreciate if you could please let me know what you think about it.

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    Replies
    1. Hello memorian, what I meant when I said "plug and play replacement" was buying a used or NOS original OEM Apple PSU adapter for the Cube (on ebay for example). They show up from time to time, but it is going to be costly and no guarantees on how long they would last.

      The 28V DC power supply you recommended should work. As for the plug you linked, I don't think this is the right plug. From what I researched, the Cube power plug is called PDP-40, where the pair of positive pins have bigger diameter than the negative pins. You can find the plug spec here: https://www.cuidevices.com/product/resource/pdp-40.pdf

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