eGPU – Connecting an external video card to a notebook (DIY implementation)

Due to constraints like orientation, position of the slots on the expansion board and the size of the video card, and trying to fit everything inside some sort of a case, I chose to use a PCI Express riser.


A couple of things about the PCI Express socket. There are many pins in that socket, and some of them are for transmitting data while others are for providing 12V and 3.3V.

A Nvidia GTX 680 card is power hungry card and it will exceed the max of 25W provided by the original Sonnet Echo bundled 12V power brick adapter. We also need some 3.3V lines to power it. The easiest solution for this is to use an ATX Power Supply because that one can provide both required voltages and also enough power for any highend video card.

The riser extender cable was marked for both sides, required wires were identified and then cut and soldered to an ATX motherboard extender cable in order to be powered from the PSU.






The operation above was also required in order to avoid some issues (PERST# delay) with computer having time to „see” the video card after doing POST initializations by the BIOS. You may ask why the 12V wires were splitted, considering the card could draw the voltages over the dual 8 pins connectors from the ATX PSU. Well, the Sonnet Echo Expansion board was also powered from 12V from the original brick adapter, and allowing current to flow from both ways might not be a clever ideea.

Also, why did I cut the first 3 wires for 12V, when the PCI Express specification labels the third pin as Reserved and only the first two pins are for 12V? The reason is simple, please get a video card and take a look at the pins, you will see that first three pins on side B are connected and like mentioned above you don’t want current coming from ATX PSU to flow back into the Sonnet Echo Expansion board.

After connecting all pieces together, we are ready to power on the whole thing, and it works, at least at the electrical level.

7 comments la: eGPU – Connecting an external video card to a notebook (DIY implementation)

    1. So you left out the most important information, the penalty of thunderbolt/usb3 and the memory buffering. The most important reasons you see few/no such implementations in the wild.

    2. Compared to desktop, yes. Compared to the dGPU in the laptop…you can see the graphs…

    3. Awesome stuff Monstru! Like it 🙂 Now I want to attach this to my MacBook Pro Retina and do some 3k gaming on it 😀

    4. Glad you like it, I hope it helps a lot of users 😀

    5. Great work!!! Would it be possible to run the pcie with a powered riser? The Sonnet Board needs still be powered, right? Possible to power it through PSU? Thanks

    6. Joseph wrote on:

      I don’t know whether or not I should be posting this here, but I’m having a problem with an egpu unit, when ever I attatch it to my laptop and boot up (either with or without the drivers) my laptop screen on boot up goes to a GPU fail screen (multicoloured and pixelated). I’ve yet to find anyone else with the same problem and from my testing I’ve yet to find a solution :'( .

      If anybody could help me solve this problem I would be over the moon 🙂

    7. What a great explanation. Thanks! From the moment I saw the bandwidth of thunderbolt I knew this would be possible and I am sure there is a commercial market for it. Meanwhile, hopefully more and more enclosures come out with boards which can help make this easier still.

      …and sure, it won’t beat a desktop with the same GPU, but it gives you the chance to have an ultra portable with desktop class graphics which is also upgradable! Brilliant!


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