[HELP] eGPU monitor support in pre-boot
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[HELP] eGPU monitor support in pre-boot  


New Member
Joined: 4 months ago



I sucessfully built an eGPU with a Sonnet 650 and Vega64, cramming everything in there including a custom water loop :). All in all the setup works great. However, I (need) want to use Bootcamp windows which I have installed on external SSD. I boot using the option key and selecting the drive, security is set to low and this works without the egpu.

However, when using the eGPU and the monitor connected to the GPU directly, I can't seem to get any "image" in pre-boot mode. My GPU and monitor turn on, the desktop stays black. This happens when trying to use recovery mode (cmd+r) or boot options (option). Waiting does not help. When using no modifier, the mac starts as usual. Any ideas?


* I can't star into macOS and then select my external as boot volume to skip the pre-boot selection since the external drive wont show up...

Mac mini 2018, 32gb RAM, macOS 10.15, Sonnet 650, Vega65, Watercooling

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Mini i5
Honorable Member
Joined: 1 year ago


Yep, Apple disabled that functionality in their Mac mini firmware updates for Catalina 10.15.2 - 10.15.5 (and also Mojave 10.14.6)

A couple members have reported it is restored by the firmware update included with the Big Sur developer beta.

If we are lucky, Apple will include a firmware fix for the Mini in the Big Sur public beta and official releases. 



2018 Mac Mini i5 / 6-core 3.0-4.1 Ghz / 32GB / 256GB / Intel UHD 630 / PowerColor Gaming Station / PowerColor dual-fan RX 5700 XT / Mac OS 10.15.6 Catalina / Windows 2004 😏 / Dual LG 27" 4K displays

Active Member
Joined: 1 year ago

@max3-2, while waiting for apple to fix the firmware, You can do these trick. 

1. Plug hdmi cable from mac mini to monitor and displayport cable from egpu to monitor. I suggest don't use hdmi port on mac mini to avoid error 12 on windows, use usb c to hdmi converter instead. 

2. Set monitor input to hdmi, then start the computer with holding the option button. You should be able to see boot drive selection screen.

3. Choose windows, then wait until windows logo appear and then switch your input monitor to displayport. You may need to disable the 2nd display  on windows display setting. 




This post was modified 3 months ago

2018 mac mini i5 + sonnet 550 + vega 56

2018 Mac Mini [8th,6C,B] + RX Vega 56 @ 32Gbps-TB3 (Sonnet Breakaway 550) + macOS 10.14 & Win10 [build link]