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Black screen/monitor disconnection on Catalina 10.15.4.

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Nov 23, 2011
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Motherboard
Gigabyte Z370M-DS3H
CPU
i5-8400
Graphics
UHD 630
Mobile Phone
  1. iOS
Hi. This is not really a help thread for my specific build, as the bug I'm going to describe is currently affecting many different builds, even real Macs from what I can read on Apple's forums. Actually, I'm quite surprised this isn't being widely discussed. The aforementioned bug works as following: the boot process starts, more than half the bar loads, the screen quickly refreshes (that's the expected behaviour on my build, anyway), the Apple logo reappears and then, a fraction of second after loading the login screen (which you can manage to glimpse), the screen goes black. At this point, were you to connect an HDMI cable, Mac would simply recognise that monitor/TV as your main screen.

A couple notes on the matter. First of all, this bug is not so much a post-installation one as a general issue with the 10.15.4 update. That is, even the installer disconnects your monitor during the whole update process: in fact, I had first thought it was stuck but Mac was actually working (which is the reason why I switched to OpenCore but... it's another matter entirely). Catalina 10.15.3, on the contrary, works flawlessly (in my case, everything has been properly configured, I'd say it's a perfect hackintosh). Now secondly, if you're using a DVI monitor, disconnecting the DVI cable and reconnecting it temporarily solves the issue. Moreover, HDMI doesn't seem to be affected by the bug, as long as you let Mac boot first.

All this leads me to think: what on earth changed, graphics-wise, in Catalina's latest release? Am I missing something obvious or a major thread? If you add all this to Catalina's alleged crashes and KP... the 10.14.5 update will probably be released soon enough.

Quick update: adding the boot flag igfxonln=1 solves the issue, but why so?
 
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This worked for me as well. Previously on Mojave my external monitor was working perfectly but with internal display only my laptop would no longer boot (it would hang halfway on the apple logo and fans would spin up) I think that was due to a recent security update for Mojave. Anyway with Catalina my external monitor would go black at login screen but the issue is fixed with igfxonln=1 and the internal monitor works perfectly in Catalina (no hang at boot).
 
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