Mirroring via HDMI issues

[El_Capitan]

Hi everyone,

I’m running a High Sierra with the latest updates on my mid 2011 MacBook Pro. Generally I use this machine with the external HDMI monitor and keep my laptop closed. I have an external wireless keyboard and a mouse connected to it as well. This setup was running beautifully for years until the last update to High Sierra!

Now, it simply won’t push any signal through the HDMI. It does work through a VGA adapter which is weird. Adapter is fine, cables and connections are fine as well. Sometimes I get some signal through after a restart or PRAM reset but as soon as I close the lid of my MacBook the signal is lost and even the internal screen goes black.

What have they broken with this update and is there a way to fix it?

Connecting through the VGA works but that’s not a solution to this issue for several reasons.

 

[Brian33]

I think it's possible that the discrete AMD graphics processor might have failed. Granted, this would be a pure coincidence to happen along with your update, but things like that happen. The 2011 MacBook Pros are notorious for this failure. (I have a 15" Early 2011 MacBook Pro.)

To troubleshoot, I would disconnect the external monitor and try to verify that the AMD GPU still works OK with the built-in screen. I'm not sure how to do this, though -- mine failed in pretty obvious ways just using Firefox to browse the web, etc. If you *never* get graphics anomalies with the built-in screen, no matter how graphics-intensive, then I guess you can throw out my hypothesis. However, I have read that the AMD GPU *is* enabled when an external monitor is used -- that's why I suggest this possibility. Also, IMHO you are almost certain to have the GPU fail sooner of later, if you use that Mac long enough. (There is hope, though -- it's possible to force the system to use only the Intel integrated graphics and ignore the AMD GPU, giving you a still-useful system.)

Hopefully my guess is wrong and something else is the matter...