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MBP '15 unusably slow after being connected to external display via HDMI

I have a mid 2015 MacBook Pro running Mojave that can't seem to handle being plugged into an external monitor via HDMI. It runs fine for about an hour, then starts lagging to the point where it's very difficult to get anything done! I'm at a loss, being hunting around the internet for solutions and have tried several things to no avail.


Resetting PRAM didn't help.

Switching HDMI cables didn't help.

Running things like Onyx and CleanMyMac haven't solved the problem.

I try closing most programs and running only a few spaces, but even just having a browser open with the external display connected seems to be asking too much!


Of course, as soon as I disconnect the external display the MBP runs perfectly fine.


I'd be so grateful to hear if anyone's had a similar experience and what they did to solve the problem. I'd love to be able to use this machine with an external display as that seems to be well within its capabilities.


Thank you!

MacBook Pro Retina

Posted on Sep 21, 2019 1:46 PM

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Question marked as Top-ranking reply

Posted on Sep 23, 2019 2:53 PM

Hello thedodus,


Thanks for using the Apple Support Communities!


I see from your post that your MacBook Pro begins to perform slowly when it's connected to an external display via HDMI.


Try resettings your Mac's System Management Controller (SMC) by following the steps in this Apple Support article:


How to reset the System Management Controller (SMC) on your Mac


I hope this information helps!


Cheers.

Similar questions

3 replies
Question marked as Top-ranking reply

Sep 23, 2019 2:53 PM in response to thedodus

Hello thedodus,


Thanks for using the Apple Support Communities!


I see from your post that your MacBook Pro begins to perform slowly when it's connected to an external display via HDMI.


Try resettings your Mac's System Management Controller (SMC) by following the steps in this Apple Support article:


How to reset the System Management Controller (SMC) on your Mac


I hope this information helps!


Cheers.

MBP '15 unusably slow after being connected to external display via HDMI

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