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Computer slows down when connected to external monitors

I am working on a MacBook Pro that has dual GPUS (Intel Iris & AMD Radeon)

The user uses 2 external monitors.

His computer starts slowing down, the kernel usage gets to 87% and oddly bounces as high as 240 %. The laptop is a bit warmer than usual but no thermal problems. The user reports that when this problem started that it was about 1 hour or so before the computer slows down; it is now starting to slow down in about 5 minutes.

The user has reset the PRAM and also SMC reset but no change.

Is this a hardware failure? Thanks

Answered! View the answer I have this problem too

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Having experienced this issue myself using a MBP with 2 x LG LED 24EN43 monitors; I read these comments with interest. Although not mentioned, I just unplugged the monitors and went to System Preferences/Displays/Colour then hit the Calibrate button. That was a perfect fix. Everything works like brand new! Hope this helps you too.

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Sorry mate, I don't see how color calibration (which is just a software profile) would affect the CPU performance, especially when I (I don't know about the others) am experiencing this issue even on boot camp in Windows! Regardless, I tried your suggestion, and it made absolutely no difference; after 30 seconds the laptop was throttling again.

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Seems like the gpu just cant handle the extra horsepower needed to run the monitors. Try it with no monitors and see how long it lasts without them.

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This set up has been running for about a year without problem. This just started recently.

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Try that. There might be issues with the GPU as it seems to be with almost EVERY SINGLE macbook ever made

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It does work better using just the MBP display. Is this a hardware failure of the GPU or is it something else?

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Could be hardware failure of the GPU. Like i said try it with no monitors at all and see how long it lasts. Does the same thing happen with no monitors as fast as it did before?

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This model has 2 graphics adapters. It looks like the Intel iris is used for the display and the Radeon is used for external. It does run longer with out the external monitors connected.

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I would start off by opening the system and cleaning the dust out of the fans. Make sure both working.

I would also download this app: TG Pro even using the free version might clue you in on whats happening with the heat transfer from the CPU and/or GPU. The full version offers more for less than $20 US its worth it!

Look to see if the heatsink temp is following the GPU/CPU's temp. If not the heatsink has likely lost its coolant so the CPU or GPU is not able to shed its heat so the system is throttling down.

If the values are the same then you'll need to look deeper into the system as well as see if the drive is too full. SSD's need a bit of wiggle room for wear-evening. In addition, if the system is only a 8 GB model the system maybe using the SSD for virtual RAM and depending on the app cache or paging.

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I have the exact same problem. However, although this answer has been marked as being the solution, I don't really get what the actual solution is? Because of this phenomenon, I had my logic board replaced 4 times, and also the heat paste has been changed. But still the problem remains, even if only one external monitor is attached to the MacBook.

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The answer is more of a process than > Bang replace this! Type of answer. So did you follow the process? If you did post your outputs so we can see it to get to the next step.

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Have you checked if the display settings are using the external monitors? If it is thats probably it. I changed it back to display and it stopped lagging

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Hey, could you elaborate more on this? This seems to be happening to me.

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I'm having the same problem. I'm using a 2017 MacBook Pro 15" at 3.1Ghz connected to the LG 5K monitor. When connected to the monitor and running a long demanding process (like premiere pro encoding for example), after a minute or so it will throttle down to 1Ghz. My finding is that it power throttles - not thermal. In fact when connected to the screen the temperatures go down to 60C instead of what seems to be the normal limit on the macbook - 98C, but instead of 40W, it is only able to maintain up to 10-15W. It does seem to be ambient temperature-related as it's more affected when it's hotter outside, but none of the internal components are running hot. Apple suggested I reinstall the operating system and test, but I went even further, I tested even on boot camp with windows 10 and had exactly the same behavior, so it's not operating system related.

Did you find any solution yourself? I'm afraid to leave it to apple, as I fear it's more a design problem rather than specific to my case, and they'll end up messing with the logic board without really fixing anything.

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Sounds pretty much the same as my problem. Although the temperature shown in Intel PowerGadget is quite normal, the MacBook Pro 2015 clocks down to 0.8Ghz if an external monitor is attached to it. If I use a Thunderbolt dock, the problem happens sooner than if I attach the monitor via a VGA adapter. Sometimes, it helps a bit if I close the lid of the MBP to disable the internal display, sometimes it does not help.

I never found a solution, even re-installing macOS and changing the LogicBoards 4x (!) did not help. It seems as if this is a design issue which Apple does not want to admit.

BTW: Just yesterday I read that the brand-new MBP 2018 has the same problem. Here Apple admitted the problem, and informed the users that it was due to a missing digital certificate. There's a patch, but only for these devices. Since this info, I am wondering if this is also the root cause for my problems on the MBP 2015. Apple's quality and customer service sucks completely, IMHO.

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Can you adjust screen resolution se if that helps?

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I don't think it's relevant. The problem seems to be that when MacBooks are connected to an external screen via thunderbolt, there is not enough power going through to the processor, hence forcing it to slow down.

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I'm having the same issue with just a HDMI cable plugged directly into the MBP (early 2013), so not related to Thunderbolt on my system.

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It even happens with a VGA adapter.

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