2.2 GHz (Turbo Boost up to 3.4 GHz), 2.5 GHz (Turbo Boost up to 3.7 GHz), or 2.8 GHz (Turbo Boost up to 4.0 GHz) quad-core Intel Core i7 processor with 6 MB shared L3 cache.

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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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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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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.


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


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


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?


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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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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