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I have a MacBook Pro (13-inch, 2017, Two Thunderbolt 3 ports) version 10.14.5.

A first monitor (DELL P2719HC) is connected through thunderbolt 3 while a second monitor (DELL E2313H) is connected through a VGA adapter. The latter is the one flickering!

Flickering stops when I disconnect the first monitor. Thus, it's not a problem of the adapter, nor the screen. I am guessing this is due to my laptop not being able to give enough fps to both screens (they both require a 60Hz refresh rate at minimum, which I cannot change event with some command line tools).

I tried to reset VRAM and SMC, but it did not work.

What else can I do?

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This problem is not due to the computer not being able to serve the necessary amount of "fps". Instead this is a hardware problem.

VGA is an analog signal. If the signal is distorted or interfered with, it could problems such as flickering. The flickering stops when you disconnect the first monitor - which indicates that this monitor (and cable) is the source of interference.

I would suggest replacing the VGA cable with one with a ferrite bead instead. Another option is to replace the VGA adapter with a DVI adapter and connect to the monitor using a DVI cable.

If possible you could also try to the cables seperate from each other physically (i.e. get distance between them) - but it is difficult as they need to plug in to the computer very near each other.

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  • Indeed, the problem was a ground loop interference. I simply removed the ground pin from my screen's power supply and the flickering disappeared. It's not the safest solution, but it worked! Sorry for the (very) late accept :)
    – Toool
    Apr 2 '20 at 9:57

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