Vertical Line Issue on external Monitor with M4 MacBook Pro

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Level 1

4 points

Vertical Line Issue on external Monitor with M4 MacBook Pro

I recently got an M4 MacBook Pro and connected it to my LG UltraGear 4K 144Hz monitor using a brand-new HDMI 2.1 cable. However, I’m experiencing a strange issue where vertical separations (single or double lines) appear on the screen. You can clearly see the effect when moving the mouse. Here's a video showing the issue: Video of the issue

Some key observations:

The issue doesn’t always happen, but when it does, I’m not sure how to get rid of it.
I have a second HDMI cable connected to another port, and switching cables makes the issue disappear temporarily, but it eventually returns.
Initially, I suspected the 120Hz refresh rate was causing it, so I reduced it to 60Hz—the issue disappeared the first time.
However, when I switched back to 120Hz, the issue returned after some time, and lowering the refresh rate to 60Hz again didn’t fix it.
I haven’t been able to identify a clear pattern for when it happens or how to resolve it.

Has anyone else experienced this? Could this be a macOS compatibility issue, an HDMI 2.1 problem, or a monitor setting? Any advice on troubleshooting this further?

MacBook Pro 14″, macOS 15.3

Posted on Mar 6, 2025 9:38 AM

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Answer 1

a brody

Level 10

85,320 points

Mar 8, 2025 8:00 AM in response to sadiromer

Based on that information, I can only say there is something wrong with the graphics chip signal of the MacBook Pro. I would bring the monitor and MacBook into an authorized repair center and share what you did here. You did exactly the sort of troubleshooting I would have. Backup your data before you bring it in as they may want to mail it in. You can also call AppleCare and ask them to send you a box to send it into repair. Sometimes that is faster. Get a case number either way so you can follow its progress.

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Answer 2

a brody

Level 10

85,320 points

Mar 6, 2025 6:05 PM in response to sadiromer

Vertical lines such as these usually are indicative of an inverter cable or board issue. I would certainly check which HDMI version your monitor is compatible with and use at least that version. Verify your monitor fully supports 120 Hz at that resolution with the manufacturer and that HDMI version does too.

GIven two cables, and two separate ports have the issue, suggests that the problem is within the monitor circuit board, if you are using the correct version and the monitor supports that Herz. Reach out to the monitor manufacturer to see if they can look at its inverter assembly.

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Answer 3

sadiromer Author

Level 1

4 points

Mar 6, 2025 6:37 PM in response to a brody

This monitor has two HDMI 2.1 ports. I have my PS5 connected to port 2 and a Windows laptop running at 4K 120Hz on port 1. I’ve tested with a brand-new HDMI 2.1 cable as well as two older ones, and the issue persists regardless of the cable used. This confirms that the problem is not with the monitor or the cable.

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