2 new Macbook pro M4s, multiple new HDMI cables, and HDMI out still doesn't work

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Level 1

12 points

2 new Macbook pro M4s, multiple new HDMI cables, and HDMI out still doesn't work

Hoping the community can help me. I'm on my 2nd new macbook pro with the HDMI out not working. First one I went through the full gamut of apple diagnostic support after googling and troubleshooting (standard stuff - deleting local files, checking HDMI cables, etc). Apple support pushed me over to the genius bar at an apple store, they told me to return/replace it. Onto my 2nd, same exact issue.

My monitor is nothing outrageous - its a 24" LG 24U631A-B.

For the record - the monitor and the HDMI cables all work perfectly with my Macbook Pro M3. But neither the 14" or 16" M4 HDMI out has worked with this same setup. The same HDMI cables work when I use my USBC to HDMI adapter on the M4. But direct connect from HDMI out to monitor does not work on any HDMI cable. On both new M4s.

I'm at a loss as to what the issue could be. Obviously Apple is unable to troubleshoot any further than they have. Hoping the community has any pearls of wisdom that may help me get to the bottom of this.

Only thing I can think of is it could be something related to my M3 files that I use migration assistant to transfer to my first and then second M4. But part of the troubleshooting process is removing saved display files, which I did. So I'm not sure what else this could be.

MacBook Pro 16″

Posted on Nov 4, 2025 9:14 PM

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Answer 1

Nov 5, 2025 12:58 AM in response to rh5259

rh5259 wrote:

My monitor is nothing outrageous - its a 24" LG 24U631A-B.

LG – 23.8” QHD IPS Monitor with USB-C (24U631A-B)

This is a 23.8" monitor with a resolution of 2560x1440 pixels, and a refresh rate of 100 Hz. It has a HDMI input and a USB-C (DisplayPort) one. The manual says that both support 2560x1440 at 59.951 and 99.946 Hz.

The monitor's menu includes an "Input Compatibility Version" setting.

For HDMI, the choices are v1.4 and v2.0
For USB-C (DisplayPort), the choices are v1.2 and v1.4

You haven't told us which M4-series chips are in your 14" and 16" MBPs, but I believe that

14" MBPs with plain M4 chips support DisplayPort v1.4.
14" and 16" MBPs with M4 Pro and M4 Max chips support DisplayPort v2.1.
All of these MBPs support HDMI v2.1. ("One external display supported at 8K resolution at 60Hz or one external display at 4K resolution at 240Hz over HDMI" isn't consistent with the limitations of HDMI v2.0 and earlier.)

Generally speaking, a computer running a higher version of HDMI or DisplayPort can connect to a monitor that only supports a lower version in a "lowest common denominator" fashion.

MacBook Pro (14-inch, M4, 2024) - Tech Specs - Apple Support

MacBook Pro (14-inch, M4 Pro or M4 Max, 2024) - Tech Specs - Apple Support

MacBook Pro (16-inch, 2024) - Tech Specs - Apple Support

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Answer 2

Nov 5, 2025 8:46 AM in response to rh5259

Changing to a different HDMI cable is a check against BROKEN cables. It does nothing for cables that are not high enough spec.

HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:

"PREMIUM High Speed HDMI cable" or that + "with Ethernet" (up to 4K at 30Hz) --OR--

“ULTRA High Speed HDMI cable" or that + "48G" (supports higher resolutions and backward-compatible)

Cables with No Certification tags are good for your standard 720p TV set, and not much more.

HDMI was invented for HD TV sets. it works great at its original resolution of 720i or 720p. At higher resolutions, it quickly develops issues that are complex to solve, and the cables and adapters required to solve are NOT intuitive.

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Answer 3

rh5259 Author

Level 1

12 points

Nov 5, 2025 5:51 AM in response to Servant of Cats

Both laptops are M4 Pros 14/20 configuration, both brand new. The V1.4 / 2.0 toggle on the monitor did not result in any difference in outcome. The macbook does not recognize the external monitor. The HDMI out works as I have a separate portable external monitor and it works just fine with that, so it must be specific to the monitor. But I have no idea why.

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