External Monitor suddenly wrongly recognized

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Level 1

4 points

External Monitor suddenly wrongly recognized

I have a Macbook Pro M1 Max and an LG UltraWide monitor 29UC88 plugged through HDMI and used as a main display. This has been my setup since I've got the laptop like 3 years ago.

This morning I worked a bit at home everything was file. Unplugged everything, worked a bit from the office where I plugged in through USB-C another terminal (wasn't the first time) and then went back home. I would say I do this once a week without problem, until today.

When I plugged back my HDMI cable, the external monitor was super scaled. Went into `System Settings > Displays > <External Monitor>` and resolution was at `1280 x 720 (Default)` and the only other option is `1920 x 1080`.

For an unknown reason, the monitor capabilities does not seem to be recognized correctly anymore and the OS doesn't let me force a resolution of 2560x1080 which is the native resolution of the LG monitor I have.

Nothing changed between this morning and when I head back to home regarding configuration nor OS updates.

I tried:

Different HDMI cables
Unplug/replug with very long delays (multiple minutes)
Reboot
Shutdown
Updated to Sequoia 15.0.1
BetterDisplay app
`Detect Displays` in System Settings

It seems the monitor is not recognized correctly anymore. The monitor seems to be recognized with `"ManufacturerID"="00-00-00"` and `"ProductID"=0`:

```

$ ioreg -l | grep "DisplayAttributes"

| | | | "DisplayAttributes" = {"TiledDisplayInfo"={},"ProductAttributes"={"ManufacturerID"="00-10-fa","ProductID"=53000704963649,"LegacyManufacturerID"=1552},"DisplayAllocation"={"ExtraPipes"=0,"MainUFP"=0,"UseSingleTile"=No,"PeerUFP"=0}}

| | | | "DisplayAttributes" = {"PortID"=48,"MaximumVariableRefreshRate"=0,"MinimumVariableRefreshRate"=0,"ProductAttributes"={"ProductID"=0,"ManufacturerID"="00-00-00","LegacyManufacturerID"=0}}

```

Also, EDID retrieval through BetterDisplay didn't work, which points also in the some problem identifying correctly the monitor.

Any idea of what happened and how I can fix it? Anyways to force OSX to use a specific resolution of 2560x1080?

Regards,

matt

MacBook Pro 16″, macOS 15.0

Posted on Oct 17, 2024 6:41 PM

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Answer 1

maoueh Author

Level 1

4 points

Oct 18, 2024 8:11 AM in response to maoueh

The monitor has a DisplayPort. So I just bought a DisplayPort to USB-C cable and connected in the monitor, monitor capabilities are recognized correctly again and the resolution is now correct.

I still have no idea(s) about what happened exactly and why through HDMI it's not working anymore. I'll perform more tests as I'm really curious to see if the HDMI port/connection is broken. I'll try a third HDMI cable and also I'll try to connect it to other external monitors I have here through HDMI to see how it looks like.

New `ioreg` now with DisplayPort -> USB-C:

$ ioreg -l | grep "DisplayAttributes"
    | |   |   |   "DisplayAttributes" = {"SupportsSuspend"=No,"MaximumRefreshRate"=75,"SupportsActiveOff"=Yes,"PortID"=32,"ProductAttributes"={"YearOfManufacture"=2017,"ManufacturerID"="GSM","SerialNumber"=122321,"ProductName"="LG ULTRAWIDE","LegacyManufacturerID"=7789,"ProductID"=23026,"WeekOfManufacture"=10},"MaxVerticalImageSize"=34,"MinimumVariableRefreshRate"=3670016,"MaxHorizontalImageSize"=80,"HasHDMILegacyEDID"=No,"Chromaticity"={"Red"={"X"=42688,"Y"=21760},"Green"={"X"=20096,"Y"=41344},"Blue"={"X"=9856,"Y"=3904}},"DefaultColorSpaceIsSRGB"=Yes,"NativeFormatHorizontalPixels"=2560,"DefaultWhitePoint"={"X"=20544,"Y"=21568,"Gamma"=144179},"SupportsVariableRefreshRate"=No,"AspectRatio"=17,"MinimumRefreshRate"=56,"MaximumVariableRefreshRate"=4915200,"WhitePoints"=({"X"=20544,"Y"=21568,"Gamma"=144179}),"PreciseAspectRatio"=154202,"ContinuousFrequencySupport"="None","SupportsStandby"=No,"NativeFormatVerticalPixels"=1080}

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Answer 2

maoueh Author

Level 1

4 points

Oct 29, 2024 9:07 AM in response to maoueh

So, here my latest update.

After getting a workaround with DisplayPort -> USB-C, I tried back my HDMI port with another older LG monitor I had and it didn't work with this monitor either over HDMI. The monitor was not recognized correctly.

Then a few days later, went back to the office and plugged back my work's monitor in laptop, DP -> USB-C there too. That worked. Then tested the HDMI from monitor to HDMI to my macbook. That worked too, the monitor was correctly recognized.

Went back home then re-tested my "broken" monitor. Now everything was recognized again, HDMI port works, monitor is detected correctly. EDID can be retrieved. Back to normal.

So the hypothesis that the HDMI port is broken is incorrect.

What I think happened is that something got "cache/broken" when I plugged my work's monitor and it persisted at least 48-72 hours. I have the impression that connecting back my work's monitor make everything work back, but it's not 100% certain, I would have need to test on the morning my "broken" monitor over HDMI, go to the office and test it back at home.

Anyway, if it can help anyone reading this!

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Answer 3

Oct 29, 2024 10:18 AM in response to maoueh

it sounds like you know this, but I will add it for readers who may not:

The Mac does not rely on windows-like side-loaded "Drivers" which are actually packages of resolutions and settings for a specific display. Instead, it goes straight to the immutable source -- it asks the display itself.

To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• hold the Option key while you click on the (Detect Display) button that will appear in Displays preferences (from another display)

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Answer 4

Oct 29, 2024 10:20 AM in response to Grant Bennet-Alder

switching to a different HDMI cable is a check against broken wires. Bu if both cables were working, a different cable may not improve the situation.

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" --OR--

"Ultra High Speed HDMI cable" or that + "48G"

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

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External Monitor suddenly wrongly recognized

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