HDMI Port suddenly stoped recognising external monitor.

Question

HDMI Port suddenly stoped recognising external monitor.

Hi,

I have a 16" 2021 MacBook Pro M1 Max with 32Gb ram running Sonoma 14.5 (23F79) and I have it coupled via an HDMI cable to a 32" Benq EW3270U UHD display/monitor. So a direct HDMI to HDMI connection which has been working fine for over two years. On Friday last week, due to the fine weather I decided to work in the garden so I followed my usual routine when working away from my desk, I closed down of the MBP, disconnected all the cables and headed for the garden. When I'd finished my work I shut down the MBP, came back inside to my desk, connected all the cables again and booted up the MBP. From that point the MBP no longer recognises the external BENQ monitor.

So far, I've:

- Swapped the HDMI cable with one that I know works, still won't recognise the BENQ.
- Proved the BENQ HDMI port is working by connecting up another MBP directly, and it works fine.
- Tried to force the MBP to detect the BENQ by holding down the options key and pressing the "Detect Displays" button in the Settings>Displays menu. No external display detected.
- Shut down the MBP, disconnected all cables, rebooted, plugged in the HDMI cable, Still no external display detected.
- Shut down and rebooted the MBP several times, no external display detected.
- Tried to connect to another HDMI capable monitor, no external display detected.
- Shut down BENQ (removed the power plug) left for several hours, plugged back in and powered back on, no external display detected.
- Connected to the BENQ via USB-C, BENQ immediately detected and working fine.

So from all this I can only assume that the HDMI port in the MBP is faulty, though what made it so I have no idea.

Of course the MBP is now out of support, with seems to be typical these days, although local country Consumer Laws for the UK say that a product should be covered for 6 years, so I may be able to get a free repair, I'll have to check with the Consumer Advice Bureau.

In the meantime, is there anything else I should check or try before heading to the Apple Store to argue about wether I should pay for the HMDI port to be fixed?

Thanks in advance for your advice and guidance.

Howard.

Posted on Jun 24, 2024 10:26 AM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

142,417 points

Jun 28, 2024 7:31 AM in response to howardfromrochdale

I don't see any heading in the hardware section for HDMI, so I think HDMI devices will only be listed under the Graphics&Displays section.

I checked my M1 MacBook Pro 16-in with PRO processor and same story -- there IS an HDMI port, but definitely no separate listing for HDMI when not in use. the Hardware list does not tend to vary. It typically has entries for things that can not pointy exist on a certain Mac. (for example, MacBook Pro has no PCI slots, or parallel SCSI, but there are entries for those.)

From your descriptions, it seems like the only thing that has not been swapped around is the HDMI port on the computer chassis. You could shine a bright light in there and look for obstructions or bent pins.

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Answer 2

Jun 26, 2024 10:31 AM in response to howardfromrochdale

now that you know what it is doing when working correctly, ask your Mac if it 'sees' the display, regardless of whether it is willing to put up a coherent picture on the display:

 menu >about this Mac > (system report) > Graphics&Displays

...

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Answer 3

Jun 24, 2024 10:32 AM in response to howardfromrochdale

recent versions of MacOS have improved ability to detect errors, and REJECT cables that provide ANY errors at the requested resolution and effective data rates. You likely need an better cable.

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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Answer 4

Jun 25, 2024 6:33 AM in response to howardfromrochdale

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)

so try doing some of those things and see if the display comes alive.

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Answer 5

Jun 27, 2024 8:41 AM in response to howardfromrochdale

<< nothing detected >>

identification of a display using the communication over the secondary data channel, which goes by various names including EDID data channel, is it very slow speed and is really, really easy to have working perfectly.

Your display is a modern display that should support that feature (and does, over a different input medium)

Here are two possible issue that come to my mind:

• your display cable does not support the EDID data channel or has a broken wire there. Since this uses different conductors than thee main data conductors, that cable would still work great with non-Mac devices.

• Your high-end display is busy paying rapt attention to its Thunderbolt channel, and is simply NOT LISTENING to the EDID data from the HDMI channel. Another way of saying that is the display is SET to Thunderbolt input, to the exclusion of all others.

The way to investigate and fix is to use the "on-screen" display functions inside the display itself, and check that all ports are equally available for connection at any time.

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Answer 6

Jun 25, 2024 2:05 AM in response to Grant Bennet-Alder

Hi Grant,

All the cables I use are top quality certified, and have the hologram label, they have been purchased from Richer Sounds as I have a quality AV set up for my LG UHD TVs in the house. I'm not sure how that would explain the scenario where it works and then after a shutdown and disconnect then an attach and reboot a few hours later when it doesn't work, unless the cable was damaged in some way. That's why I swapped the original premium cable with another known to be working premium cable which gave the same result. The original cable is working fine in my AV set up for one of the LG UHD TVs. I would have thought that if it was a Mac OS issue then it would have made itself apparent at the last upgrade which was several months ago and the MBP has had numerous reboots over that period.

To be certain I've taken a brand new premium certified cable and swapped out the replacement cable so that I now have a brand new cable in place but I still have the issue where the monitor is not being detected.

Thanks for the advice and information but I'm 100% certain it's not a cable issue.

p.s. I've just found a support article on how to run diagnostics on apple silicon, so that is next on the list of things to try.

Thanks again and best regards Grant,

Howard.

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Answer 7

Jun 28, 2024 7:15 AM in response to Grant Bennet-Alder

Hi Grant,

so checked all the settings an it's configured to auto select when a device attempts to connect to any of the ports. I've changed that setting so that it only looks for the HDMI port, but still nothing detected on the Mac. As I've already proven the cable to be working to spec by attaching another MBP (a friend of mine has exactly the same model as me running the same OS version and puild) and this works fine with the Benq external display using the direct HMDI to HDMI connection I think a fault cable has been categorically ruled out. Just to to try and narrow the issue down even further to the MBP port I plugged in a cable that has a Thunderbolt male connector to HDMI male connector and that works fine so its definitely not the Benq that is at fault. This was tested with the Benq set to only allow HDMI connections and. to allow the Benq to auto select when it detects a signal.

Here is a question..... Should the system report show or mention HDMI anywhere even when the HMDI port is not in use? As the moment I can't see anything anywhere in the report even if an HDMI cable is connected to the port and connected to any of there HMDI capable monitors I have.

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Answer 8

Jul 1, 2024 7:58 AM in response to Grant Bennet-Alder

Hi Grant,

Yep..... well there is definitely something in there but weirdly I've checked the cable and plug itself and there is nothing missing. all the pins are present.

I'm wondering now if someone has tried plugging something else into that socket which has left some sort of pin behind.

I've got some very small wrist watch tweezers, so I'll see if I can gently remove it next time I power down.

I'll let you know how I get on.

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Answer 9

Jun 26, 2024 10:03 AM in response to Grant Bennet-Alder

Hi Grant,

Yep, done all those, but still no signal and no display detected in the system>displays section on the MBP.

😞

Kind regards,

Howard.

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Answer 10

Jun 27, 2024 2:31 AM in response to Grant Bennet-Alder

Hi Grant,

nothing detected when using the HDMI port. Of course the screen is detected immediately when I use a a thunderbolt cable.

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HDMI Port suddenly stoped recognising external monitor.

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