Macbook Pro stopped displaying to external monitor after using USB-C hub with a new PC

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Macbook Pro stopped displaying to external monitor after using USB-C hub with a new PC

I've got a MBP (2018) plugged into a USB-C hub. The hub uses a HDMI->DVI cable to connect to my (admittedly old) monitor. I often unplug the MBP from the hub and plug-in my work PC (and vice versa). This has worked without problems for years.

But my company issued me a new PC (HP Zbook) and all of a sudden my MBP will not display to the external monitor. The MPB does see the monitor, it just won't display anything. I've tried changing resolutions etc. but to no avail. I also tried things suggested in past posts, such as updating the OS and plugging out/in the power cable to the hub. That last act will sometimes temporarily work, but once I switch to my PC and back to my MBP it stops working. I know the cable and monitor are fine since the PC has no issues displaying to the monitor.

I'm at a loss as nothing on my MBP has changed, yet it is the one having the problem. I was going to get a new monitor soon anyways, but I don't want to buy one and then have the same problem.

MacBook Pro 13″, macOS 14.5

Posted on Jun 29, 2024 7:53 AM

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Answer 1

Jun 29, 2024 8:17 AM in response to giants450

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 2

Jun 30, 2024 7:31 AM in response to giants450

what happens is you select a FAR lower resolution?

more recent MacOS will turn off the display if it shows transmission errors.

<< USB-C hub. The hub uses a HDMI->DVI cable. >>

Cable length and standards:

The cable length for the USB-C cable to the Dock/Hub (if not a captive lead-in cable) needs to be ONE meter or shorter.

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 3

Jun 30, 2024 8:23 AM in response to giants450

every time you reconnect to the Mac, your Mac will evaluate the quality of the connection at the current data rate (roughly equivalent to resolution).

If the display can be used at a FAR lower resolution, that suggests cables are not adequate for the task at hand.

What display is this, and what resolution are you asking for?

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Answer 4

giants450 Author

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8 points

Jun 30, 2024 8:21 AM in response to giants450

So I just tried an older USB-C hub that I have, and NOW the monitor works. I'm not sure what's going on with my current one where it will work for the PC but not my MBP.

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Answer 5

Jun 30, 2024 10:07 AM in response to giants450

that appears to be a 1920 by 1080 display with VGA, DVI-D (single-link) and DisplayPort inputs.

the specs page I found put strict limits on the length of the DVI cables that could be used. Since HDMI <--> is a 'just wires' conversion that limit the TOTAL length of the HDMI <-> DVI cable to 1.8 meters.

it says power required is 39 watts. Where is it getting its power? is that source adequate and stable?

does your dock do DisplayPort output?

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Answer 6

giants450 Author

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8 points

Jun 30, 2024 6:20 AM in response to Grant Bennet-Alder

Thanks for the response! The thing is, the display IS detected. It shows up when I click "Display" in Settings, and I can change the resolution etc. I can even drag windows onto the display, but the monitor is blank and goes to sleep. So from the Mac's perspective, everything seems normal. But visually, nothing is shown. I nonetheless tried your suggestions, but they did not work :-(

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Answer 7

giants450 Author

Level 1

8 points

Jun 30, 2024 8:17 AM in response to Grant Bennet-Alder

I tried a short (~ 1 ft) USB-C cable, no diffreence.

I don't have another HDMI-->DVI cable to true, but the current one (a) still works when I plug my PC into the hub, (b) worked for 3 issues w/o fail and only stopped working when I got a new work PC. The monitor is older so it is not an HDMI-only display, it in fact lacks an HDMI input, which is why I need to have an HDMI->DVI cable go from the hub to the monitor.

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Answer 8

giants450 Author

Level 1

8 points

Jun 30, 2024 9:18 AM in response to Grant Bennet-Alder

Its an HP LA2405. I've tried every resolution (including as low as 800x600). The cable is working with the other USB-C hub and the PC, so I don't think its the cable.

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Macbook Pro stopped displaying to external monitor after using USB-C hub with a new PC

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