HDMI Connection locked to 30hz, DisplayPort not working Monterey 12.5.1

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4 points

HDMI Connection locked to 30hz, DisplayPort not working Monterey 12.5.1

Last week (Friday) I updated my MacBook Pro 15" (2017) to Monterey 12.5.1. It had been running the previous release of Monterey up until that point.

Now (Monday morning), my external displays no longer connect properly. The monitor is a Dell U2718q (27", 4k resolution).

The monitor no longer detects any display signal via the DisplayPort -> USB C cable that worked prior to the update. Older messages on various boards suggest setting the monitor to DisplayPort 1.2, but in fact that is the highest DisplayPort version supported by this Dell model.

I experimented with various configurations, and finally tried an HDMI cable through an Apple USB-C Digital AV Multiport Adapter. The monitor got a signal and functions, except that the refresh rate won't go above 30Hz.

I have a separate Macbook Pro M1 Max with a built in HDMI port, so I tested the cable and monitor on that laptop, and I was able to get 60Hz refresh rate.

Has there been a software regression with display driver code? This severely impacts my day to day work. Do I have any options here?

Posted on Aug 29, 2022 8:31 AM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

140,891 points

Aug 29, 2022 8:59 AM in response to iwclibro

MacBook Pro 2017 and later should provide very good support for 4K displays.

The display maker's web site says:

Connectivity

1 x DP (ver. 1.4)

1 x mDP (ver. 1.4)

2 x HDMI (ver. 2.0a)

DisplayPort 1.4 (over DisplayPort 1.2) adds DisplayStreamCompression (DSC) which raises the effective top speed. BUT the display has to provide de-compression-on-the-fly. Some older displays might not support this, but your display claims to support it.

so not supporting 4K @ 60 on a particular USB-C to DisplayPort cable calls that cable/adapter into question.

The Apple USB-C Digital AV Multi-port Adapter was released as an early version and a later version. Only the later version HDMI supports 4K @ 60:

https://support.apple.com/en-us/HT207806

.

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Answer 2

iwclibro Author

Level 1

4 points

Sep 1, 2022 11:27 AM in response to Grant Bennet-Alder

I was finally able to add in some more testing scenarios, and I finally isolated the problem. I thought I would note it here for others.

I fetched a PC with a USB-C DisplayPort connector. I found that the signal didn't show up for the PC, but it would drive a second monitor I had laying around with the same cable.

I then unplugged, and not just turned off the original monitor, and reconnected everything. Now the 2017 MacBook Pro is driving a signal again via the DisplayPort. The issue was specifically with the Dell Monitor. The key was fully unplugging it and not just powering it off.

This issue can be considered resolved now. I really appreciate the help diagnosing it.

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Answer 3

Aug 30, 2022 10:54 AM in response to iwclibro

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

• on invoking Option-(Detect Display) button 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 4

iwclibro Author

Level 1

4 points

Aug 29, 2022 11:21 AM in response to Grant Bennet-Alder

I got a new Digital AV Multi-port Adapter, and I can confirm that it enables 60Hz on HDMI now. I am still waiting on a new DisplayPort cable to see if that makes a difference there.

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Answer 5

iwclibro Author

Level 1

4 points

Aug 30, 2022 10:42 AM in response to Grant Bennet-Alder

Today I received a brand new DisplayPort cable. I plugged it into both of my MacBooks, and neither could push a display signal to my monitor. I highly doubt that two cables have failed in short order. I think there is a software/os issue with DisplayPort negotiation. Note that the HDMI path works, but I very much would prefer to use DisplayPort.

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Answer 6

iwclibro Author

Level 1

4 points

Aug 30, 2022 11:20 AM in response to Grant Bennet-Alder

I tried two different DisplayPort cables. I tried two different MacBooks. I powered the monitor off and then powered it on and connected the cable.

M1 MacBook Pro -- "No signal from device" displayed by the monitor, the Option-(Detect Displays) button did not change in Displays preferences

Macbook Pro 2017 (via Digital AV Multi Port Adapter) -- "No signal from device" and Detect Displays would not appear

Macbook Pro 2017 (direct connection, and tried multiple ports) -- "No signal from device" and Detect Displays would not appear

Connect to Macbook Pro 2017 via Digital AV Multiport Adapter + HDMI -- signal appears

Connect to M1 Macbook Pro via Digital AV Multiport Adapter + HDMI -- signal appears

Connect to M1 Macbook Pro via build in HDMI port -- signal appears

It is important to note that the original DisplayPort cable connection direct to the 2017 Macbook worked fine Friday morning. I installed the latest 12.5.1 update on Friday evening at the end of the day. Come Monday morning, my display would no longer connect.

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Answer 7

Aug 30, 2022 11:21 AM in response to iwclibro

The other place to look that is a little more complex is:

 menu > about this Mac > (system report)...

... Graphics and Displays

.

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Answer 8

iwclibro Author

Level 1

4 points

Aug 31, 2022 11:07 AM in response to Grant Bennet-Alder

I don't see any additional displays show up when it is connected. Example below from the M1 MacBook Pro.

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Answer 9

Aug 31, 2022 11:53 AM in response to iwclibro

When displays are not even seen in Graphics/Displays, it indicates no path to that device, can't even get the slow speed EDID data from the device -- it is essentially 'not there'.

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HDMI Connection locked to 30hz, DisplayPort not working Monterey 12.5.1

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