Macbook M4 Pro external display wake-up and signal issues

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miyagor Author

Level 1

12 points

Macbook M4 Pro external display wake-up and signal issues

I'm having same issue on M4 Pro 48 GB with the external displays connecting and "wake up" problems. My setup is:

2x 4k 27" OLED one 120 hz another 144hz set.

Connected over USB-C with KVM - ASUS PG27UCDM

And another HDMI High Speed Certified (which handles even 240hz if 1 display) - DELL Alienware AW2725Q

When I connect both at the same time they display good, but sometimes when macbook goes sleep when I'm out of desk and comeback the Dell is getting "No signal" even that Macbook detects it in the Displays, turning on & off doesn't help. When trying to reconnect the cables sometimes the Dell goes ON and the ASUS has "USB-C no signal" but the USB-C charging + KVM is working, macOS sees it but no signal.

I need to reconnect the cables both at the same time (which is not always working, sometimes have try few times) to get them both working and display until again macbook goes to the sleep/standby mode. Its getting me very annoying because Apple says it support 2x 4k 144hz on my Macbook M4 Pro. I have updated all monitor's firmware and the MacOS to the latest version but its still the issue!

Where can I fill the report somewhere to the Apple so they take care of this bug? Its really annoying that I'm not getting what I have especially paid extra for.

MacBook Pro 16″, macOS 26.5

Posted on Jun 23, 2026 3:23 AM

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Answer 1

Jun 23, 2026 6:58 PM in response to miyagor

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)

when using a KVM switch, the display can only be detected if the cable (including EDID secondary data channel) is complete all the way to the display, so that the display can respond when the Mac sends that query.

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Answer 2

Jun 23, 2026 7:08 PM in response to miyagor

that ASUS PG27UCDM appears to be a 3840 by 2160 (4K) display at 10 bits/color, and refresh rates to 240 Hz.

interfaces include:

2x HDMI 2.1

DisplayPort 2.1

USB-C with power delivery and DisplayPort Alt mode, but severely limited by maximum USB speeds.

When adapting display data from USB-C, each display interface uses a different set of standard speeds, as part of their standards. Each allowed speed must fit inside the maximum speed of USB-C, which is 20 G bits sec.

for DisplayPort, the highest standard speed that can be supported by the protocol (when starting with USB-C) is 17.28 G Bits/sec HBR2. That allows a 10 bits/color 4K HDR display to run directly at up to 60 Hz. If your display supports a Display Stream Compression as well, it should be able to run as fast as 180 Hz, but the number of colors may begin to suffer as more compression is applied.

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Answer 3

Jun 23, 2026 6:55 PM in response to miyagor

DELL Alienware AW2725Q appears to be a 3840 by 2160 4K display at 10 bits/color, with refresh rates to 240 Hz.

interfaces include:

2x HDMI 2.1

DisplayPort 1.4

its USB-C does not appear to be a display protocol

Best connection method is to connect to the Mac's DIRECT HDMI port with a Certified ULTRA or 48G HDMI cable.

This will support up to 144 Hz directly, and up to 240 Hz with Display Stream Compression.

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