MacBook Pro 14" 2021 - unable to get 75Hz on Asus MX38VC

You may have found that the cable "shipped in the box" is a "lowest bidder" cable rather than a highest quality cable.

You are getting close to the limits of what is possible over a regular USB cable. I suggest you use a high-quality USB-C cable intended for Video and not longer than 1 meter in length.

(and don't mistake the Apple Charge-only cable for a data cable -- it most certainly is NOT.)

Monoprice Essentials USB Type-C to Type-C 3.1 Gen 2 Cable - 10Gbps, 5A, 30AWG, Black, 1m (3.3 ft) - Product # 24285 - $18.49

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.

If the display is not properly self-reporting that it can support higher refresh rates over USB-C, you may be able to use third-party tools to bypass what the display reports and set different resolutions and refresh rates. SwitchResX is a popular choice, but it can be complex.

Also this is one rare case where what is supported over HDMI may be higher (up to 4K at 60Hz) than what the display claims to support over USB-C (due to its improperly reporting its capabilities).

Same exact problem w/ MacBook Pro 16" 2021 (M1 Pro) and MacBook Air 2020 using multiple cables including brand new thunderbolt 4.

For those of you that keep getting stuck on a cycling screen or unable to get clamshell mode working at all, I've gotten around it using screenresolution utility (also available via homebrew). Cue up this in your terminal so you can hit enter to recover your monitor:

screenresolution set 3840x1600x32@30

Obviously this is still just 30Hz, and you will need to then open display settings and mess with resolution (change it away and back from the desired setting) to get the 30 Hz to persist for each configuration you use your MX38VC.

This isn't anything exciting to report, but I recently fired up my previous machine (Mac mini 2018 - intel i7 3.2Ghz) and I hooked it up to the Asus MX38VC using the exact same cable/dock that I currently use with my new MacBook Pro 14" (M1 Max). I upgraded macOS on the Mac mini to v12.3.1 and I can confirm that the Asus worked fine with a refresh rate of 75Hz....but as soon as I revert to the MacBook Pro, it drops back to 30Hz. So it seems this problem specifically affects Apple Silicon based machines - works fine on an intel machine, even running macOS v12.3.1. I'm still hopeful we'll get a fix at some point...

The reported numbers in SwitchResX are what the display is self-reporting as its capabilities over the current interface.

I don't see the 3840 by 1600 at 75Hz with HiDPI you are looking for. That means the display is not claiming to support that, despite what its paper documentation states. A firmware update to the display (like what Benq did) might change those numbers.

You might be able to ADD that to the list with SwitchResX, and get MacOS to use it. The process was always a bit convoluted.

Yes, Monterey 12.0.1

It definitely is not a cable issue... I tried all manner of cables, thunderbolt, USB-C, display port, HDMI.... And made sure they were the latest and supported the highest bandwidths. And yea, same issues, if I try to switch to 75Hz it cycles between trying to connect to the ASUS, then back. I'm surprised that Apple doesn't have a dialog box for confirming the display changes. I have to go into Recovery mode to switch it back to 30 Hz.

Are you sure it didn't work before the upgrade? not to be an ***, but maybe you didn't notice it before. I use it at 30Hz and I'm kind of use to it. If it did work before Monterey, that's interesting, it gives hope that maybe a future upgrade would fix it. I do like the monitor... If only...

I just got off the phone with Apple Support. It seems my report will get to the developers with it being flagged as a Monterey issue. krisss85 it seems like our Macs are now behaving identically after my Monterey install. I can confirm full 75hz functionality (clamshell included) with direct USB-C connection on the Asus MX38VC with the 2020 MacBook Air M1 under Big Sur. Sucks that yours came with Monterey and had been effectively gimped out of the box.

Hi all,

Are all of you guys running Monterey? This issue with the Asus MX38VC and my M1 MacBook Air only just popped up after I ‘upgraded’ to Monterey a few days back. On Big Sur everything was working perfectly. Now with Monterey the Asus only works at 30hz. 75hz sets off some weird loop that switches between the displays on just the MacBook Air’s screen. Given that the only change in my setup was upgrading to Monterey, I think it safe to say that it is not a cable issue or an issue with the MacBook Air or the monitor individually. I believe the issue is that Apple broke something in Monterey and haven’t gotten round to fixing it.

Also the functionality is not all there at 30hz. Clamshell mode doesn’t work anymore as closing the lid cuts the monitor signal now. It’s pretty annoying that this happened with and operating system upgrade.

Any thoughts would be much appreciated.

Update from Apple engineering: they are aware of the issue, acknowledge that it's affecting multiple people, (supposedly) working on an update, but no official ETA. 😒

Hello krisss85,

It sounds like when you use a 75Hz resolution on your MacBook Pro you lose signal to your external monitor.

Here are a couple resources to review that might help.

• Review MacBook Pro 14- and 16-inch - Technical Specifications to ensure your set up and cables falls within the display and video support for this Mac as well as Change the refresh rate on your MacBook Pro or Apple Pro Display XDR
• Also review If your external display isn't detected or appears blurry on your Mac

If it still doesn't work, you may want to Contact Apple Support or use this Get Support link for assistance.

Hope this information helps.

Have a good day.

Spent the day on the phone with Apple and Asus support. I'm not sure if this is the exact problem others are facing, but Asus support claims that the usb connection only supports 30 or 60Hz while MacOS is offering 30 or 75Hz. This information got escalated to engineering at Apple and hopefully I will hear back within the week and update anyone else still suffering.

I think most of us know this lol. We are just venting and raising general awareness of the issue here. Most of us have case reference numbers with Apple support and some of us even have tried contacting Asus for help. I’m strongly of the opinion it is Apple’s fault more so than any fault on Asus’s end due to the history of everything being fine and dandy under Big Sur. The guys that got their Macs with Monterey pre installed couldn’t have known any different and therefore would have considered it being an Asus issue.

Anyway just to summarize

Big Sur = everything ok

Monterey = 30hz mode only and no clamshell mode

You can get clamshell mode working @ 30Hz.

brew install screenresolution

then type but do not hit enter yet

screenresolution set 3840x1600x32@30

Close the laptop, wait a second and hit enter.

To get this fix to stick the next time you try to use clamshell, you need to also now open display preferences, change something other than refresh rate and change it back (causing the settings to save including the refresh rate).