Is it possible to reset the HDMI refresh rate via Terminal?

Question

Level 7

22,531 points

Is it possible to reset the HDMI refresh rate via Terminal?

While setting up a 2018 Mac mini (Sonoma), in Display Settings I inadvertently set the HDMI refresh rate to 30Hz. My display does not support 30Hz and the screen went black. The Mac did not automatically revert to 60Hz, and hitting the ESC key did nothing. (This is a Sony Bravia 1080p TV.)

All I could do was power off the Mac mini via the power button.

Now, when I boot the Mac mini, the startup Apple logo & progress bars appear, but then the screen goes black again and the TV displays this message - "Unsupported signal. Check the device output." Of course, with a black screen I can't do that.

I tried each of the following but none have corrected the problem. Every time, the screen just comes up black as above.

Boot into Safe Mode
Reset NVRAM
Reset SMC

I *can* boot into Recovery Mode, and from there I *could* use Terminal ...

Does anyone know a command to reset whatever (hidden) setting controls the HDMI refresh rate so I can reset it to 60Hz?

iPhone 16

Posted on Mar 7, 2025 4:14 PM

Reply

Answer 1

den.thed

Level 10

84,814 points

Mar 7, 2025 4:48 PM in response to MartinR

Hmm... I'm surprised that the NVRAM reset didn't reset the Display settings to default.

Maybe try that again and hold the keys until it chimes two or three times.

see > Reset NVRAM on your Mac - Apple Support

If that doesn't help,

1) try a different HDMI cable

2) connect a different Display or TV to the Mac mini

3) connect a second Display or that TV to the Mac mini using a USB-C to HDMI adapter.

For some other ideas,

see > If your external display is dark or low resolution - Apple Support

and > If there’s no picture on your Mac after you change the resolution - Apple Support

Edit: for an after thought

shut off the Mac mini, turn off the TV and unplug the cable from the Mac mini,

reconnect the cable, turn on the TV and set to that cable input, then turn on the Mac mini.

Reply

Answer 2

MartinR Author

Level 7

22,531 points

Mar 7, 2025 6:44 PM in response to den.thed

Thanks for the suggestions. Nothing has worked so far - different HDMI cable, multiple NVRAM & SMC resets, multiple attempts to boot into Safe Mode, shut down & unplug everything, etc. Unfortunately I don't have another display to connect to.

I tried connecting the mini to the TV using a USB-C-to-DVI adapter + a DVI-HDMI cable and that actually works ... and it runs at 60Hz refresh (verified in System Information). But there is no option to change the refresh rate, and in any event the Mac only shows options for the currently connected display. It appears the Mac "sees" the TV as a different display when connected via the Adapter vs. directly via HDMI even though it's the same TV.

System Settings has to be storing the refresh rate somewhere. But it's not in NVRAM, I inspected NVRAM and there are no display settings there.

Reply

Answer 3

den.thed

Level 10

84,814 points

Mar 7, 2025 8:39 PM in response to MartinR

Strange that one of those, did not default the refresh rate.

Do you have another Mac that is setup to access the Mac mini with screen sharing..?

If so, see if you can get into the Mac mini that way and change the refresh rate.

Reply

Answer 4