dead video controller and/or software glitch?

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Level 1

12 points

dead video controller and/or software glitch?

I've got a 2018 Mac Mini running macOS 10.15.7 Catalina. I have it plugged into a 4K TV, along with two other Mac MInis (a 2014 and a brand new M4 version). It was my main computer for years until I got the new M4 Mac Mini. I hooked up the M4 so I can access both the 2014 and 2018 machines via Screen Sharing, and they've both been working fine ever since. Sometimes I connect to it directly via the TV and use a separate kbd and BT Mouse, but It recently stopped connecting to the TV via HDMI. However, it still worked fine via Screen Sharing. The fan died recently and I got a new fan, so I just shut it down and replaced the fan. When I turned it back on and booted it up, it still does not connect via HDMI, but the Screen Sharing is "locked" to 1280 x 1024. It seems to think this is the display that's connected, and I can no longer stretch the desktop to fit my 4k display, which it has always done. I tried another HDMI cable and that didn't help.

I keep this machine because I do Windows software development on a VirtualBox VM that's running Windows 10. Again, I've had no problems for years. I haven't upgraded the OS just because it's stable and keeps on running.

I'm guessing the GPU died a while back, but I don't understand why it suddenly has the Screen Shared video locked at 1280 x 1024. I can't use it at that resolution; I've been using a huge 4k desktop for so long I'm totally spoiled! (at 4k, this is equivalent to 4 x 27" HD (1920 x 1080) displays). All three computers handle it perfectly, except for this one now.

Is there some way to "unlock" whatever has the screen resolution stuck at 1280 x 1024 so I can get back to 4k resolution? Otherwise I imagine it would be a lot cheaper to replace it than get it fixed, and there are a lot of refurbished ones for sale on eBay.

The 2018 Mac Mini has 2T of SSD and 64GB of RAM. (I recently upgrade the RAM from 36GB.)

My M4 Mac Mini reports that the Display is an LG TV Display 72-inch (3840 x 2160), which is correct except that it's only 55-inches.

Mac mini, macOS 10.15

Posted on Jun 6, 2025 2:26 AM

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Answer 1

den.thed

Level 10

86,428 points

Jun 6, 2025 7:47 AM in response to thetoolwiz2

As a test:

I would disable Screen Sharing and connect the 2018 Mac mini to a different TV or HDMI display.

Then if it doesn't display or outputs the wrong resolution, I would reset it's NVRAM.

see > Reset NVRAM on your Mac - Apple Support

Then if that is successful, I would try integrating the 2018 Mac mini back into the previous setup.

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Answer 2

thetoolwiz2 Author

Level 1

12 points

Jun 6, 2025 7:38 PM in response to den.thed

Thanks, I used a different cable to connect to a regular HD monitor and that didn't work.

I tried the NVRAM reset, but it does not seem to have helped. The Screen Sharing border still shows "Locked" at the top and I'm stuck in my choice of 1280x1024 or 1024x768 display now. I'm not sure where the problem lies.

I'm running Catalina, and some searching suggested I can hold down the option key to see more stuff in the Scaled window, and that works sort of -- the highest resolution I can get is 1920 x 1080. There's no 4k -- 3840 x 2160 option

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Answer 3

den.thed

Level 10

86,428 points

Jun 7, 2025 8:32 AM in response to thetoolwiz2

The 2018 Mac mini also supports displays from it USB-C ports.

If the HDMI port is not responding, I would test a USB-C to HDMI adapter or adapter cable.

usb-c to hdmi adapter

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