Mac Studio M2 Ultra won't display 8th monitor

Question

Level 1

4 points

Mac Studio M2 Ultra won't display 8th monitor

I have a Mac Studio M2 Ultra, which is supposed to support 8 displays. I can get 7 working, but not the 8th one.

My setup:

Front Thunderbolt Port 1: LG Ultrafine connected via TB with a simple FHD Sansui display daisy chained.

Front Thunberbold Port 2: N/A (this is where I'm trying to connect the 8th display, but the display says it is getting no signal.

Rear Thunderbolt Port 1: LG Ultrafine with Sansui FHD display daisy chained.

Rear Thunderbold Port2: LG Ultrafine with Sansui FHD display daisy chained.

HDMI: the 7th display, a Sansui FHD display, is connected to HDMI.

The info from Apple is that the Mac Studio M2 Ultra supports up to 8 displays with the following configuration:

a) Four displays connected to TB ports in the rear (which I have with the two sets of daisy chained displays),

b) Two displays connected via front TB port with daisy chain (which I have),

c) One display connected to HDMI (which I have),

d) One display connected to the other front TB port (which I have, but this one is not getting a signal apparently).

It's not the display; if I connect the USB-C cable coming out of one of the LG Ultrafine displays, this display works fine.

I've tried using a TB cable (same exact cable used for the other three LG Ultrafine displays) to no avail. I also tried a USB-C cable, also to no avail.

I do notice that if the mac is on and 7 displays are up, they do seem to flicker once briefly like they are resyncing if I then plug in the 8th display to the second front TB port.

I've plugged/unplugged/replugged the display multiple times from both ends of the cable. I've shut down and rebooted the mac at least twice. I've tried "detect displays" in the settings app. Nothing is working.

The Apple documentation pretty clearly says that this should work. Any ideas, or is the official documentation just wrong?

Posted on Dec 12, 2025 5:56 PM

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Answer 1

Dec 13, 2025 4:16 PM in response to domehead100

Cables for a Thunderbolt Display should be EXACTLY the included 0.8 meter Apple-Engineered ThunderBolt cable, or a brand-X Thunderbolt cable no longer than 0.5 meter, maximum.

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For a display on a USB-C cable to be detected and run reliably, the USB-C cables need to be ONE meter or shorter.

Substituting a Thunderbolt cable does not improve things enough to make that cable any longer.

With the exception of the Apple-Engineered 0.8 meter Thunderbolt cable shipped with Apple displays, regular 'shipped in the box" cable are often "lowest bidder" cables that were substituted for the ones the Engineers tested with. You should assume they are not good enough for use for display data.

The appropriate cable for a USB-C Display is certified, and marked with SuperSpeed+ or USB-10 or USB-20 logo, and ONE meter or shorter.

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Answer 2

Dec 12, 2025 6:39 PM in response to domehead100

Move one UltraFine off the front ports

Rebalance like this:

Rear TB ports: keep UltraFine + Sansui chains
Front TB port 1: single Sansui only
Front TB port 2: UltraFine
HDMI: Sansui

This reduces stream pressure on the front controller.

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Answer 3

Dec 13, 2025 7:48 AM in response to domehead100

What exact model LG Ultrafine? is this the Apple LG Ultrarfine 4K display?

are you using EXACTLY the included Apple-Engineered ThunderBolt cable, or a brand-X Thunderbolt cable no longer than 0.5 meter, maximum?

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Answer 4

domehead100 Author

Level 1

4 points

Dec 13, 2025 5:35 AM in response to azaksalmarzur28

Thanks for your reply, but your configuration only adds up to 7 displays, which is what I already have working.

Even with the one Ultrafine+Sansui daisy chain unplugged from one of the front TB ports, the single Sansui plugged into the second still says it receives no signal. Also, this one daisy chained setup is what the Apple documentation specifies in order to get 8 displays.

I'm thinking that the Sansui, which has a "USB-C" input, works fine when chained with an Ultrafine, but does not work when connected directly to the Mac's TB port, so maybe I need to get an additional Ultrafine instead or some other display that works with "Thunderbolt" vs "USB-C."

Several reviewers on Amazon, however, state that they successfully connected the display to their MacBook TB ports (they call them USB-C ports), so I assumed that direct connection to the TB port on the Mac Studio would work, but it is not working.

On Linux, I would have several avenues for looking at system logs to try and figure this out, but on Mac I'm just not well versed in where to look.

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Answer 5

domehead100 Author

Level 1

4 points

Dec 13, 2025 3:06 PM in response to Grant Bennet-Alder

The three Ultrafines are model 24MD4KL-B, which I believe were developed in partnership with Apple, but not sure. They are all working perfectly and have been for the last 2-3 years that I've had them.

For the Sansui as the 8th display, I've tried several cables, including the original one included with the Ultrafine, which I believe is a 2-meter cable. I have it available since I used shorter high-quality cables for the Ultrafines since they are close to the Mac Studio.

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