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2 identical external monitors displaying different resolutions - M3 Max

Hi,

I plugged in 2 identical innocn 27C1U-L external monitors to my 2024 M3 Max via a Kensington dual 4K dock. Both monitors work, but one is crystal clear and the other is blurry. In system settings, the resolutions are both set as the same values (1920x1080 (default)). See attached screenshots. However, one of the two monitors has more options than the other (the "optimize for" button never appears for one of them, regardless whether it's the main display or the extended display). In the About in the System Settings, one display comes up as 3840x2160 and the other as 1920x1080. See the third screenshot. Again, this is a little weird, because both of the monitors have a default setting of 1920x1080 in the System Settings.


Also, the first time I plugged in, the monitor on the left was displaying clearly, and the one on the right was blurry. After restarting, it's been the opposite since. But at least this shows that both of the monitors can handle the higher res output.


I understand that M3 Max can handle 2+ external monitors at high resolutions, but I can't for the life of me figure out how to get both to display in higher res. I've rebooted, switched cables around, switched ports, unplugged and used "option" key in display settings to "Detect Displays."


Does anyone have any idea of how to make this work? It's incredibly frustrating. Thanks!




MacBook Pro (M3 Max, 2023)

Posted on May 7, 2024 1:41 PM

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May 7, 2024 3:56 PM in response to jnatio

jnatio wrote:

Yes, that's exactly right @ Servant of Cats. 3 downstream ports and 1 upstream. I might have misspoken?


You didn't mis-speak. I just like to go straight to an online manual and/or technical specifications (if I can), and confirm what the arrangement is, to make it easier for myself and others to troubleshoot.


Sometimes you'll find little "gotchas" in the online documentation, though I didn't see any in this case.

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May 7, 2024 1:58 PM in response to Grant Bennet-Alder

Kensington SD5700T Thunderbolt Four Dual 4K Dock

Cable Matters Thunderbolt 4 6(?) foot cables connected between monitors and dock, 3 foot thunderbolt 4 0.8M passive cable connecting dock and laptop (I think it came with the dock, no brand visible).


Also here is the display information from the system report:

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May 7, 2024 2:15 PM in response to jnatio

A genuine Thunderbolt dock like that CAN support two 4K displays, provided all other requirements are met.


0.8 meters Thunderbolt lead-in cable to the dock is the right one to be using.


You need comparably short cables (0.8 Meters) from Dock to each display, otherwise those links may see signal degradation that could cause the resolution to be reduced, or the display to drop out.

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May 7, 2024 2:22 PM in response to Grant Bennet-Alder

Thanks.


I just switched out the cable connecting one of the monitors to the dock with a shorter one. Unfortunately I don't have 2 shorter cables. But the situation persists.


Apart from cables, which worked fine with a previous laptop at the same dock with the same monitors, is there anything else that could cause this? Particularly on the Mac end.

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May 7, 2024 2:41 PM in response to jnatio

jnatio wrote:

Kensington SD5700T Thunderbolt Four Dual 4K Dock


This dock has four Thunderbolt 4 ports: an upstream one for the link to the computer, and three downstream ones.


There aren't any dedicated DisplayPort or HDMI ports.


The quick start guide seems to indicate that you should be able to drive two 4K monitors @ 60 Hz. (Assuming that your computer supports multiple external displays, which a M3 Max MBP does.)

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May 7, 2024 3:39 PM in response to Servant of Cats

This dock has four Thunderbolt 4 ports: an upstream one for the link to the computer, and three downstream ones.
There aren't any dedicated DisplayPort or HDMI ports.

The quick start guide seems to indicate that you should be able to drive two 4K monitors @ 60 Hz. (Assuming that your computer supports multiple external displays, which a M3 Max MBP does.



Yes, that's exactly right @ Servant of Cats. 3 downstream ports and 1 upstream. I might have misspoken? I should be able to support 2 4K monitors with this dock and laptop. I just don't know why that's not happening.


I followed some advice found on reddit and removed my

com.apple.windowserver.plist

files from my Profiles directory, in an attempt to "forget" the monitors to reset the resolutions that the computer had assigned to the two monitors. It did "forget" them, but when I re-added them, the same thing happened where one is a higher res than the other.

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May 7, 2024 4:29 PM in response to jnatio

<<. I just don't know why that's not happening. >>


Your cables are too long for errors-free transmission.


LOTS of users have solved recent "can't reach specified resolution" issues by bringing their cables back into compliance for cable length and quality for the very fastest speeds.

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May 7, 2024 5:42 PM in response to Grant Bennet-Alder

LOTS of users have solved recent "can't reach specified resolution" issues by bringing their cables back into compliance for cable length and quality for the very fastest speeds.

OK, will give it a shot and report back. Can you tell me where you are sourcing the "compliance" you mentioned? It'd be good to have a source of clearly stated protocols for these sorts of things. The IT folks at my work (who made the dock/cable purchases) take their hardware choices seriously, so it'd be good to have a something to point them to. And it would help me get reimbursed for cables....

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May 7, 2024 5:47 PM in response to jnatio

<<. It'd be good to have a source of clearly stated protocols for these sorts of things. >>


I could not agree more.


Most if what I learned about this was picked up by closely reading Wikipedia articles for each protocol/cable type, and reading far enough into those article to see what happens when resolutions are expanded to the highest levels, 4K and beyond.

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2 identical external monitors displaying different resolutions - M3 Max

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