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CAC-1085 does not output 4k 120 with RTX 3090 and LG C9 or CX

Updated on 06-03-2021 in DisplayPort 1.4 to 4K120Hz HDMI Adapter
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6 on 23-02-2021

Connected a new CAC-1085 to the display port in my RTX 3090, connected an 8k rated cable that I know works with hdmi 2.1 and outputs 4k @ 120 on it’s own.  120hz is not a selectable option in the nvidia control panel.  

Thinking maybe its a graphics card bandwidth issue, so I make sure the CAC-1085 and LG C9 is the only monitor connected, still the same thing.  Running latest nvidia drivers from 1/26/21

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Baak 0 on 25-02-2021

Hey Jaywr3550,

Problem is with the nVidia drivers. To be able to get 4k120Hz trough the adapter you need to go back to the driver 456.38.

Don’t run a longer cable then 2 meters tho.

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laxu 0 on 25-02-2021

The latest driver that works for me is 456.71. Anything above that causes the same issue, 4K 120 Hz is only possible at 4:2:0. With inexplicably 10-bit color and HDR so it seems to be half-broken somehow.

Would love to see Club3D response for this.

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Baak 0 on 26-02-2021

Hi Laxu,

Have you try driver 456.38?

And what is your setup?

What cables do you use?

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Rob 0 on 26-02-2021

Hi guys, I am using driver 456.98
Is working on lg cx RGB full 10 bits

Please post if anyone have tried another working driver here.

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Diablix 0 on 28-02-2021

Hello everyone,

I have working driver 456.71 with 2080 Ti SLI, LG 48CX, 4K@120Hz RGB Full 10bpc. I have found about this driver on [H]ard|Forum.

Good to know even 456.98 works well.

The issue is registered as open issue since 461.40: Displayport-to-HDMI 2.1 protocol converter clock limited to 600MHz pixel clock [3202060].

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JoachimOtahal 0 on 06-03-2021

Thank you so much for that information.

Got the Samsung Q95T 75″ today, and bought the CAC-1085 with the CAC-1373 a few days before, running on Titan RTX. I couldn’t wrap my head around what is going on, checking with CRU from https://www.monitortests.com/forum/Thread-Custom-Resolution-Utility-CRU seeing only HDMI limited capabilities, tried to hack the monitor information added custom resoltions to get RGB, thought “oh shit, maybe cable too long”… And then got lucky to find this thread.

Confirming: Driver 456.71 works “right out the the box”. I will try the Hotfix-Driver 456.98 when something weird happens.

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