Got a new 4K screen, but CustoMac does not allow select 4K resolution

Joined
Feb 2, 2019
macOS
10.14.6
Mobo
ASRock Z370M-ITX/ac
CPU
i5-8400
GPU
UHD630
#1
I just got me an LG 27UL650-W, which is a 27" 4K screen and connected it to my CustoMac.
The display settings indicate the system finds the color profile for 'LG HDR 4K but the Display settings do not show an option for 3840x2160 resolution (selecting manual scaling shows max resolution2560x1440)
In my SMBIOS I hae iMac18,1 selected as my system, which is an 21" imac.
Do I need to update to a 27" 4K version or is there something else I need to update to allow full use of the new resolution?

Thanks!
 
Joined
Apr 10, 2018
macOS
10.15.1
Mobo
GA-Z97X-UD5H
CPU
i7-4790K
GPU
Powercolor RX 580 8GB
#2
This is probably more to do with the cable being used not working to 4K standard (assumed HDMI as not specified) rather than it being an issue with the display, your system settings or with macOS.

I would look at the cable and which port you are connected to on your motherboard, assumed using IGPU.

Most if not all HDMI cables will support 2K (2560x1440).

The same cannot be said for support of 4K resolution, these higher standard cables you usually have to pay a bit more for.

Your ASRock motherboard supports the following connections: via the IGPU

- Three graphics output options: DisplayPort 1.2 and 2 x HDMI ports
- Supports Triple Monitor
- Supports HDMI with max. resolution up to 4K x 2K (4096x2160) @ 30Hz
- Supports DisplayPort 1.2 with max. resolution up to 4K x 2K (4096x2304) @ 60Hz

Personally I would connect the LD display using a good quality DisplayPort cable, as it offers the higher refresh rate compared to HDMI. The ASRock motherboard and LG display both support DisplayPort. It is also less likely to give you issues within macOS, as it is a native connection used by Apple.
 
Joined
Feb 2, 2019
macOS
10.14.6
Mobo
ASRock Z370M-ITX/ac
CPU
i5-8400
GPU
UHD630
#3
Thanks. I’m actually using a DisplayPort cable, but am not presented with the 4K option. Will try with the supplies
mot just struck me that the iMac 18.1 I use in my smbios does not support 4K and if I should change it and what I should be aware of if I do.
 
Joined
Apr 10, 2018
macOS
10.15.1
Mobo
GA-Z97X-UD5H
CPU
i7-4790K
GPU
Powercolor RX 580 8GB
#4
I would again suggest you have a look at the quality of the DP cable. Not all cables DP are capable of supporting 4K resolution.

I would also suggest runing through the LD display menu option's, to check that the display is set to show the highest resolution possible.

The real iMac 18.1 uses a dGPU not just the IGPU. It will have a Radeon Pro 555 or 560 graphics processor with 2 GB or 4 GB of dedicated VRAM, depending on the exact model build. Assuming you are looking to imitate a Kaby Lake i5-7400 with HD 630 IGPU you are not going to match the graphics power of the iMac. The real iMac will run the built-in 4K display and an external 4K display at the same time.

I think your Cofffee Lake CPU is a better match for an iMac 19.2, which has the I3-8100, I5-8500 and I7-8700 CPU as build options. There is very little difference between your i5-8400 and Apple's i5-8500. As you are running Mojave 10.14.6 there is no bar to using the iMac 19.2 SMBIOS. However, this model also uses a discrete GPU, a Radeon Pro 560X graphics processor with 4 GB of dedicated GDDR5 video memory.

So your IGPU only system will fall short of the same performace as the real iMac 18.1 or 19.2. It should however be able to run a single 4K display @ 60Hz using the DisplayPort connection.
 
Joined
Feb 2, 2019
macOS
10.14.6
Mobo
ASRock Z370M-ITX/ac
CPU
i5-8400
GPU
UHD630
#5
I tried with the LG supplied DisplayPort cable and god
the screen menu does not have a setting for resolution, but does popo

I also tried the supplied hdmi cable (never had the hackintosh connected through hdmi before) and it displayed a fully purple tinted picture
 
Joined
Apr 10, 2018
macOS
10.15.1
Mobo
GA-Z97X-UD5H
CPU
i7-4790K
GPU
Powercolor RX 580 8GB
#6
Your IGPU settings are wrong then if you are getting a purple screen.

That is a sure sign that the ig-platform-id in the graphics section of the config.plist or the AAPL,ig-platform-id in the Devices > Properties section is wrong for your system and SMBIOS.
 
Joined
Feb 2, 2019
macOS
10.14.6
Mobo
ASRock Z370M-ITX/ac
CPU
i5-8400
GPU
UHD630
#7
The AAPL,ig-platform-id is set to 07009B3E, which I believe is the correct value for Intel UHD630 on Coffee Lake.
I had previously selected a new value from the dropdown in Graphics>ig-platform-id (based on Coffee Lake Desktop 3E920003) but got a kernel panic. I got the system booted by editing the value in the Bootloader. I've tried different values there from the Coffee Lake list, but without luck. (also when kept blank).
It looks like full VRAM gets assigned, but max resolution is still 2560x1440

1581971616109.png
 
Joined
Apr 10, 2018
macOS
10.15.1
Mobo
GA-Z97X-UD5H
CPU
i7-4790K
GPU
Powercolor RX 580 8GB
#8
That tab is just reporting what is being used by the system. It doesn't dictate what resolution the system uses.

Have you checked your System Preferences > Display options and looked at the Scaled feature list?

Screenshot 2020-02-18 at 14.39.27.png My System Preferences Display tab, Scaled option selected.

This tab shows all the resolutions available on my system. I use 2560x1440, the maximum my dual dispaly setup can use. This is also the 'Default' resolution for my two Dell U2515H displays.

If the 4K resolution is not showing in the list when you select 'Scaled' then issue is either with the the IGPU or cable/connection selected/used. Not the settings in macOS. The Display preference pane will only allow you to select a supported resolution, this resolution has to be supported by the IGPU, cable used and display connection type.

Have you been able to run the display at 4K in Windows or Linux? Might be worth checking to see if the same issue arises when running another OS.
 

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