iM 4,1-14,4 How to get 1440p out on external monitor for 2011 iMac?

[T'hain Esh Kelch]

So I got a Philips 245E1S/00 display hooked up to my 27" 2011 iMac, through a HDMI cabel --> HDMI to Thunderbolt 2 adapter.
The display supports up to 2560x1440p at 75 hz over its HDMI1.4 port. But I am only getting 1920x1080p out of it at 60 hz, when connected to the iMac. I don't mind the 60 hz frequency, but I would like the full resolution.

As I understand it, this should work, but it doesn't. At what step am I limited here?

 

[generallystupid]

So I got a Philips 245E1S/00 display hooked up to my 27" 2011 iMac, through a HDMI cabel --> HDMI to Thunderbolt 2 adapter.
The display supports up to 2560x1440p at 75 hz over its HDMI1.4 port. But I am only getting 1920x1080p out of it at 60 hz, when connected to the iMac. I don't mind the 60 hz frequency, but I would like the full resolution.

As I understand it, this should work, but it doesn't. At what step am I limited here?

Try using an app like SwitchResX to create a custom resolution sometimes that can force the display to output 1440p.

 

[Amethyst1]

So I got a Philips 245E1S/00 display hooked up to my 27" 2011 iMac, through a HDMI cabel --> HDMI to Thunderbolt 2 adapter.

That’s a passive adapter, limiting you to 165 MHz pixel clock. That limitation is in the iMac’s GPU.
You need an active DisplayPort to HDMI converter because 2560×1440 at 60 Hz requires 241.5 MHz pixel clock (CVT-RB).

However: The monitor also has DisplayPort. Why don’t you use that?

 

[T'hain Esh Kelch]

That’s a passive adapter, limiting you to 165 MHz pixel clock. That limitation is in the iMac’s GPU.
You need an active DisplayPort to HDMI converter because 2560×1440 at 60 Hz requires 241.5 MHz pixel clock (CVT-RB).

Thanks!

However: The monitor also has DisplayPort. Why don’t you use that?

I assume that is the TB2 port? I honestly thought I could just use an adapter for the TB2 port, and it would automatically be using Displayport.

 

[Amethyst1]

I assume that is the TB2 port? I honestly thought I could just use an adapter for the TB2 port, and it would automatically be using Displayport.

The iMac has Thunderbolt 1. You can connect a DisplayPort monitor directly because the Thunderbolt controller operates in passthrough mode in this case. Additionally, it can output single-link DVI/HDMI signals if using a passive adapter like yours (this is called dual-mode DisplayPort) but that is subject to a 165 MHz pixel clock limit due to the GPU.

 

[T'hain Esh Kelch]

Thanks a lot! I will see if I can get a proper adapter.

 

[Amethyst1]

Thanks a lot! I will see if I can get a proper adapter.

Or a DisplayPort cable

 

[T'hain Esh Kelch]

Or a DisplayPort cable

Funny you should mention it, because I can see from my receipt from when I bought the display 4 years ago, that I also bought a displayport to mini displayport cable.. I wonder why I ended up not using it. Hmmmm. Just found it in my drawer, and will test it out.

Edit: Yup, now its running at full resolution, thanks a lot! I really wonder why I went with the other solution though. I must have bought that HDMI to displayport adapter for some reason.