Can't achieve full resolution (2560x1440) on external monitor from iMac

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Can't achieve full resolution (2560x1440) on external monitor from iMac

Hello everyone,

I have a Late 2009 10,1 iMac (Core 2 Duo, Radeon HD 4760 256 MB, SSD installed, 8 GB Ram).

The issue at hand is that it does not push full resolution on my external monitor (Acer H277HU which is 2560 x 1440). It only pushes up to 1080p.

Initially I had thought that my cable was the problem however I just bought this one (https://www.belkin.com/us/cables/audio-video-cables/mini-displayport-to-hdmi-cable-4k/p/p-f2cd080/) which should solve the issue as it supports greater resolutions but unfortunately it has not.

Any ideas would be appreciated,

Thank you

Posted on Jul 15, 2021 4:47 AM

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Answer 1

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den.thed

Level 10

82,468 points

Jul 15, 2021 6:15 AM in response to leo015

You're welcome.

Because the 2009 iMac's GPU and software does not support 2.5k HDMI.

It only understands older Mini DisplayPort Resolutions up to 2560 x 1600.

If holding the Alt (option) key and clicking on the Scaled button does not reveal resolutions above 1080p with that connection. Then you should be able to get up to 2560 x 1440 or 2560 x 1600 using a Mini DisplayPort to Display Port cable connected the that monitors Display Port input.

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Answer 2

den.thed

Level 10

82,468 points

Jul 15, 2021 5:15 AM in response to leo015

That older iMac may be limited to 1080p, while using that cable and an HDMI connected monitor.

Go to the Display Preference, hold the Alt (option) key and click on the Scaled button.

If you see a higher resolution option try choosing it.

If not, then you need to use a Mini DisplayPort to Display Port cable to that monitors Display Port input.

for example > https://www.amazon.com/Mini-DisplayPort-1-2-Adapter-Cable/dp/B002XVYZ82

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Answer 3

leo015 Author

Level 1

10 points

Jul 15, 2021 5:36 AM in response to den.thed

Hi, thank you for your reply.

Can you please explain why the DisplayPort might achieve this? If the Mini DP on the iMac supports 2.5K, along with the cable connected shouldn't it be working already? Perhalps it's a software issue?

Just brainstorming here

Thanks

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