How to fix LG Monitor flashing green blue problem on Mac mini (Late 2014)

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How to fix LG Monitor flashing green blue problem on Mac mini (Late 2014)

Hi guys,

I recently bought a 4K LG Monitor for my late 2014 mac mini and of course it is functioning in 4k but with 30Hz, so I got an active cable from mini displayport to hdmi 4k@60Hz. Before that I tried using SwitchResX to see if it helps (it didn't) so I got the cable. When first inserted the cable and turned on my mac mini the screen started flashing green and blue, I couldn’t take any action so turned it off. I thought it could be a conflict because of SwitchResX so i did my best to uninstall it... Surprise, after deleting all the SwitchResX files I could find the active cable worked miracles, I had 4K@60Hz. The miracle last up until today when I locked my screen and tried the unlock it... When trying to unlock the screen, when monitor woke up it started to flash again green, red, blue. The mac mini was working fine behind it, because it was playing music.

I went to the store got an active adaptor mini dp to hdmi, 8k hdmi cable this time, same thing is happening... when locking the screen and trying to unlock the monitor is goin crazy!!!

Please hep me, I need to figure it out!

mac mini (late 2014) 3GHz dual core i7/ 16GB ram/ Intel Iris 1536mb

screen: LG 27UL550P 4K

[Re-Titled by Moderator]

Mac mini, macOS 12.7

Posted on Mar 13, 2024 10:00 AM

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Answer 1

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den.thed

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90,916 points

Mar 15, 2024 8:10 AM in response to chriskilian

In addition to the excellent advise from hcsitas.

The Intel Iris GPU is pathetic and can not be upgraded or replaced.

Going from Mini DisplayPort to HDMI has always been flakey with those older Mini DisplayPort Mac's.

So once again, I suggest that you go HDMI to HDMI or... Mini DisplayPort to DisplayPort with that display.

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Answer 2

den.thed

Level 10

90,916 points

Mar 13, 2024 12:26 PM in response to chriskilian

OK sorry, I thought that you were going from the Mac mini's HDMI port to DisplayPort on the display.

I would test a Mini DisplayPort to DisplayPort cable instead of the Mini DisplayPort to HDMI adapter.

for example's > https://www.amazon.com/s?k=mini+displayport+to+displayport+4k&crid=GCEOR2290U27&sprefix=mini+displayport+to+displayport+4k%2Caps%2C133&ref=nb_sb_ss_ts-doa-p_1_34

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Answer 3

den.thed

Level 10

90,916 points

Mar 13, 2024 10:48 AM in response to chriskilian

Revisit the Late 2014 Mac mini "Video Support" spec's, at > Mac mini (Late 2014) - Technical Specifications

Then the LG spec's, at > https://www.lg.com/us/monitors/lg-27ul550-w-4k-uhd-led-monitor#pdp_specs

The optimal connection methods from the Late 2014 Mac mini to that LG display are:

1) a HDMI to HDMI cable @ 30Hz from the 2014 Mac mini's HDMI port.

2) a Mini DisplayPort to DisplayPort cable @ 2560x1600 from the 2014 Mac mini's TB/Mini DisplayPort.

The Late 2014 Mac mini's GPU spec's are limiting you from getting the full satisfaction from that LG display.

Plus I'm really surprised that the unsupported HDMI to DisplayPort connection even works at all.

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Answer 4

hcsitas

Level 6

13,964 points

Mar 15, 2024 7:16 AM in response to chriskilian

Explained perfectly, thank you.

Since both the Mac & OS are almost obsolete - there’s no possibility of a fix, unfortunately.

The good news is that your Mac startup is quick and snappy. So your best solution IMO is to avoid Lock Screen and shut the Mac to workaround this problem. Not the answer you’re seeking but that’s how I would resolve. Good luck!

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Answer 5

hcsitas

Level 6

13,964 points

Mar 13, 2024 10:19 AM in response to chriskilian

It’s not supported. 60 Hz over HDMI only and that too for 1080p. For higher resolutions, stick to 24/30 Hz max.

In short, you paid for not one but two LG HDMI ports, use them. Any other way is beyond adventurous (as you’ve found out already) - not worth the time or money.

All the best 😉

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Answer 6

chriskilian Author

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5 points

Mar 13, 2024 11:40 AM in response to hcsitas

it works well if you use one of these cables/adapters - https://www.amazon.com/DisplayPort-Adapter-Thunderbolt-Compatible-Projector/dp/B07ZNH35M5/ref=sr_1_4?crid=159L194QGK27D&dib=eyJ2IjoiMSJ9.ukxm-6cOZ5ifY9-YBHF0RHoadR-3m5v_DDA7J-nECQAe1-PBsuIyQCDKYELthoLENNdqByM6zDeHoNMaEc-5v4XYhHuLgBZIFJoQ9y1oHwJK17YWgt5f0rqwrCX7KT0NObFg6nleCToA7smJqVGtLC9Ug0LcdK0r6_v9F7M2EzSE5N9ZN-GFxfhTZchZY4EQVU7q1Laq55epcyfCZHdlJ3e9uJSPQSFLHYm01cmWl-jPsqh1Ewhm6U6s0ROJtRwFFUyH0OsDTO3L5gnrCeqb5rsiw-gqy1Q-MaBBIWY1teM.A7MRhMHU4AAxpz3-xt6c5f-8ts-4PptdH275c1hKuvk&dib_tag=se&keywords=displayport%2Bto%2Bhdmi%2B4k%2B60hz%2Bactive&qid=1710355007&s=electronics&sprefix=displayport%2Bto%2Bhdmi%2B4k%2B60hz%2Bactiv%2Celectronics%2C193&sr=1-4&th=1

My mac works well with this. the problem with the flashing display is when computer is locked and I try to log in again

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Answer 7

chriskilian Author

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Mar 15, 2024 7:24 AM in response to hcsitas

I understand! Thanks!

my mac is snappy because it has a ssd drive. I have a strong feeling that this is caused by SwitchResX, because i installed it previously buying the adaptor and when I inserted the adaptor for the first time it did exactly like in the video! I uninstalled switchresx and worked, but got that situation on logging out.

this is my studio mac, i got a lot of programs and plug-ins installed, it would be a great pain to have a clean install. Do you think that an installation from recovery mode would override the system files and can work?

thanks!

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Answer 8

chriskilian Author

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Mar 13, 2024 11:42 AM in response to den.thed

I will upload a video on YT and show what's exactly the problem! I feel you don't understand exactly the issue, presumably I didn’t explain myself too well.

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Answer 9

hcsitas

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Mar 13, 2024 1:08 PM in response to chriskilian

Try this setting:

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Answer 10

chriskilian Author

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Mar 15, 2024 6:49 AM in response to chriskilian

To be more explicit about the problem I attaches a YT link for a video I made! I hope this will explain - YT Video

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Answer 11

hcsitas

Level 6

13,964 points

Mar 15, 2024 7:30 AM in response to chriskilian

It might be but IMO, it’s less effort, less money (time = money) and more rewarding replacing your setup with a brand new mini. Wait it out until M3 comes out, can’t be too far away.

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How to fix LG Monitor flashing green blue problem on Mac mini (Late 2014)

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