DisplayPort monitor unreliably waking from sleep  

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psonice
(@psonice)
Estimable Member
Joined: 12 months ago
Posts: 113
April 5, 2018 9:27 pm  

A little off topic here, as this happens with or without eGPU, but it's super annoying. I have an external 4K display connected via DisplayPort. It works great, except when waking from sleep. What happens:

Maybe 50% of the time, I'll wake my mac, and within a couple of seconds the external display will wake up. Everything works fine. 

Around 45% of the time, the mac display turns on, the external doesn't. Then, the mac display turns on and off every couple of seconds. Usually after a couple of cycles the external display finally turns on, and back to normal. Sometimes it doesn't, and it just cycles forever unless I turn the external screen off and on, then it picks it up.

The other 5%, the mac screen turns on and off a few times, then stays black. Nothing restores it, I have to power off.

Anyone else have this? Any suggestions for anything that might help?

Equipment: Late 2014 5K iMac (TB2) with 10.3.3, Acer CB240HYK 4K monitor plugged into an Nvidia 1080TI eGPU, but as said the same happens with a mini-DisplayPort cable connected direct to the mac.

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mac_editor
(@mac_editor)
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Joined: 2 years ago
Posts: 1596
April 5, 2018 9:35 pm  

Try SMC reset and ensure connections are tight - going on a limb here. This is a known problem with macOS High Sierra and is intermittent. 

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psonice
(@psonice)
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Joined: 12 months ago
Posts: 113
April 5, 2018 9:40 pm  

Thanks, I'll try the SMC reset when I reboot next. It is intermittent, and actually it does get noticeably worse the longer the mac has been up.

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ikir
 ikir
(@ikir)
Prominent Member
Joined: 2 years ago
Posts: 756
April 5, 2018 10:59 pm  

Have you tried select DisplayPort 1.2 protocol from Display internal options?

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psonice
(@psonice)
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Joined: 12 months ago
Posts: 113
April 6, 2018 8:00 am  

It's set to 1.2 on the monitor (that was needed to get 4k60 working if i remember right), is there a similar setting somewhere on the Mac? I haven't come across anything, but then i've recently used the BlueTooth explorer (unrelated problems on another machine) and was pretty surprised at how deep the settings Apple provide go there.

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psonice
(@psonice)
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Joined: 12 months ago
Posts: 113
April 6, 2018 11:17 am  

Just found a dual link DVI cable, tried that... seems to cure the issue, at the expense of 60hz. 30hz is more annoying than the unreliable connection unfortunately! 

Haven't rebooted to reset SMC yet.

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psonice
(@psonice)
Estimable Member
Joined: 12 months ago
Posts: 113
April 8, 2018 7:48 am  

Tried SMC reset, have put machine to sleep and woken it enough times to get a feel... and it's not perfect but does seem a whole lot better. So thanks for the suggestion @mac_editor, that might have done it!

I'll update this thread if it plays up again. Hopefully it'll be helpful if somebody else has this issue.

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