LG 27UD69P-W display with 5K iMac problem

[gowanis]

Just bought the LG 27UD69P-W 4K display to add to my new 5K iMac. I am using a USB-c to displayport cable purchased from Amazon (cable has all good reviews). I have the display working, but when I boot, it doesn't come "on". Mac OS recognizes the display, but it seems I need to unplug from thunderbolt port, and then plug back in to get it to come on. Any ideas what might be wrong here?

I also want to add, that side by side, the iMac is significantly brighter. Is there a likely brightness issue with the LG, or am I just spoiled by how awesome the iMac 5K display is ?

 

[chscag]

Just a WAG here.... it sounds like the LG is sleeping until a video signal wakes it. Unplugging and then plugging the cable back in likely wakes it up. I would try another cable from a different manufacturer. Apple cables are expensive but they do work best.

 

[gowanis]

What cable would you recommend? I called my local Apple store before buying my current cable, and they had nothing to offer that is direct USB-C to Displayport. Also, any comment on the brightness issue?

 

[chscag]

I just looked up the specs on your monitor at the LG web site. The brightness difference is a no brainer. Your iMac screen is 500 nits while the LG is only 300 nits. Also the LG has HDMI and Displayport connections. Where are you getting the USB-c from? Your iMac output connections are TB (Displayport).

 

[gowanis]

The Thunderbolt 3 port on the iMac is compatible with USB-C. This is the cable I'm using:

https://www.amazon.com/gp/product/B074GVQBY2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

[chscag]

I still don't understand the use of that cable. Displayport to HDMI would seem to be a better choice and in fact might work better. However, that's up to you.

 

[gowanis]

Isn't is true that if you use HDMI, you can only get 30hz refresh instead of 60hz ?