External monitor doesn't wake up when iMac turns on

I recently bought an iMac 27, 3,4 GHz core i5, Retina 5k, late 2017, 8+8 Go ram memory, running on High Sierra 10.13.2. It is connected to two Acer G247HYL external displays through USB-C/HDMI connectors. When I turn on the iMac, the displays do not wake up. They don't appear in Preferences system/Monitors even if I click on Option to detect monitors. The only way to wake them up is by unplugging and replugging the HDMI connector, which is inconvenient. I have reseted the NVRAM (start in Option + Command + R + M), reinstalled the system, double check the connectors (which are brand new) and the displays (which worked well with my previous iMac 2011). Interestingly, the external displays wake up automatically when I restart the iMac. Any suggestion would be much appreciated. Thanks.

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Given the age of this machine,

I would call Apple Support and have them sort out the problem.

One question though. Where did you get the USB-C to HDMI adapters from?


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Wait, you need USB C to HDMI adapters?

I thought these machines had video connections or required Thunderbold displays?

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I believe Thunderbolt uses USB_C style connectors

on the iMac end.
This from the Tech Spec:
"Thunderbolt 3 digital video output
Native DisplayPort output over USB‑C
Thunderbolt 2, HDMI, DVI, and VGA output supported using adapters (sold separately)"
iMac picture shows two Thunderbolt ports, based on USB-C connectors.
"Two Thunderbolt 3 (USB-C) ports with support for:

Thunderbolt (up to 40 Gbps)
USB 3.1 Gen 2 (up to 10 Gbps)
Thunderbolt 2, HDMI, DVI, and VGA supported using adapters (sold separately)"

Merry Christmas Bob


Post was last edited on December 25, 2017 7:35 AM PST

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So are there Apple made adapters?

I run into so many adapters that just don't work.

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Yes, Apple make and sell a variety of adapters

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