I am a french Canadian from Quebec, so sorry if my english isn't that good.
I own a 2017 iMac 21.5 inch, A1418 MNDY2LL/A model.
I've recently got an blackscreen problem. The issue occurs on a strange way.
When I say blackscreen, I mean that nothing is responding on the iMac and the screen is black. Even the 10 second reset with the power button doesn't work. I have to unplug it.
When the iMac is freshly running after a day off, it can take about 3 to 4 hours before getting a first blackscreen. After getting it, and a complete reboot, the next one will occur about an hour after. After it, it become really unstable and the blackscreen can occur almost any time.
I tought it could be the HDD that had a problem, so I changed it for a brand new SSD HDD. But the blackscreen still comes during the download page of the iOS at the installation setup page. So I guess the HDD wasn't the problem.
So now, I am turning over forum to see if any of you could have an idea, before putting the iMac for sales for parts.
Any advice would be welcome.