External monitor recognizes MacBook but not iMac. Any ideas?

[Zethos]

I have an AOC i2353Ph which I use as a 2nd monitor with a iMac. It’s connected with using HDMI with a thunderbolt adapter. When the AOC is unplugged it no longer recognizes the iMac signal and says “no signal”. I then have to get out an old 2007 MacBook and connect it to the AOC though the same HDMI cable but with a mini dvi adapter. The monitor recognizes it and I unplug it and hook it back up to my iMac and it then recognizes it.

Any idea why this would happen?

 

[Fishrrman]

What "input alternatives" do you have on the display?

It looks to me (from looking at AOC's product page) that it has VGA, DVI, and HDMI?
Is this correct?

I would suggest you try some other connection configurations.

You might look into a MiniDisplayPort (iMac end) to VGA (display end) cable.
Some folks might say that you shouldn't be using VGA (which is analog) on a display capable of digital input, but "the proof is in the viewing".

If you try this, and the display looks good, and it works consistently, it might be the way to go...