Problems with 2nd monitor

[mikethebook]

I run a 2014 Mac Mini with an Acer V173 17" monitor through a Thunderbolt port using a Mini Display plug. But I've just bought a Dell 17" monitor with a hdmi VGA adaptor and turning on the computer with both plugged in causes flashing of the image on the main monitor. What is going on? Why would what is plugged into the hdmi port affect what's plugged into one of the Thunderbolt ports? Many thanks.

 

[appltech]

My thought is that because VGA adaptor. HDMI is a digital one; VGA - analog.
Check this thread for more details.

 

[mikethebook]

Thanks appltech. So I need to plug both VGA monitors into the Thunderbolt ports (there are two)?

 

[appltech]

According to that thread, this might be a solution

 

[Amethyst1]

But I've just bought a Dell 17" monitor with a hdmi VGA adaptor and turning on the computer with both plugged in causes flashing of the image on the main monitor.

What is showing on the second monitor when this happens? Nothing?
The Mac is probably trying to “identify” the second monitor (and failing) over and over again. That can cause all connected monitors to flash on macOS.
I’d also suggest using an active MiniDisplayPort-to-VGA adapter.

 

[mikethebook]

Thanks, guys for the confirmation. I've ordered a Mac MiniDisplay Port to VGA adapter.

 

[Amethyst1]

Can you list the model number of the Dell monitor? Does it only have a VGA input?