Issues with Internal Display after Connecting Firewire for first Time

[NT1911PB]

Hello Mac community. Please don't stone me immediately if I don't get through completely or post this incorrectly in the forum.

About my problem:

I got several Macs as a joke. All from 2009 to 2011

Now I have a 2011 with 21.5 where the display doesn't work with the backlight. To test whether it even has an image output, I got a Firewire?! adapter bought to HDMI. Now I thought since the image output was black (i.e. no display, the monitor didn't turn on!) I'd better test it on the large 27" iMac from 2011.

Yes... That was a stupid mistake..

Now I have the problem that when I switch off the iMac 27 and want to start it again, I have to plug and unplug the Firewire HDMI adapter several times until it somehow and somehow notices that the iMac has an internal screen. The internal screen of the Mac stays black - only after plugging or unplugging this HDMI adapter a few times does the MAC realize AHHHHH THERE IS AN INTERNAL SCREEN

to the Mac:

2011 12.2
i7 2600
32GB
6970 1GB
2x 512GB SATA
Mac OS Ventura (With OpenCore)

As I said, I apologize if this is in the wrong thread - only the Mac always started normally and with the internal display. But since I stupidly tried out this HDMI adapter, the internal screen only starts in a detour.

I would like to thank you in advance for your answers!!!

 

[PaulD-UK]

You need to answer some questions about your computer arrangement.

Do you have another computer monitor that has an HDMI input?

Did you connect your 'bought to HDMI' adapter to this monitor?

What adapter is this? Is it a MiniDisplayPort to HDMI adapter?

If it is that, then did you plug it into a Thunderbolt port on your iMac?

Do you know the difference between the iMac's FireWire 800 port (one), and the iMac's Thunderbolt ports (one on 21.5" iMac, two on 27" iMac).

The Firewire port is NOT for connecting monitors, only HDs or audio interfaces.

If you did all this on the 27" iMac, then reconnect the HDMI adapter and monitor to the iMac, and boot the iMac so you get both screens working.
Then:
Go to the Apple Menu , click on System Preferences, then Displays, then select Display Mirroring.

Now you can shut the iMac down, and remove the adapter.
Then try starting the iMac again (with no HDMI adapter).
Do that help your problem?

 

[NT1911PB]

Oh yeah...sorry!!

I don't mean Firewire...

Thunderbolt is the connection.

The product was advertised on Amazon as working with Macs from 2009 - 2011 and the 21.5 and 27 inch.

Well, that's what it does. But the problem is that the internal monitor was deactivated somehow.

But I'll try the procedure described right away.