iMac (24-inch, Early 2009) External Monitor Issue

[KirbyThe1]

Hi All,

I have a iMac (24-inch, Early 2009) running Catalina 10.15.7 (19H2). I tested with multiple monitors - different manufacturers - sizes etc with the same results.

I connect any external monitor via the mini DP to HDMI results in the same problem. Both screens ( iMac and external ) flash the desktop after login but then gets kicked back to the logon screen. If I reboot iMac into safe mode, the external monitor work perfectly. I disable password for login - same result.

Is this a known issue / bug with an early 2009 running Catalina?

Thanks

 

[Fishrrman]

This is only "a guess", but if "safe mode" boots fine (to the finder) when "regular mode" does not, the problem is located in your user account.

Probably something with startup items, kexts, etc.

A way to confirm this:
Go to the "users & groups" preference pane.
Create a COMPLETELY NEW account. This is temporary and for testing purposes.
Give it administrative privileges and whatever name/password will do (remember, this is just a "test" account).

Once created, reboot.
Now, see if you can get to the login panel without problems.
If you can, see if you can log into the NEW account without problems.

IF you CAN log in and get to the finder, then this almost certainly points to something in your regular account that is the source of the problem.

The more difficult part becomes finding out just WHAT it is in your account that is causing the trouble...

 

[Nguyen Duc Hieu]

Hi All,

I have a iMac (24-inch, Early 2009) running Catalina 10.15.7 (19H2). I tested with multiple monitors - different manufacturers - sizes etc with the same results.

I connect any external monitor via the mini DP to HDMI results in the same problem. Both screens ( iMac and external ) flash the desktop after login but then gets kicked back to the logon screen. If I reboot iMac into safe mode, the external monitor work perfectly. I disable password for login - same result.

Is this a known issue / bug with an early 2009 running Catalina?

Thanks

Me, too. Both on mDP to HDMI, or mDP to D-SUB cable.
But I assume it's normal because we are using a patch to install Catalina to unsupported iMacs. Weird things happen in the patch. Probably the Legacy VGA part.
I stopped using the external display since then.

 

[KirbyThe1]

This is only "a guess", but if "safe mode" boots fine (to the finder) when "regular mode" does not, the problem is located in your user account.

Probably something with startup items, kexts, etc.

A way to confirm this:
Go to the "users & groups" preference pane.
Create a COMPLETELY NEW account. This is temporary and for testing purposes.
Give it administrative privileges and whatever name/password will do (remember, this is just a "test" account).

Once created, reboot.
Now, see if you can get to the login panel without problems.
If you can, see if you can log into the NEW account without problems.

IF you CAN log in and get to the finder, then this almost certainly points to something in your regular account that is the source of the problem.

This is only "a guess", but if "safe mode" boots fine (to the finder) when "regular mode" does not, the problem is located in your user account.

Probably something with startup items, kexts, etc.

A way to confirm this:
Go to the "users & groups" preference pane.
Create a COMPLETELY NEW account. This is temporary and for testing purposes.
Give it administrative privileges and whatever name/password will do (remember, this is just a "test" account).

Once created, reboot.
Now, see if you can get to the login panel without problems.
If you can, see if you can log into the NEW account without problems.

IF you CAN log in and get to the finder, then this almost certainly points to something in your regular account that is the source of the problem.
The more difficult part becomes finding out just WHAT it is in your account that is causing the trouble...

Thanks for the reply and what you said makes logical sense but that did not correct the issue.

 

[retta283]

That machine is lacking 100% complete graphics acceleration under Catalina right? If so that might explain why it freaks out with a second display. Same problem occurs using a 2006 MBP on Yosemite with more than one screen, full stopper.

 

[KirbyThe1]

Me, too. Both on mDP to HDMI, or mDP to D-SUB cable.
But I assume it's normal because we are using a patch to install Catalina to unsupported iMacs. Weird things happen in the patch. Probably the Legacy VGA part.
I stopped using the external display since then.

Thanks for the reply - that saves me the small expense of testing various adapters. I was not sure if the issue was related to Catalina or the patch but had a feeling it was due to the age of the iMac. Like I said all external displays work in safe mode- even tried USB/USB-C to mini HDMI to little external LCD - same problem - worked on in safe mode.

It almost seems there is something going on in the background as once i log in both IMac and external display seems to work for a second or 2 then go black for about 15 secs, then I get kicked back to login screen. Seems like its trying to do something with the resolution or its some security thing, but thanks for the info.

 

[KirbyThe1]

That machine is lacking 100% complete graphics acceleration under Catalina right? If so that might explain why it freaks out with a second display. Same problem occurs using a 2006 MBP on Yosemite with more than one screen, full stopper.

You are correct on the lack of graphics acceleration - weird thing is it works fine in safe mode - are you saying that graphic acceleration is disabled in safe mode ? If so then that's probably the issue

 

[Nguyen Duc Hieu]

If you really want to use the external display, switch back to El Capitan.
The external display works fine when the OS is El Capitan.

 

[krisb78]

Hi All,

I have a iMac (24-inch, Early 2009) running Catalina 10.15.7 (19H2). I tested with multiple monitors - different manufacturers - sizes etc with the same results.

I connect any external monitor via the mini DP to HDMI results in the same problem. Both screens ( iMac and external ) flash the desktop after login but then gets kicked back to the logon screen. If I reboot iMac into safe mode, the external monitor work perfectly. I disable password for login - same result.

Is this a known issue / bug with an early 2009 running Catalina?

Thanks

Hi,
I wonder if you have had any further progress with this issue? I have the same problem with an early 2009 (20") iMac patched to Catalina with the dos dude file. Everything else seems to work apart from the second screen (strange logout scenario too when the screen is switched on).

Cheers!

 

[Fishrrman]

OP wrote:
"You are correct on the lack of graphics acceleration - weird thing is it works fine in safe mode - are you saying that graphic acceleration is disabled in safe mode ?"

I believe that when you boot into safe mode, you boot into the integrated graphics and are NOT USING graphics acceleration. I could be wrong.

Having said that, if the iMac runs with an earlier version of the OS, but doesn't run under Catalina... the solution seems pretty clear to me... use "what works".

 

[Painkiller]

I had this problem as well with Catalina and the updated patches after the installation. Right after the installation I saw that my second monitor was working. Then i installed the updated patches and I had the same problem. So I just don’t install those patch updates. Just can’t tell what the patches were. Nightshift and another one. And probably one out of these two might cause the issue with the external screen...

 

[retroneo]

The solution is in this post:

#13,527

 

[Nguyen Duc Hieu]

The solution is in this post:

#13,527

Thank you for your info.
The solution described in that post is way above my understanding and capability.
Further more, my iMac 24" early 2009 is quite struggling with 1 monitor. adding another monitor may stress it too much and resulting in a sluggish machine.

 

[errorlog]

The solution is in this post:

#13,527

I don`t understand what "the solution" is.

My Penryn mid 2007 Imac 24 works really fine with Catalina 10.15.7 thanks to the dosdude1 patcher.

But I miss my external monitor.

I definitely need a step by step "solution".

Can you help me? Pleeeeeease?

 

[errorlog]

I think I found the problem today: my 2008 IMac 20 had the same problem after installing the "Backlight Control Patch".

Uninstalling the patch does not fix the problem. I had to reinstall my backup (Image of a fresh installation).

Hope it helps...

 

[Warmachine1213]

I think I found the problem today: my 2008 IMac 20 had the same problem after installing the "Backlight Control Patch".

Uninstalling the patch does not fix the problem. I had to reinstall my backup (Image of a fresh installation).

Hope it helps...

Hey sorry I’m having this same issue I’m a little confused on your solution. Did you do a clean install ? With out adding that patch ?

 

[BrendTM]

Run into kind of the same Problem when I installed Catalina (dos dude patcher) on my early 2009 IMac with a GT120.
I got an mini dp to HDMI Adapter, when I plug it into the mini dp with the Adapter already attached to the monitor it shows an video output on the external monitor for 2 seconds before my session crashes and Im stuck in the login screen.
While in login screen the second monitor still works, I can put the mouse over to it and it works normaly, but when I try to login with the screen attached it will always bring me to the login screen again.

In the Console I can see that WindowServer and LoginWindow have been crashed.

When I detach the external Monitor I can login normally.

I realy would like to use a second screen to use the Mac for Remote work.

Can someone confirm not applying patches after clean installation is fixing this problem?

EDIT:

I just freshly installed Catalina with the Bootstick created from the Catalina Patcher, after the Installation I skipped installing the Patch Updater Patches and disabled them.
My external Monitor is now running perfectly fine, so there must be an problem with the patches.
I can savely install the patches that I get from the System itself (Safari update ...).

 

[itsmesunny]

Hi Kirby,
I gave mine - iMac (24-inch, Early 2009) to someone. I updated.

How did you upgrade to Catalina, when this year iMac could only go to El Capitan?

 

[Amethyst1]

How did you upgrade to Catalina, when this year iMac could only go to El Capitan?

macOS Catalina Patcher

 

[itsmesunny]

macOS Catalina Patcher

Thanks.
I will check it out.