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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Desktops > iMac boots but without apple logo

iMac boots but without apple logo
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Doc HM
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Jun 22, 2020, 09:03 AM
 
Any thoughts...

Got a 2009 27in that I replaced the graphics card in. Couldn't find the stock card so put in one from a 2010 which should work.
And indeed it does but...
On startup it chimes but the screen stays black. After a while it flicks to a blank grey screen then loads up the login window just fine.
I rest the PRAM etc on it but no change. If I connect an external monitor it displays the apple logo and startup bar on the external screen but not the main one.

Any ideas?
ta muchly
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reader50
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Jun 22, 2020, 02:20 PM
 
Any chance the donor card is a flashed PC card, rather than an original? A poor flash job could explain that.

I use dual monitors at home, and macOS tends to display the apple logo on the menu-bar screen. With external added as extended desktop, drag the menu bar around, make sure it's on the internal display. Shut down and reboot. See if it takes the hint. If it does, you can remove the external. Alternatively, you could attach the external and set mirror mode. Reboot and see if it's fixed.
     
Doc HM  (op)
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Jun 22, 2020, 05:50 PM
 
Originally Posted by reader50 View Post
Any chance the donor card is a flashed PC card, rather than an original? A poor flash job could explain that.

I use dual monitors at home, and macOS tends to display the apple logo on the menu-bar screen. With external added as extended desktop, drag the menu bar around, make sure it's on the internal display. Shut down and reboot. See if it takes the hint. If it does, you can remove the external. Alternatively, you could attach the external and set mirror mode. Reboot and see if it's fixed.
I'm leaning towards that myself. I might have to try to refresh it and see.
I've updated the Mac to High Sierra, reset the PRAM and NVRAM etc but its still doing it. If I boot from an external drive it does the same although it displayed the apple logo happily when the OS was updating.

Its an HD4670 so I guess I'll see what I can dig up on refreshing it.
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Waragainstsleep
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Jun 30, 2020, 11:47 PM
 
I don't think you necessarily have to flash a PC card to get that behaviour. Isn't that exactly how stock PCI-E GPUs behave in Mac Pro towers?
I have plenty of more important things to do, if only I could bring myself to do them....
     
reader50
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Jun 30, 2020, 11:58 PM
 
PC graphics cards (with rare exceptions) remain blank during boot. On all monitors. Until late in the boot process, when the high-level drivers finish loading.

Doc's iMac shows boot graphics. Apple logo and progress bar, but only on an external monitor. Not the internal one. That's distinctly weird. The internal comes to life later when the high-level drivers load.

A) It could be a Mac card with something off about it, like a bad flash.
B) OpenCore may be installed on that iMac (old card might have been a PC card). OpenCore is handling the boot graphics, but is not seeing the internal display for some reason.

The way to check if OpenCore is installed is to load the EFI partition of the built-in drive. Then see if there is an /OC/ subdirectory.

Use Disk Utility to find the disk number "X" of the internal drive. Then in Terminal:

sudo diskutil mount /dev/diskXs1 (substitute the actual disk number for "X")

Check the newly mounted EFI volume: /EFI/EFI/OC/(assorted files & folders) <- OpenCore is present.
     
Waragainstsleep
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Jul 1, 2020, 07:19 AM
 
He said black screen no logo then login window. Isn't that expected behaviour from PC card? The model does match the 2010 iMac he pulled it from though which is something of a coincidence.
I have plenty of more important things to do, if only I could bring myself to do them....
     
Doc HM  (op)
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Jul 4, 2020, 06:01 PM
 
Swapped the car out for another HD4670 and it all worked fine. So either a duff flash or just plain duff card.
Thanks for the helpful input though. I shall remember the OC stuff for next time.
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ghporter
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Jul 4, 2020, 07:04 PM
 
Congratulations on the fix. That sort of thing is awfully frustrating. “This is the right part, why doesn’t it work?” Yeah, I’ve said that a LOT.

It may be worth your time to try to flash the non-working card. If it was loaded with PC firmware and it successfully flashes with Mac firmware, you have a working Mac card. If you can’t flash it at all, it’s probably borked.

Glenn -----OTR/L, MOT, Tx
     
   
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