iMac boots to blank screen. I have run out of ideas…

[Happy Marsden]

I’ve a 21” mid-2011 iMac (12,1), running Ventura (via Open-Core Legacy Patcher). It worked fine for months. But two weeks ago, my iMac suddenly went black, while I was simply reading on the internet browser. I thought the display had died, but it didn’t. Nevertheless, I've been unable to get my system back to normal, ever since.

I’ve tried numerous different drives (HD and SSD), numerous macOS’s (from High Sierra to Sonoma), and different format types (“Journaled" on High Sierra, to “APFS" on the later OSes). Most of the time, it loads the Apple logo and progress bar, but then, stays on a blank screen (grey or black, depending on whether I’m using an OCLP EFI boot or a native Apple one).

However, for some unknown reason, it will run the drive with the Ventura OS that was installed (via OCLP) on my 2010 iMac 11,2. Even though it won’t load the Ventura desktop installed on the drive that was installed on my 2011 iMac! But OCLP requires that you patch the system for the Mac you are using it on. And as soon as I run the OCLP patcher on my 2011 iMac, it will go blank, after the boot screen.

There are 3 things that the OCLP patches, and one of them is “AMD Terascale 2” GPU. At first glance, it would seem that is the “problem patch”. Because if I leave the system unpatched, I cannot adjust brightness or use lower scaled resolutions on the iMac’s display.

The only other operating system that I was able to load on my 2011 iMac, was “Catalina”, installed via “Dosdude”’s patcher. However, same problem there, with the display. Can’t access brightness, can’t change from default resolution. Attempting to run the Dosude patcher results in the same issue afterward: I can no longer boot into the desktop, because — blank screen. (Even when attempting to boot into "safe mode").

It's even gone into a "reboot loop" sometimes, where it shuts down the computer, then restarts, infinitely. But thankfully, this occurred only on some types of installations I was trying. I can't do an "Internet Recovery" install either, even though I am connected via Ethernet. It starts out fine but then it goes blank and just won't ever complete.

I thought this was an “Open Core Legacy Patcher” issue, where somehow, the patch for the AMD Radeon GPU simply stopped working. But that can’t be it, because I installed a fresh copy of HIgh Sierra, which is native to my iMac, on a freshly Journal-formatted SSD. And though it may have worked on the first go, it gave the same result after reboots: a blank screen after the loading bar. Also, I can take the same drive that won't boot on the 2011 iMac, and it will boot and load the desktop, on the 2010 iMac.

I also thought the problem might stem from a corrupt EFI. But that can’t be, if the EFI firmware is written to a drive, and not a chip on the iMac itself, can it? The fact that it boots in error in every drive, would suggest that's it's not a drive issue, nor an OS issue.

I know it's not a RAM issue, as I've tried swapping out all the RAM modules.

I ran the Apple Diagnostic Test, which gave me error: 4SNS/1/40000000:TH00-9.000. Which is just a temperature sensor. Which is to be expected, as I swapped out the Apple HD for a non-Apple HD.

Finally…. I am considering the idea that the AMD Radeon HD6770M GPU’s firmware got somehow corrupted. But a search for firmware on AMD’s site for this GPU, shows only other operating systems supported… not Mac! And the reason I am looking at the GPU firmware as a possibility, is because...

a) the GPU itself must be okay, if it can sometimes load a desktop, even if it can only display at the default resolution.

b) When I tried to load Linux (Debian) “GParted” partition software off a USB flash drive plugged into my iMac, I couldn’t. But got this error message: “ERROR - Radeon kernel mode setting for R600 or later requires firmware installed. See — for information about missing firmware”.

Assuming the firmware for my iMac’s GPU somehow got erased… is it even possible to reinstall it?

Else… anyone have any ideas of how I might go about fixing this issue?

 

[DarkPremiumCho]

Surprisingly also 2 weeks ago I got a similar issue 🤔. I was frustrated after numerous attempts.

Until I downgraded the WhateverGreen.kext to version 1.6.5 and booting to blank screen is no more.

Hope this helps. If you are not familiar with kexts, try older versions of OCLP.

 

[Happy Marsden]

I am familiar with .kext files, as I did a "blessing"(?) in Terminal, to fix the blank screen problem, on a patched system that was using OCLP. This normally meant deleting the .kext files in Library/Extensions, save for two files ("HighPoint"-something). This did in fact work at solving the blank screen issue, and booting into the OS. But only sometimes, on some OS installations.

However, it didn't matter if I could boot into the OS, because I was still never able to do root patches on my system, via OCLP. Which for me, made the system unusable. Furthermore, the fact that I am unable to boot into the desktop on native OS installations that are not using OCLP, including the "High Sierra" internal HDD that used to work!, suggests that the issue goes beyond .kext files.

Nevertheless, I saw that my original internal High Sierra HDD had dozens of .kext files in its System/Library folder. Including many relating to the iMac's AMD Radeon GPU. But the OCLP installations I created, such as Ventura, always only 2 .kext files, or not much more than that. Those are the "HighPoint" .kext files, again. So I am going to try to find a way to copy all the .kext files from my internal High Sierra HDD install, over to another drive (using OCLP or not), and see if the problem results from missing AMD Radeon GPU driver (.kext) files. Especially when I see I am able to boot the drives on another iMac, without issue.

Though I still don't know why the internal High Sierra HDD that has all those .kext files, will no longer boot. Perhaps using OCLP on another drive, corrupted its EFI files or partition.

Today I created a USB installer for Snow Leopard, the iMac 2011's original OS. It would not boot the installer, and gave 3 beeps. But when I booted the USB flash drive on my older 2009 iMac, it booted into the Snow Leopard installer. 3 beeps apparently, is a firmware issue. So maybe that's a clue. But as far as I know, the mac doesn't have any built-in on-board firmware that is user replacable. It's all on the drives themselves.

 

[Nguyen Duc Hieu]

Let's go back to the officially support Mac OS High Sierra without OCLP to verify your statement that the "GPU must be okay".
You can either boot it with a High Sierra USB installer, or High Sierra pre-installed SSD.
If it can get you to the desktop graphic, then we can verify that your GPU is still OK.

Why I suggest the above test?
I had an iMac 2009 running HD4850. One day the iMac booted to 2/3 of the progression bar, then stuck there forever.
The issue was solved when I replaced the GPU with AMD Firepro M6100 and patching with OCLP.

I also got another iMac 2011 booted well to Yosemite, but hung up on High Sierra.
I also concluded that the HD6770m inside my iMac 2011 is half-dead.

 

[MacDownunder]

Yours does similar things to my daughters 2011 27". The splash screen loads and then when OS loads goes to blank screen. I bought a SH GPU but while was waiting cooked the original with heat gun as had nothing to lose. I actually didnt even have any fresh thermal pastes so had to kludge what was there put it back together after GPU cooled booted and hasnt missed a beat for over a month.
Now I know this is temporary and the other GPU is sitting waiting for that day - but you have zero to lose and only a few hours at worst of time.
YMMV but heck try it and see what happens

 

[Happy Marsden]

Nguyen Duc Hieu: I booted it with both my original High Sierra USB installer, and my pre-installed internal High Sierra (HDD) hard disk drive (Journaled format).... as mentioned, it gives me blank screen after the progress bar loading. I am only able to get into the desktop via a specific Ventura system (which uses OCLP), or a Catalina system (which uses DosDude patcher). I was also able to get my 2011 iMac to boot into and work inside Sonoma. This is the reason I said the GPU must be working, else I would not be able to ever see a MacOS desktop.

However, regardless of whether I'm using Open-Core Legacy Patcher or a DOSDude hack, and whether the OS is Catalina, Ventura or Sonoma, once I apply the root patches, the system loads to a blank screen. And if I don't apply the root patches, the display can't be changed from the default resolution - among other issues. This is why it appears to be more of a software issue (ie. firmware), than a hardware fault (ie. with the GPU).

As for why I can't get into the desktop on the original High Sierra HDD internal drive, I suspect that OCLP may have "corrupted" its EFI. It's data is still intact, thankfully. So I tried to copy the AMD Radeon GPU .kext files to an external SSD, to see if that is the problem. But $#! Apple won't allow me to copy my own files from one drive to the next! It locks the external drive and won't allow any permissions to be opened, even after checking 'Ignore all permissions'!


MacDownUnder: Not sure what you mean by you "cooked the GPU". Normally, that's done in a slow oven, not with a heat gun. Not sure how a heat gun would revive your daughter's ailing GPU?

 

[Nguyen Duc Hieu]

Nguyen Duc Hieu: I booted it with both my original High Sierra USB installer, and my pre-installed internal High Sierra (HDD) hard disk drive (Journaled format).... as mentioned, it gives me blank screen after the progress bar loading. I am only able to get into the desktop via a specific Ventura system (which uses OCLP), or a Catalina system (which uses DosDude patcher). I was also able to get my 2011 iMac to boot into and work inside Sonoma. This is the reason I said the GPU must be working, else I would not be able to ever see a MacOS desktop.

However, regardless of whether I'm using Open-Core Legacy Patcher or a DOSDude hack, and whether the OS is Catalina, Ventura or Sonoma, once I apply the root patches, the system loads to a blank screen. And if I don't apply the root patches, the display can't be changed from the default resolution - among other issues. This is why it appears to be more of a software issue (ie. firmware), than a hardware fault (ie. with the GPU).

As for why I can't get into the desktop on the original High Sierra HDD internal drive, I suspect that OCLP may have "corrupted" its EFI. It's data is still intact, thankfully. So I tried to copy the AMD Radeon GPU .kext files to an external SSD, to see if that is the problem. But $#! Apple won't allow me to copy my own files from one drive to the next! It locks the external drive and won't allow any permissions to be opened, even after checking 'Ignore all permissions'!


MacDownUnder: Not sure what you mean by you "cooked the GPU". Normally, that's done in a slow oven, not with a heat gun. Not sure how a heat gun would revive your daughter's ailing GPU?

Software approach:
Basically there are 3 places you can make changes to and see if it fix your problem
1. The EFI (firmware) chip on the logicboard (flashing EFI ROM)
2. The vBIOS chip on the GPU (flashing vBIOS). Yours is the stock GPU => not necessary.
3. The hidden EFI volume on the SSD (modified by OCLP)

So my previous suggestion was changing No 3. by using a clean USB installer or pre-installed disk to check whether the GPU can take heavy load.
And by "desktop screen" I mean after the lock-in screen, you can actually go into the Mac OS desktop screen with a menu bar, open "About this Mac" and finder, etc...

We normally call "the progress bar" as "boot screen" or "pre-boot configuration screen", this screen doesn't apply heavy load on the GPU.

Your description may result from 2 followings:
1. Wrong setting in the OCLP patch.
2. After boot screen, your iMac internal screen is displaying the extended window (gray and blur screen), while the log-in screen is on a ghost display => some glitches in the port setting (also probably from the OCLP errors)

A simple trick to solve (though not very high expectation) is to do a PRAM reset.

Hardware approach:
MacDownUnder suggestion actually worked for many other users, instead of exposing the whole MXM card to the oven heat, one can use the heat gun to apply heat only to the main GPU chip. With some flux applied on the edge of the GPU, it might reflow the broken solder joins and make your GPU work again. It might not work at all. I did send my HD 4850 to a repair shop for rebaking under their professional reflow station with worse result.
Reballing the GPU (replacing all of the solder connecting the GPU chip to the MXM card) is not a viable option.

 

[MacDownunder]

MacDownUnder: Not sure what you mean by you "cooked the GPU". Normally, that's done in a slow oven, not with a heat gun. Not sure how a heat gun would revive your daughter's ailing GPU?

The heat gun is a paint stripper so gets extremely hot and can focus heat on specific part/component. As I mentioned in my case the reflow worked and continues to do so - though for how long who knows.
I have also "baked" a MacBook Pro (circa 2004) motherboard with the dreaded NVVIDIA Gpu in oven at 250C and revived that as well (eons ago). Reflowing is a tried and true method but, and big but, is hit and miss - sometimes works some times doesn't, sometimes lasts for ages, sometime very short time. The OP basically has nothing to lose trying the methods mentioned including attempting to reflow the GPU Die.

More so if you have a second machine that can boot the drive from this will at least confirm the OS install is sound. I eliminated all that by booting the iMac from multiple external drives using various OS versions. I was able to remote in and control the desktop so I knew the OS had loaded. What is/was weird and this is what tripped me up too is I got the splash screen and then when OS finalises the screen went blank. In an iMac there is not the integrated GPU and discrete GPU like in some MacBook Pros so really have no explanation why (seemingly like you) the initial load screen shows as a dead/sick GPU is dead/sick irrespective of OS load point

 

[Happy Marsden]

Nguyen Duc Hieu: Thanks for your input. I've been wrestling with "software approach #3" for days. I've also considered the fact that if the EFI is on the drive, that might explain why one drive doesn't work. But not why 5 or 6 drives don't work, and boot to a blank screen. Nor does it explain why 2 drives (that have OCLP patched systems), and 1 that has a DosDude patched system, does boot into the desktop, repeatedly. And I presume that booting into the macOS desktop would be considered a "heavy load" for the GPU, as compared to the boot screen.

As for "clean USB installers", I have tried reinstalling the OS from a USB flash drive, using everything from Snow Leopard, to Catalina, Monterey, and Ventura. Nothing ultimately succeeded, of course. Even though "Snow Leopard", was actually the original OS for my 2011 iMac. But I could take the same USB flash drive with the Snow Leopard installer, plug it into my 2009 iMac, and instead of a blank screen, it boots the installer, just fine.

I have done innumerable PRAM / SMC etc. resets; including Apple's key combo, OCLP's NVRAM reset option, and pulling the plug for 10s, then waiting 5s to turn the unit back on.

Although I will consider the "solder reballing" option for the GPU in the future, I am not convinced the GPU itself is faulty. For the fact that I can reliably boot into the desktop of some installations, play YouTube videos etc. -- but with certain issues (such as no scaling options). Thus I am still focused on software-based solutions; such as firmware or driver corruption issues.

I did wonder (but didn't know) that there was also an on-board ROM chip that holds EFI firmware. Not sure how or if this can be flashed, but I did download an "EFI Combo Update" software from Apple, for my specific model (12,1). However, I am afraid to install it! Because I don't know if the installer allows you to specify the drive that you wish to install it to. And I can't install it via the desktop of the drive I wish to "fix", since I can't access that drive's desktop. And I don't want it to automatically install to the boot drive, as that will ruin that system (since the boot drive would be from a different iMac).

As for OCLP's root patches, I was careful to ensure that the default settings were not changed, before doing the root patching. That didn't matter, it always ruined the system, by causing the screen to go blank after startup, once the root patches were applied. I also then tried playing with the OCLP default configuration, to see if I can avoid the problem. e.g. I tried disabling SIP, model spoofing, using older versions, using latest versions, and all kinds of things to get the root patching to work. I never succeeded, of course. But none of this explains why root patching worked fine when I first installed OCLP on this very same system, with the very same OS (Ventura).

I am still looking at the idea that the kext files (in System/Library/Extensions folder), particularly those related to my iMac's AMD Radeon GPU, may be the cause of the problem. Each OS installation on each drive, seems to have different .kext files in the Library/Extensions folders. But trying to transfer those files from my original drive to my new drive via the desktop, in order to test the theory out, has so far proven to be impossible. Apple won't allow write permissions to my target drive. There may be a way to copy files from one drive to another in Terminal, but I haven't researched this yet....

 

[Happy Marsden]

SOLUTION: I have finally resolved the problem I raised, in this thread. I am leaving the solution here now, in case it helps future members, that might have a similar problem. First, the problem....

TO RECAP: On my mid-2011 21.5" iMac (AMD HD6750 Radeon GPU), I had what is to me, a very weird graphic processor (GPU) problem, that did not quite seem like a GPU problem. Although it started off looking like it was....

It all started when I was reading text, and all of a sudden, without clicking anything, the screen went black. It wasn't the screen saver, because it stayed black, until I rebooted. But the display sprang back to life after I rebooted, and never went black again.

However, from that point on, I was unable to boot into the OS. I'd get the apple logo and loading bar, and whether the progress bar had completed, or not completed, it would never boot into the login screen. Nevermind the desktop. The screen would usually be grey or black (depending on whether I was using an "OCLP" system or not). And it was no different in recovery mode - including the native internet recovery mode. Which, left my repair options mighty limited.

It went like this for every OS I tried, including the original High Sierra, on my original HD - (native to my iMac). And I tried many different installations. However, two OS's I tried did work, in that they booted into the desktop, at least. One of them was a Ventura installation, the other a Sonoma installation. Both were courtesy of "Open Core Legacy Patcher" (OCLP). Obviously, since those systems won't work otherwise, on my 2011 iMac.

But when I say they "worked", I just mean, they booted into the desktop - at default resolution (~1920 x 800?). Surely, I thought, it can't be a GPU problem, if it loads the desktop. GPU problems are, in my understanding, marked by symptoms like... a black screen, a green one, grey lines, jumping pixels, weird colors... etc. etc. There was none of that - ever. The only issue with the Ventura and Sonoma OCLP systems, was that they could not display any resolution other than the default. Plus, you could not adjust brightness, and bluetooth would turn off in two seconds, once turned on.

I'm aware that these are all problems you get before root patching your OCLP installation. So that would suggest the problem is simply with OCLP. However, I could not ever root patch the working systems. For once I root patched them, then I would get the problem described above: it would hang on the loading bar, or just before the login screen. I tried different (ie. older) versions of OCLP, different versions of the KDK root patching kit, etc. etc. Nothing worked.

The question remains: Why did those two systems "work", when every other OS installation, including other OCLP OS's, did not? As I outlined above in this thread, I suspected it had something to do with either the EFI, or more likely, ".kext" files....

As for the "EFI", I am not talking about the EFI written to the Mac's boot drive. Because the problem persisted over several different drive changes. So I thought there was a firmware 'burned' to a chip in the iMac's logic board, or its GPU firmware, that was overwritten, or somehow corrupted, by an OCLP install. However.... replacing such firmware, where it existed, proved to be impossible, for me. (Apple only offers EFI "updates" to iMac's of this vintage. Very specific to certain OS's, and all but useless).

As for the kexts, "OCLP" creates ".kext" files, particular to your system, that load on boot. But the Ventura system that worked on my 2011 iMac (12,1), was created on a 2010 iMac. So it had ".kext" files for a different GPU and a different iMac (11,2). And yet, it booted into the desktop, where the High Sierra drive, which had my iMac's original .kext files, did not. Nevertheless, I thought that if I could copy the .kext driver files from the original High Sierra system, over to an OCLP OS install, I could get everything to work.

But of course, Apple has contempt for its customers, so.... they made it nigh on impossible for me to copy the files from my original HD, to an external SSD drive. Locked me out of my own files, by telling me I didn't have "permission" to copy my own files, from my own drive, to my other own drive! And it would not even allow me to ignore the permissions status on the drive, despite having a checkbox just for that! So I never succeeded there....

I ended up "solving the problem", by buying another 2011 iMac! But don't worry, that's not the solution I am posting today! I still wanted to fix my original 2011 iMac. And so, the only last resort I felt I had open to me, indeed it had to be the last resort.... was to bake the GPU card! This was suggested in this thread by "Mac DownUnder".

(Well.... he used a heat gun. Some sources suggested against using a heat gun, because it's hard to control where the intense heat is directed. So I went with the simple bake option).

I baked the GPU as recommended, for 10 minutes at 400F. I was not feeling very confident about this, after seeing a video by Lou Rossman on YouTube, saying that reballing was "bullsh*t"! And even explaining why it isn't what people think, in some detail.

But.... going against Rossman's advice, after I baked the GPU, all of the above problems went away. So it actually was a GPU problem after all! In the end, I was able to install Sonoma, install the root patches successfully, get wifi working, bluetooth, brightness, and other than default resolutions.

Rossman says these fixes are only temporary, and might last no more than 3 months. I guess that remains to be seen. But I can say that after the fix, I ran Geekbench and Cinebench... which stress the GPU and CPU. Yet the computer did not run hot, and the GPU did not fail. So I am hopeful for now.

A long solution perhaps.... but this was a complicated problem!

 

[Nguyen Duc Hieu]

So in short,
1. The issue was in hardware: GPU
2. Your solution was rebaking the GPU.

To be clear: Reballing GPU is beyond user capability.
I would have disagreed with Louis Rossman, but I've seen too many Youtube videos about graphic card repairing jobs. So I agree with him in general.
For iMac 2009~2011 MXM graphic card, if rebaking works, then reballing the GPU chip works better (last longer). But reballing at a professional repair shop will cost more than buying another 2nd better card to upgrade.

 

[Happy Marsden]

So in short,
1. The issue was in hardware: GPU
2. Your solution was rebaking the GPU.

To be clear: Reballing GPU is beyond user capability.
I would have disagreed with Louis Rossman, but I've seen too many Youtube videos about graphic card repairing jobs. So I agree with him in general.
For iMac 2009~2011 MXM graphic card, if rebaking works, then reballing the GPU chip works better (last longer). But reballing at a professional repair shop will cost more than buying another 2nd better card to upgrade.

Yes, correct, the issue was in hardware. Not having much experience with this, I assumed "reballing" was another term for baking a card or board. Especially after Rossman explained how it melts the many tiny balls of solder. But maybe he was referring to the heat gun method, I don't recall. I do recall him saying that if you bought a reballed GPU from a professional repair shop, it'll be dead after 90 days. Obviously, to people who have nothing to lose, by losing the GPU... I think it's definitely worth a shot.

 

[Nguyen Duc Hieu]

Yes, correct, the issue was in hardware. Not having much experience with this, I assumed "reballing" was another term for baking a card or board. Especially after Rossman explained how it melts the many tiny balls of solder. But maybe he was referring to the heat gun method, I don't recall. I do recall him saying that if you bought a reballed GPU from a professional repair shop, it'll be dead after 90 days. Obviously, to people who have nothing to lose, by losing the GPU... I think it's definitely worth a shot.

By "reballing", I meant the job of removing the GPU chip, replace all solder joints with new solder. Some shop use solder balls (thus the name reballing), some other use solder paste. Louis Rossman did the reballing many times in his videos on the Macbook, sometimes even replacing the GPU chips itself.

To pull this, you will need head gun, GPU stencil (to match with the GPU chip), microscope (to verify all the balls are in place) and rework station and a lot of experience. That's why it's not for common users.
If the issue is not about the broken solder, but about the GPU chip, or the VRAM, or the VRM that regulate electric current provided to the GPU chip, then reballing won't help.
iMac 2009 ~ 2011 has bad solder from the begining, so reballing fix the solder issue once and for all. It can't prevent the card from failing elsewhere.

 

[MacDownunder]

I ended up "solving the problem", by buying another 2011 iMac! But don't worry, that's not the solution I am posting today! I still wanted to fix my original 2011 iMac. And so, the only last resort I felt I had open to me, indeed it had to be the last resort.... was to bake the GPU card! This was suggested in this thread by "Mac DownUnder".

(Well.... he used a heat gun. Some sources suggested against using a heat gun, because it's hard to control where the intense heat is directed. So I went with the simple bake option).

Glad it worked, albeit probably only for a period of time. I would have baked it too but my wife wasnt too keen on electronics in the family oven thats only reason I used the heat gun, that and i'd ordered a SH GPU as well so if I killed it no loss.

Having said that I still havent had to replace the "cooked" GPU yet, now a couple months into "fix" so I guess the warranty has expired