Yes it is what I did. I booted on my usb key "Opencore" and I was able to download the update via the system update (normal way). After the download (3.2GB), the iMac did a restart and until this step I was this black screen.
Did you put this option in your Opencore config.plist?
No, I didn't changed something. I used the same USB key like for upgrading BS from the beta 6 to beta 10.
I was able to check this (with my second Mac which is a MacBook Air) and in the config.plist of my USB key, the "run-efi-updater" is set to no
Ok, did you made, by chance, a backup of your iMac bootrom that you could reflash?. Because if your not able to boot on your old system that worked before, if your not able to boot from an installer USB flash drive, i feel that a firmware update could have corrupted your bootrom when installing Big Sur Update, even if you had run-efi-updater set to No. We are talking about beta software (Big Sur) and Opencore which is Beta too (booting a beta software). I hope, i am wrong.
I understand what you mean and unfortunately I don't have a backup :-(. I will try to find a solution if it exists and any idea is welcome.
The bootrom on a mac is unique because it contains the mac serial number. One computer, one bootrom.
Unfortunately no but maybe it is not expensive. Nevertheless thank you for your help.
Do you know how to reflash a bootrom on an iMac? Thank you
May be you can try to buy a Mac efi bootrom, read it and then flash back to your Mac with a programmer clip.
www.macunlocks.com
It seems it could be a good practice to make a bootrom backup before trying to install Big Sur on unsupported (i)Macs, just in case. To be able to flash back the bootrom with a clip.
hi i did this for various models of apple. the key is that the bootrom should be exact model. i.e. MBA5,2 for MBA5,2 not MBA5,1. I ended up buying a cable to plug into the SPI and restore firmware from the other working boards. after reflashing it i found out the logic board was actually broken not the firmware. it just showed up the problem by stressing it out with many installs of big sur. so they problem wasn't big sur but actually a logic board that slowly went bad. symptoms before dying were losing the serial number, and not connecting thunderbolt ports etc. frankly it was ali POS board that cost 125$. i bought 10 boards and one was POS. its pretty good odds. do check the price of the flash cables SPI for your model and compare them to the cost of the firmware chip that is exact model. understand also from 2012 models later the firmware chips are surface mount not easy to access the pins so you will need a hair dryer heat gun which costs about 20$ amazon. so they best way is to get a cheap SPI cable from korea (ebay) if there is one for your model. mine cost 50$ for macbook SPI. cool little connector. so do weigh the cost of a used logic board vs all the firmware route and decide which one you want to challenge. in the end i spent 100$ of chips and cable vs $150 for a new logic (alibaba). i learned a lot about so it was an investment in education. good luck!May be you can try to buy a Mac efi bootrom, read it and then flash back to your Mac with a programmer clip.
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These Apple BIOS EFI firmware chips are also sold in eBay & AliExpress, but often very costly, with the cheapest around $20-30.
lower pitch sounds like a voltage problem on the board. i have over 10 various macs and the pitch has always stayed the same.
This post is now out of date, please refer to the first post in this thread for up-to-date info
Complete guide on how to flash your iMac's boot rom and 765m/770m/780m gpu in order to get boot screen and the cards working with both MacOs and Windows:
Please others chime in if I'm incorrect with any of this.
This assumes you either already have Windows installed, or you have the ability to install Windows.
Some of this is how I would go about doing it, as with most things there's other ways and it pretty much comes down to what you're comfortable with.
- Setup and test screensharing on macOS just incase
- Disable SIP https://www.remorecover.com/blog/how-to-disable-system-integrity-protection-in-high-sierra
- Backup your rom with dosdudes' romtool http://dosdude1.com/apps/ (make multiple attempts and compare them against each other per FlorisVN's advise
)
2011 iMac Graphics Card Upgrade
no problem. perhaps Nick will make a rom for these quadro cards someday, let's hope. And if not it is possible to install a GTX765m inside a 21,5" iMac, i would personally not reccomend it in the first place. But others have done it, and it is possible.. If Nick, or anyone else felt inclined...forums.macrumors.com
- Download and unzip Nick's beta files https://forums.macrumors.com/attachments/kepler-beta2-zip.856644/ - put it on a usb drive
- Prepare the new bootrom as per:
with UEFITool https://github.com/LongSoft/UEFITool/releases/download/0.26.0/UEFITool_0.26.0_mac.zip- Install Windows via bootcamp, set up Teamviewer, enable auto-login on Windows and set Teamviewer to start on login. Set a Teamviewer password and do a few tests to see if you can remote in on another machine without touching the iMac
- Download and unzip NVFlash https://www.techpowerup.com/download/nvidia-nvflash/ - put it on a usb drive
- Put Nick's bios files in the same folder as NVFlash
- Install the new card - if it's a Alienware/Dell it should work fine in macOS
- Reboot to Windows by selecting Startup Disk in system preferences in macOS
- Remote in with Teamviewer
- Run nvflash from command prompt as admin - eg nvflash -6 765M_256K.rom
- You should then restart to Windows and it'll work - you'll just need to install the NVidia drivers
- Watch this video so you have an understanding of how to use flashrom and the CH341
- Switch to another machine (I used my macbook).
- Download Virtual Box https://www.virtualbox.org/ and Ubuntu https://ubuntu.com/download/desktop/thank-you?version=18.04.3&architecture=amd64
- Install Ubuntu, connect the CH341 and assign it to VirtualBox
- Run Ubuntu
- Open terminal and run "sudo apt-get install flashrom"
- Run "lsusb" to see if the CH341 is there - if not double check if it's setup correctly with VirtualBox
- If all good connect the CH341 to the eeprom on the iMac per https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/page-106#post-27689935
- Run "sudo flashrom --programmer ch341a_spi -r test.bin" to verify it's connected correctly.
- If it worked fine, flash the rom you created with UEFITool to the iMac "sudo flashrom --programmer ch341a_spi -w the-rom-you-created.rom"
- If that all went well you should be able to boot to a fancy new bootscreen
Edit: updated with correct version of UEFITool
This post is now out of date, please refer to the first post in this thread for up-to-date info
You will find the infos you need in these posts.
I had the exact same symptom with an MBP. I fixed it by disassembling and disconnecting the battery for some seconds. I also did the 'press and hold power button for five seconds' step here: https://support.apple.com/en-gb/HT201295. So just to double-check, you've definitely done the 'disconnect power and the press and hold power button' steps from there? However, if it has given you an incompatible firmware upgrade (I think I was basically lucky that my MBP is new enough to be compatible with the incorrect firmware upgrade which is applied by the latest OTA update, because the spoofing unfortunately says your machine can accept it) then yes, you may looking at finding out out how to reinstall your machine's firmware. :-(
here is the link for the schematic (logical roadmap of the motherboard) of the imac 2012. model number is called 820-3302A for reference. https://drive.google.com/open?id=1nN3XjDiE5bXgwGwWp6bFc-mVzcQ-g413
Until the real help gets here, tell us what version of micropatcher you are using. Also since it looks like you got at least past the first phase of the install sequence, tell us what step the install shows the failure. Lastly, can you write out the exact terminal commands you used in preparing and patching the installer? Thanks.
