No sound on 27 inch iMac Mid 2011 running Windows 8.1 on Botcamp

Does your built-in Optical drive function properly?

amytom12 wrote:

And oh, I forgot to mention. When I was installing Windows 8.1, I got a MBR table error and something about EFI's and GPT. I looked on YouTube and this guy said to go to terminal on my mac side and put some codes in. I don't know if this effects the sound.

Yes, it does. If you do not use the internal Optical drive and a DVD (or CD) to install Windows on your specific model and instead use a USB (or manually choose) EFI boot, the Audio devices are not exposed correctly. This is indicated by the current BIOS Mode being UEFI. On your specific 2011 model, it should be Legacy (or BIOS).

The only method to switch to BIOS mode, is to remove the current installation using Remove Windows from your Mac - Apple Support and then use a DVD in the Optical drive to install W8.1. The 'code' you were asked to input in Terminal removed the MBR, forcing a UEFI installation, and causing the Audio to malfunction.

Do not use the first option - Create. Your Mac only properly supports Download and Install.

Download will not provide the correct drivers. You will need to find the appropriate drivers from Install Windows 7 on your Mac using Boot Camp - Apple Support for your specific model.

The only useful option is the Install, and using a DVD, not a USB.

Your MD5 is correct. Disconnect all external storage. Can you run a SMC and NVRAM Reset?

How to reset the System Management Controller (SMC) on your Mac - Apple Support

How to reset NVRAM on your Mac - Apple Support

Now insert your DVD and run BCA and click on the Install option.

You need to wait for partitioning to be complete.

Then you need to enter the commands in GDisk as shown in Re: No sound on 27 inch iMac Mid 2011 running Windows 8.1 on Botcamp as shown on page 7 of this discussion.

Once these two steps are complete, then you need to post the output of each of the following commands.

sudo gpt -vv -r show /dev/disk0

sudo fdisk /dev/disk0

Do you have the USB flash drive on which you downloaded the W8.1 drivers? If you did not, you can download it from Boot Camp Support Software 5.1.5621 on the Windows and run setup.exe from the Bootcamp folder.

Install GPT Fdisk (aka gdisk) from GPT fdisk download | SourceForge.net. If you are on High Sierra, you will also need to disable SIP by booting in Local Recovery (Command+R) and running

csrutil status

csrutil disable

csrutil status

If it shows 'disabled', boot normally and rebuild MBR to match the new GPT information thus resetting the Hybrid MBR. Use defaults for other questions (like partition codes). The only values that need modifications are the Boot flags and step 10. Accept all other defaults that Gdisk offers. Please see thesample Q&A as an example. These steps can be repeated if you make a mistake before you get to Step 12, otherwise start from Step 1 for these steps. Step 6 has numbers which are typed with a space between the numbers. Please see the sample Q&A before you execute these steps.

1. Sudo gdisk /dev/rdisk0
2. P (Print list of parts)
3. R (Recover)
4. O (print current Hybrid MBR)
5. H (chooses Hybrid)
6. Partitions numbers to be hybridized: 2 3 4
7. Y (Good for GRUB question)
8. N (part 2 boot flag)
9. N (part 3 boot flag)
10. Y (part 4 boot flag make NTFS bootable partition)
11. O (print current Hybrid MBR)
12. W (Write the new MBR)
13. Y (Yes! write the new MBR)
14. Reboot

Here is sample Q&A for this section. Please notice the Press Enter/Return.

Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): Y

Creating entry for GPT partition #2 (MBR partition #2)

Enter an MBR hex code (default AF): Press Enter/Return

Set the bootable flag? (Y/N): N

Creating entry for GPT partition #3 (MBR partition #3)

Enter an MBR hex code (default AB): Press Enter/Return

Set the bootable flag? (Y/N): N

Creating entry for GPT partition #4 (MBR partition #4)

Enter an MBR hex code (default 07): Press Enter/Return

Set the bootable flag? (Y/N): Y

You do not need W10 to get sound out of your 2011 iMac. W7/W8.1 work very well. Can you check the setting of BIOS Mode if you run msinfo32 from the Start -> Run command? If it is 'UEFI', your sound will not work. You need to ensure your Windows is installed using legacy BIOS mode, which is the BC Assistant default for your model.

What is the macOS version on your iMac? High Sierra has some issues in this area.

You do not need to boot into BIOS because Macs do not have a user interface for BIOS or UEFI. The installation method determines the type of installation. The msinfo32 command should provide the current type. It can be changed by re-installing Windows, provided some prerequisites (a MBR and the legacy BIOS boot is used) are setup correctly.

On a 2011 Mac, the default is BIOS, if you use the built-in Optical drive to install Windows.

Yes. You may want to use a DVD-R SL blank disc and get the ISO from Download Windows 8.1 Disc Image (ISO File) and burn it to the blank disc. Ti burn the Iso to blank disc, right-click on the downloaded ISO, choose Burn, expand the dialog box, and choose the Verify and Mount options and the lowest Burn rate supported by your media.

Run BCA, and you should only see two options - Download and Install. Insert the DVD, uncheck the Download box, and check the Install option, partition your disk and follow the prompts.

If you get an error message, please post a screen shot of the error, if possible.