MP 1,1-5,1 (Close please) I want to downgrade from Mojave back to El Capitan

[K2000]

I have a 2009 cMP 4,1 that was successfully flashed to 5,1 about a year ago. The machine was stable for about a year running El Capitan, then the CPUs shorted and the power supply failed a few months ago. So I put the original CPUs back in.

El Capitan worked fine except Safari performance was still really bad on certain websites, and I was curious to see if there would be general performance improvements with an upgraded OS. Mojave was my limit because I'm using Adobe Creative Suite 6 and there are reported CS6 issues beyond Mojave. I was able to update OS by disabling SIP and using the standard downloads from the Apple support page, updating each OS in sequence. I didn't use a bootable USB drive to upgrade.

However, in Mojave I have other software and plug-in conflicts, audio is horribly noisy in Mojave with the original 4,1 CPUs, and I've already had crashes in the first two days. So I want to go back to El Capitan if possible.

My question is can I revert back to El Capitan the same way I upgraded, step by step, without using a USB boot drive? I don't have a 16GB USB drive, as the instructions require. Could I use Recovery mode or just disable SIP again and re-install the OS sequence in reverse, using the standard Apple installers? Can I go backwards the same way I went forward: Mojave to High Sierra to Sierra to El Capitan? I backed up using Time Machine before I started the OS updates, and at every new OS I backed up again. So I should be able to install the files on my hard drive in the original format. (I assume Time Machine will not update an OS).

I'm kind of a noob. I need this Mac to be stable, more than I need it to be fast. Trying to research this, some of the info doesn't seem to apply to cMP. If the USB boot drive wasn't needed to upgrade, would i still need it to downgrade? Thanks.

 

[tsialex]

View attachment 1742794
I have a 2009 cMP 4,1 that was successfully flashed to 5,1 about a year ago. The machine was stable for about a year running El Capitan, then the CPUs shorted and the power supply failed a few months ago. So I put the original CPUs back in.

El Capitan worked fine except Safari performance was still really bad on certain websites, and I was curious to see if there would be general performance improvements with an upgraded OS. Mojave was my limit because I'm using Adobe Creative Suite 6 and there are reported CS6 issues beyond Mojave. I was able to update OS by disabling SIP and using the standard downloads from the Apple support page, updating each OS in sequence. I didn't use a bootable USB drive to upgrade.

However, in Mojave I have other software and plug-in conflicts, audio is horribly noisy in Mojave with the original 4,1 CPUs, and I've already had crashes in the first two days. So I want to go back to El Capitan if possible.

My question is can I revert back to El Capitan the same way I upgraded, step by step, without using a USB boot drive? I don't have a 16GB USB drive, as the instructions require. Could I use Recovery mode or just disable SIP again and re-install the OS sequence in reverse, using the standard Apple installers? Can I go backwards the same way I went forward: Mojave to High Sierra to Sierra to El Capitan? I backed up using Time Machine before I started the OS updates, and at every new OS I backed up again. So I should be able to install the files on my hard drive in the original format. (I assume Time Machine will not update an OS).

I'm kind of a noob. I need this Mac to be stable, more than I need it to be fast. Trying to research this, some of the info doesn't seem to apply to cMP. If the USB boot drive wasn't needed to upgrade, would i still need it to downgrade? Thanks.

You can downgrade if your have a TimeMachine, than you can go back to that image, but not successively. If you don't have a clone from your El Capitan install, you will gonna need to do a clean install.

Recovery will install Mojave again, unless you cheat and create a Recovery partition for El Capitan, but this is an advanced procedure.

 

[sauria]

I did not know that Mojave supported nVidia graphics?

 

[tsialex]

I did not know that Mojave supported nVidia graphics?

A lot of Macs from 2012 to 2014 have NVIDIA discrete graphics, from the Kepler generation. Apple still supports NVIDIA Kepler GPUs with Big Sur.

 

[K2000]

You can downgrade if your have a TimeMachine, than you can go back to that image, but not successively. If you don't have a clone from your El Capitan install, you will gonna need to do a clean install.

Does this mean Time Machine will install El Capitan in one step, if I pick the El Capitan file versions I backed up? Because that would be so easy...

 

[sauria]

A lot of Macs from 2012 to 2014 have NVIDIA discrete graphics, from the Kepler generation. Apple still supports NVIDIA Kepler GPUs with Big Sur.

Thank you!

 

[tsialex]

Does this mean Time Machine will install El Capitan, if I pick the El Capitan file versions I backed up? Because that would be so easy...

Nope, won't work. El Capitan don't even understand your disk right now. Mojave converted it to APFS.

You need to clean install El Capitan, nuking your disk first, then restore a TimeMachine backup.

 

[K2000]

Nope, won't work. El Capitan don't even understand your disk right now. Mojave converted it to APFS.

You need to clean install El Capitan, nuking your disk first, then restore a TimeMachine backup.

Do I use Apple's El Capitan installer program to wipe the disk? Or do I need to use Disk Utility in Recovery Mode...?

Sorry, I'm a total noob

 

[tsialex]

Do I use Apple's El Capitan installer program to wipe the disk? Or do I need to use Disk Utility in Recovery Mode...?

Sorry, I'm a total noob

You need to nuke your Mojave install booting from another drive. Recovery can't nuke itself. Make a createinstallmedia El Capitan USB installer - yes you'll need to get one.

 

[K2000]

You need to nuke your Mojave install booting from another drive. Recovery can't nuke itself. Make a createinstallmedia El Capitan USB installer - yes you'll need to get one.

Something’s going wrong. It seemed like I installed the ElCapitan installer on my external disc (it’s a portable USB disc drive, not thumb drive). The name of the disc changed to “El Capitan installer” and (etc). But when I restarted with Option pressed down, I never saw a list of bootable drives. The screen stayed dark, for about 5 minutes (with Option depressed). Nothing came up. I checked Startup Security Utility and the message was Firmware Password Protection is Off (I disabled SIP). Is it possible that i’m using the wrong script? I used this command:

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/YOURDRIVE --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

(I used the name of the drive - not generic YOURDRIVE)

Found here:

Create a bootable installer for macOS - Apple Support

You can use a USB flash drive or other secondary volume as a startup disk from which to install the Mac operating system.

support.apple.com

 

[K2000]

(Deleted for sake of clarity)

 

[K2000]

I’m able to make the USB drive a bootable drive, according to Terminal. However, the next step is where it seems to be wrong: restart holding Option, then a list of bootable drives will appear onscreen (no list appears). The external drive blinks rhythmically like it’s not getting mounted. And even the internal disc does not appear. Maybe the instruction “reboot w/ Option” is wrong, or it could be an issue with my GPU because the monitor is not getting a signal. The screen is black...

Intel processor​

1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
2. Press and hold the Option (Alt) ⌥ key immediately after turning on or restarting your Mac.
3. Release the Option key when you see a dark screen showing your bootable volumes.
4. Select the volume containing the bootable installer. Then click the up arrow or press Return.

From here:

Create a bootable installer for macOS - Apple Support

You can use a USB flash drive or other secondary volume as a startup disk from which to install the Mac operating system.

support.apple.com

 

[K2000]

Ok it’s confirmed that the external drive has a light that’s normallly solid when it’s mounted. When I reboot with Option pressed, the drive doesn’t mount (lights keep blinking) and I don’t get a choice of drives to boot from (startup manager doesn’t launch)

 

[K2000]

My USB drive is a WD “My Passport” drive with a spinning disc, on loan. I should probably go get a thumb drive.

 

[minifridge1138]

Which USB port did you attach the external drive to?

 

[tsialex]

My USB drive is a WD “My Passport” drive with a spinning disc, on loan. I should probably go get a thumb drive.

Won't work, a lot of WD drives (really the USB->SATA adapter from WD) have a firmware that creates a secondary drive to install some management/drivers/backup software - these drives are usually not bootable with a Mac. Get an USB key.

 

[K2000]

Thanks for the info!

If it matters, my boot drive is an SSD in a PCIE slot (on a OWC Accelsior) not SATA.

I was using the USB port on the front of my Mac, for the WD drive.

 

[K2000]

Deleted for clarity

 

[K2000]

Using a San Disk thumb drive now.

 

[K2000]

I put the original graphics card in and it seems to be working. I have a display screen in Startup Manager. I thought the GeForce GTX 680 would always show the startup screen, but apparently not for this operation. But the PCIE mounted drive doesn’t show up in the list of drive options. Do I have to mount the PCIE drive in a SATA slot, in order to have it recognized?

 

[K2000]

There was problem wiping the PCIE drive, so I'm taking it into the shop for help. Thanks.