Imac 27" 2011 Non Starter

[Mr Robert]

I started having problems when my Mac would start, seeming the hard drive had eventually corrupted and couldn't get past the start up bar

I have purchased a new drive Sandisk SATA iii 512mb + Heat adapter (OWC) but after checking realised this may not be compatible as the iMac only has SATA II (correct me if i am wrong!), I had cloned the drive with Carbon Copy Cloner from my Macbook pro drive 13" 2011 and even tried booting from a USB OSX High Sierra (Same Issue)

So I regrettably reformatted the original 1tb OEM Drive (lost all prior data) and it mounts and works fine in a caddy on my Macbook, reinstalled as the original drive into the mac and it basically slowly starts the Apple load up process and then goes pale grey and restarts continuously (same issue as before).

Please help!

Does this sound like a graphics card issue?

 

[Ausdauersportler]

Probably your first analysis was not correct: In most cases this symptom is more likely a sign of a dying video card. I saw this happen a dozen times.

If the video card is still working you should be able to use the internet recovery of your iMac to install the last supported MacOS directly over network from apple servers (search which buttons to press at start) onto your internal disk. There is no need to use another Mac to install a system on the iMac.

After download and during install you will see the video card coming up (or not) and then you may decide what to do. If my guess is good then just hop over to this thread and get an idea what replacement cards are available.

 

[Mr Robert]

Can I

Probably your first analysis was not correct: In most cases this symptom is more likely a sign of a dying video card. I saw this happen a dozen times.

If the video card is still working you should be able to use the internet recovery of your iMac to install the last supported MacOS directly over network from apple servers (search which buttons to press at start) onto your internal disk. There is no need to use another Mac to install a system on the iMac.

After download and during install you will see the video card coming up (or not) and then you may decide what to do. If my guess is good then just hop over to this thread and get an idea what replacement cards are available.

Can I ask is the SATA III SSD Compatible?

 

[Ausdauersportler]

Your iMac 2011 has two SATA III ports - the disk would also fall back to the slower SATA II speed, if the chipset would not support this. At the SATA 0 port the internal HDD was connected, the SATA 1 port has been used for BTO systems delivered with stellar modern and expensive Apple SSD drives in 2011

Now we can use this port with a second iMac SATA/PWR cable to connect a second disk...

 

[Oadbylad]

Ive the same model iMac as the OP but borought it as spares/repair it came without an HDD i had a SDD
Question is which port do i use?

 

[Ausdauersportler]

SATA 0 (boot disk) - SATA III
SATA 1 (spare or boot disk, does not make a difference) - SATA III
SATA 2 (ODD aka DVD) - SATA II, only

The system walks through the internal SATA ports on the search for a bootable device if no explicit choice has made before (and stored to the NVRAM) and boots in this case from the SATA 0 ports disk taking the first bootable partition.

When you picked in the systems pref pane another disk or partition this one is the first to boot from.

 

[Oadbylad]

Thank you
Ausdauersportler ?

 

[Juicy Box]

reinstalled as the original drive into the mac and it basically slowly starts the Apple load up process and then goes pale grey and restarts continuously (same issue as before).

I had this same exact issue with a dumpster pulled Mid 2011 iMac. It appeared to the just a corrupt HDD at first which was an easy fix. But, it also had a fried GPU.

I did an oven bake of the GPU and it works great now, going on over a year now.

Can I ask is the SATA III SSD Compatible?

SATA is backwards compatible, so you can have a SATA III drive work with a SATA I port or have a SATA I drive work with a SATA III port. It will be as fast as what ever the slower standard is.

As @Ausdauersportler posted, your iMac has two SATA III and one SATA II. If you are just swapping out the HDD for an SSD, that cable would be connected to one of the SATA III ports.

Ive the same model iMac as the OP but borought it as spares/repair it came without an HDD i had a SDD
Question is which port do i use?

You can use any of them to boot from, it would be faster to use SATA0 or SATA1.

You could also use both in a SW RAID0 set up. This would give you around 900-1000MBps read speeds if using SSDs.