Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo processor

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Endless boot loop after RAM install

I'm trying to help my sister-in-law by upgrading RAM and adding an SSD to her late 2009 21.5" iMac. I have successfully managed this in my own machine and created a Fusion Drive.

I installed 4x4gb RAM that match specs of machine and then installed Sierra to the computer. I ran into problems booting the machine after that (never successfully made it into Sierra). Now, the machine boots endlessly, progress bar makes it about 3/4 of the way through then it reboots.

I have (in no particular order):

Put the original 2x2gb RAM back in: no change.

Booted to Recovery mode: reboots before it gets to recovery options.

Booted to Internet Recovery: reboots at Apple logo after getting past spinning globe.

Booted to external drive with a bootable Sierra installer on it (both an external HD and an SD card): crashes and reboots at same spot as before.

Booted in safe mode: get error message and reboot.

Booted to my 27" iMac running Sierra as the Target Disk: kernel panic and reboot (have error message if important)

Looking for any help of where to go from here. All I want is a clean install on the machine with the SSD in place of the optical drive (using the iFixit mount). At this point, I'd even settle for just the SSD if need be, without the Fusion Drive I'd planned. Thanks in advance for any info any of you can help with.

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Who's SSD are you using here?


Can you double or triple check your RAM seating and RAM-speed? I had similar problems recently with a newer iMAC which was rebooting even after I put back everything back to original. The fault in myside was I put a RAM module not perfectly in the slot. Best is put only one RAM (closer to screen) and start there by you can find the error.


Edward C - I suspect I know whats up here and its not the RAM ;-}

But to be sure I need to know what the exact SSD drive being used.


I plan to put in a Crucial SSD, but haven't installed yet. I was doing ram and upgrade to Sierra, then planned on putting in the ssd and creating a Fusion drive. Should I make a bootable Sierra drive on the ssd and then install? I'm concerned because it's not booting to an internal or external right now, so don't know if a new drive will solve the problem. Seems like the issue lies somewhere other than the drive, no?

@moeller22: I'll check the RAM later tonight, putting a single 4gb stick in one slot at a time.


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Lets first talk about the SSD you have decided on using a Crucial MX300 series SSD. Sadly you can't use it in this system as the Crucial MX300 drives are fixed SATA III (6.0 Gb/s). You'll need to get a SATA II (3.0 Gb/s) SSD or one that is able to run at SATA II. As an example lets look at the Samsung 850 EVO SSD spec sheet: Samsung 850 EVO SSD we can see if offers compatibility across all three SATA interfaces SATA I (1.5, SATA II (3.0 Gb/s) & SATA III (6.0 Gb/s). Make sure what ever drive you get states clearly it can run at SATA II. For reference I've posted your systems specs above.

OK lets dig deeper into your current problem:

You maybe hitting an issue with the systems firmware, I would recommend you drop back down to her original RAM and then see if her systems firmware is at the level listed here or newer: About EFI and SMC firmware updates for Intel-based Mac computers. Unless you have the newer firmware boosting a system to 16 GB can create a problem like what you have here.

If your firmware is at the level listed or newer a constant reboot also implies the hard drive is having problems. I would then suspect in the process of upgrading the OS it hit a bad sector and the drive became corrupted.

I would recommend you try to connect your sister-in-law's system to a second Mac system using Target Disk Mode. This will allow you to both backup her stuff as well as try to repair or reformat the drive.

Here's a good writeup on Target Disk Mode, basically once you have the two systems interconnected from your system run Disk Utility to repair her systems drive.

Lastly, keep in mind future OS's may limit what will work on it. So consider the amount of investment you put into the system and what your sister-in-law is using the system for and the apps.

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I really appreciate the insights, Dan. I'll have to look into sending the drive back and getting a backwards compatible drive. I have had good performance out of the Crucial drive and didn't realize there was a compatibility issue. Love learning new things!

I have tried putting her system in Target Disk mode and have not been able to see the drive mount. Is this common? I also tried putting my system in target disk to here and choosing it to boot, it fails at the same point in the boot process. There was some text shown when it tried to boot from my iMacs drive, if that can be helpful, I can type it out (I snapped a picture).

I'll also try reverting to her OEM ram setup tonight and see how it goes.

Thanks again for all the input.


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Aaron Peterson will be eternally grateful.
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