When I purchased my iMac (Retina 5K, 27-inch, Late 2015) I had 16GB of RAM installed. I bought 16GB more today to max out my RAM at 32GB, and when I installed the new sticks (2x8GB sticks =16gb) my computer wouldn't boot up. It turned on, but it was just a black screen. I took out one of the new sticks (3 remaining in the computer) and it turned on just fine. Is there a reason this is happening, or a way to fix it?
iMac with Retina 5K display
I had this problem too. I contacted the seller (on Amazon) of my 3rd party RAM (Adamanta) and they told me to do this:
Counting slots from the bottom up, OEM sticks should be in slots 1 and 3, and you should have your machine unplugged while swapping out RAM.
Take OEM RAM out of 1 and 3.
Put 3rd party RAM in 1 and 3.
Plug in and power on. After ~30s your machine should boot to the OS. After it does, confirm that your new ram is recognized, then turn off computer.
Put OEM RAM in 2 and 4.
Plug in and power on. Should recognize all 4 RAM sticks.
I have no idea why this order mattered and makes no sense to me, but I hope it works for you!
I had this problem too. I contacted the seller (on Amazon) of my 3rd party RAM (Adamanta) and they told me to do this:
Counting slots from the bottom up, OEM sticks should be in slots 1 and 3, and you should have your machine unplugged while swapping out RAM.
Take OEM RAM out of 1 and 3.
Put 3rd party RAM in 1 and 3.
Plug in and power on. After ~30s your machine should boot to the OS. After it does, confirm that your new ram is recognized, then turn off computer.
Put OEM RAM in 2 and 4.
Plug in and power on. Should recognize all 4 RAM sticks.
I have no idea why this order mattered and makes no sense to me, but I hope it works for you!
I tried this and it did not work. Now for the strange part. I recently purchased 216 GB models the speed turned out to be slower than the 2400 on my new iMac so the plan was to return them. I ordered a new set to 16 GB models 2400 and when I put them in by themselves they work just fine, when I put in the stock OEM ram it worked just fine, when I put in the stock OEM ram and the new adamant a ram I got a black screen and it never turned on regardless of order. Now, when I put in the slower 32 GB of RAM with the new ram it worked just fine. The OEM ram and
I purchased this RAM - https://www.amazon.com/gp/product/B01LZ538E2/ref=oh_aui_detailpage_o01_s00?ie=UT F8&psc=1
I installed it into the empty slots, it didn't work. I took one out, and it worked. Should I try and move the existing RAM around?
I'd return the RAM and get it from OWC (macsales) or Crucial; I'm not at all familiar with this - what is puzzling me is that Apple used to use Hynix as factory installed RAM, but I do not know if that was the brand or if it has anything to do with the brand you bought.
That might be either a bad module or a problem with the slot. What brand RAM did you buy? And, did you install the new modules in the two empty slots or did you move the existing RAM around?
Bargain basement third party ram is prone to faults like that. Buy better ram https://eshop.macsales.com/shop/memory/iMac/Retina-5K2015/DDR3L
Black Screen after RAM upgrade
