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Changed RAM in Retina iMac27, doesn't turn back on

M

MR_Boogy

macrumors regular
Original poster
Apr 6, 2012
145
19
I put some additional RAM in my new iMac but now it doesn't run on. No lights, no chime, nothing. I've seen it can take time doing a start-up RAM check but we're talking several minutes here.

I removed the new RAM and put the old back in the original slots, and got it to restart. But put the new ones in, no beeping or anything after several minutes.

Do I just assume these DIMMs are shot? They are ones Crucial sell specifically for this model.
 
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They’re not reading the new RAM at all, so I would guess so. What RAM is in there now vs what ram did you buy?
 
Have you tried mixing DIMMs? Run with one of the new RAM sticks in one slot and Apple-supplied in another. You might be able to figure out if one or both are problematic for your system.
 
poked said:
They’re not reading the new RAM at all, so I would guess so. What RAM is in there now vs what ram did you buy?
Click to expand...
It came with 2x4Gb in slots 1&3. I bought 2x16Gb Crucial. I tried both putting them in 2&4 with the Apple ones still in (I know there can be a speed penalty but it should work) and putting them in 1 & 3 instead.

Ledgem said:
Have you tried mixing DIMMs? Run with one of the new RAM sticks in one slot and Apple-supplied in another. You might be able to figure out if one or both are problematic for your system.
Click to expand...
Is that supported, if they are different sizes?

The issue is I don't know if the Mac should chime then do a memory test, or after. I do not know how long testing 32GB of RAM should take but I am guessing a minute or so tops? I did notice the new ones seemed quite warm when I pulled them which made me think they were possibly doing something, but 5-10min is definitely not right, right?

It's from Amazon so it's not a huge issue just a PITA as I want it usable (I run VMs so 8GB is really limited).
 
Is this a 2020 iMac 5K?

I recall plenty of threads about issues mixing Apple and non-Apple RAM in those models. The consensus as I recall was to remove the Apple RAM and use only non-OEM RAM in the total capacity you want.
 
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Yes but I tried the new RAM on its own too.
I think I'll just return it, figure bad luck.
 
Very unusual for Crucial RAM to be bad.
Try putting a single stick of Crucial in Slot 2 (with all other slots empty). (Slots counted from top).
Then try the other Crucial stick in Slot 2 (with all other slots empty).
This is just to determine which stick is bad.
You will have black screen for ~30 seconds. You can very faintly hear fan from back vent.
RAM is quite difficult to seat properly (but do not force it).
Do you have a screenshot or pic of your RAM, so we can verify is right spec?
What model of iMac do you have?
 
@wilberforce what do I expect to see with a single DIMM, surely this will fail as they have to be in pairs?

I had wondered if they were seated right, but I have no problems getting the original ones back in. The plastic is slightly thicker on the new ones. I bought: https://www.amazon.co.uk/gp/product/B07TKZKPJV/ - if anyone can confirm these are good/bad it could help!
 
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d000hg said:
@wilberforce what do I expect to see with a single DIMM, surely this will fail as they have to be in pairs?

I had wondered if they were seated right, but I have no problems getting the original ones back in. The plastic is slightly thicker on the new ones. I bought: https://www.amazon.co.uk/gp/product/B07TKZKPJV/ - if anyone can confirm these are good/bad it could help!
Click to expand...
Those are the exact same DIMMs that I purchased for my 2020 iMac.
@CWallace is correct: you can put in a single DIMM (or any combo of DIMMs), it is just that the performance will not be optimal.
 
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TLDR; faulty RAM

I ordered another 2x16GB (identical) last night and it came today. I removed the stock RAM and put the 2 replacement DIMMs in their place - started up and reported 32GB @ 2667 MHZ. Added the stock RAM back and it showed 40Gb @ 2133MHz (worth a try right).
Took it all out and put the original Crucial 2X16 in... restarted, waited 2minutes, just sat there. Pulled the power, swapped them for the replacement, restarted, 32GB @ 2667MHz.
If I'd bought them as 2 individual DIMMs I'd have figured out which was faulty but they came as a pair so I'll just return them.

Is there a market for 4GB Apple RAM DIMMs? I have 2, as well as an unopened magic mouse and keyboard combo I don't want. Are they worth listing on eBay/Facebook?
 
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d000hg said:
TLDR; faulty RAM

I ordered another 2x16GB (identical) last night and it came today. I removed the stock RAM and put the 2 replacement DIMMs in their place - started up and reported 32GB @ 2667 MHZ. Added the stock RAM back and it showed 40Gb @ 2133MHz (worth a try right).
Took it all out and put the original Crucial 2X16 in... restarted, waited 2minutes, just sat there. Pulled the power, swapped them for the replacement, restarted, 32GB @ 2667MHz.
If I'd bought them as 2 individual DIMMs I'd have figured out which was faulty but they came as a pair so I'll just return them.

Is there a market for 4GB Apple RAM DIMMs? I have 2, as well as an unopened magic mouse and keyboard combo I don't want. Are they worth listing on eBay/Facebook?
Click to expand...
Good to hear.
The Apple RAM is probably worth about $20 (or £20). I decided to just keep it as backup or maybe for when/if I sell the iMac.
Unopened mouse and keyboard should be worth selling. Might best to sell separately.
 
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wilberforce said:
On the other hand, if you plan to sell or trade-in the iMac in the future, might be best to keep the mouse and keyboard with it.
Click to expand...
Maybe but I plan to use it until it dies, most likely. My 2012 Mac Mini was still actually quite adequate in performance it just had too many things breaking. Specs say my bottom-spec iMac is 2X as performant so as long as it runs a recent MacOS reliably, I see myself keeping it. By then, Apple will probably have dropped support for keyboards and mice :)
 
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