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A2115/2019/ Procesador desde 3.0 GHz de 6 núcleos core i5, hasta 3.6 GHz de 8 núcleos i9. Lanzado el 19 de marzo 2019.

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iMac doesn't boot with four identical RAM plates

I have an iMac 5K 2019 where I’ve replaced the stock RAM with two plates 8GB (2666MHz) each (HyperX HX426S15IB2K2/16).

Today I bought two more identical modules and tried to install them. So now I have 4 identical modules. But my iMac didn’t start. I can only feel that warm air is coming from the iMac, but nothing more: the screen is black.

I’ve tried next configurations:

  • It boots with any single module installed in any slot;
  • It boots with any two modules installed in slots 1+3 or 2+4;
  • But it doesn’t boot with any two modules installed in 1+2 or 3+4 slots;
  • It also doesn’t boot with any thee modules installed in any thee slots

So I think, that modules are ok, and the slots are also ok. So what could be the problem?

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Are you able to get to the onboard diagnostics when you restart the system pressing the D key?

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I've tried but got no reaction. Black screen and nothing more.

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I’m having the same identical issue 4 x 8 GB HyperX modules each pair works in either bay pair and switching the module bay order. It just does not work with all 4 installed, called Apple and all they could advise is take it to the Apple Store for a check up

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@paul_carroll - Sounds like you got the wrong RAM or they are defective. Try a another source.

Make sure you have the correct SO-DIMMs! 4 - 260-pin PC4-21300 (2666 MHz) DDR4

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I check on this website for compatibility. https://www.mrmemory.co.uk/memory-ram-up... And it says it compatible. So unless they have it wrong then pretty sure it should work.

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Give this a shot. Install all the RAM. Now we are going to zap the PRAM. Hit the power button and immediately hold down the par,option and command keys and hold them down. The machine should reboot. Continue holding down until it tones three times and release the keys and allow it to boot.

UPDATE 4/19/20

RAM Type:PC4-21300 DDR4Min. RAM Speed:2666 MHz

Details:Supports 2666 MHz PC4-21300 DDR4 SDRAM SO-DIMMs (260-pin).

Standard RAM:8 GBMaximum RAM:128 GB*

Details:*By default, 8 GB of RAM is installed as two 4 GB memory modules (and two slots are unoccupied). For some curious reason, Apple only permits this model to be configured at the time of purchase with 16 GB or 32 GB of RAM for an extra US$200 or US$600, respectively. However, as first determined by OWC, it actually can support up to 128 GB of RAM with four 32 GB memory modules.

At this point I would replace the original RAM and then attempt adding your new RAM. Also your new RAM may just not be compatible with this MAC. I would also contact Kingston and ask if the HyperX HX426S15IB2K2 is rated for this iMac.

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Do you mean holding Command + Option + P + R?

I've tried it but got no reaction. Like if nothing happened. I only feel warm air blowing from the back of iMac, but nothing more. I've tried to press the keys before switching the mac and immediately after. I've waited for a minute holding the keys, but nothing had happened. No reboots, no apple logo, no beeps...

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Let's make sure you are doing it correctly. here's a video on doing it:

https://www.youtube.com/watch?v=N5laIcLM...

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Yes, I did it as in the video. Tried with a stock magic keyboard and with my USB keyboard.

And I also did SMC reset (actually, it's difficult not to do it when you install new RAM: if I understood correctly, the only thing II have to do is to unplug the power cord for 20 seconds, and I have to do this to open the RAM cover)

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It does take a bit of time to boot when the system needs to validate the new RAM config.

Put the RAM back in make sure the RAM is fully seated. Restart the system, let it sit for a half hour the system should have booted by then.

If not take the original RAM out and put the new RAM in its place (slot for slot) did the system start up then?

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I tried to leave it turned on with the black screen and new modules inside for an hour but it gave no result.

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About the original RAM: I don't have it now. I only have 4 identical, non-original 8Gb modules.

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Time to get another set from a known iMac RAM supplier ;-{

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I had the similar experience today. I bought upgrades for two 16 gb rams, definitely different brand from what's original to my iMac, and it wouldn't start. So what I had installed were 4 gb original rams on slots 1 and 3, and added the 16s to slots 2 and 4, and pc would not boot. I could hear the machine work but nothing loads on the screen. I heard this could happen if your rams are not identical. What I did after is I took off all rams and added the 16s I got to slots 1 and 3, and viola! It worked perfectly. I think it's probably the ram channels wanting the same ram profile.

As for your case, I am sorry it's not working with all 4 identical rams. Maybe try using just slots 1 and 3 with identical rams? Also make sure they are placed correctly and push them all the way in.

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Have the same problem for the past two days.

Having four identical apple OEM rams but the system won't turn on with all four slots installed. It will with 3, with 2 but not with 4. Also, it doesn't matter which order you put or which ram of the four one you installed. All of them are working in pair of 3s or 2s but not all together.

I am really bamboozled.

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each ram is 4GB Micron OEM

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I keep working with 12GB on, but this additional 4 GB will be very helpful

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I too am unable to start imac27 2020 with 128 go (4 x own 32gb). It does start and seems to work ok with original 2 Apple 4 go ram in slots 1 and 3 and with 32 gb owc ram in slots 2 and 4.

There was no start activity at all with 4x32gb installed (double checked properly and full in place)

is it possible that it has to initialize with Apple ram installed then change out last two Apple ram with remaining own ram?

Any other ideas as to how to get full 128 go ram working?

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I have not been able to resolve this. At this point I am pretty convinced that there is something wrong when all 4 slots occupied (maybe firmware). I have tried with 3rd party ram and it is the same: the iMac will boot up with any combination (3rd party or OEM in any slot) but not when all 4 slots are occupied.

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@Greg Pap - Did you try taking the system into Apple to see if they know. Did you try running the newer macOS to see if that altered things.

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