2019 27" iMac shows black screen with 4x16GB RAM

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2019 27" iMac shows black screen with 4x16GB RAM

Hi.

I recently upgraded my 2019 27" iMac from 16GB (4x4gb) to 64GB (4x16GB). the problem now is the Mac starts but only with a black screen. When I reinstall the original memory it starts fine. When I install 2x4GB with 2x16GB it works fine. The black screen only appears when I install all 4x16GB modules. All of the 16GB modules work fine as I have tested them all individually.

At the moment I have 40GB installed. Volume A 4+16 Volume B 4+16. Mac works fine. It even works fine with 3X16GB installed but will not work with all 4x16GB installed.

Any suggestions.

macOS Sequoia 15.7.2

iMac 27″, macOS 15.7

Posted on Dec 13, 2025 4:26 AM

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Answer 1

Top-ranking reply

Old Toad

Level 10

215,316 points

Dec 13, 2025 10:08 AM in response to den.thed

den.thed wrote:

What brand and where did you purchase those 16GB RAM modules...?

iMac's are very RAM picky and that is a common problem when replacing all 4 modules.

If it startup & runs on 40GB or 52GB of RAM with no errors or crashing, then it might be best to do that.

OWC macsales.com is about the only RAM supplier that could actually pull together a working 4 module kit.

see > https://eshop.macsales.com/shop/memory/imac-2019-27-inch

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Answer 2

den.thed

Level 10

90,916 points

Dec 13, 2025 7:12 AM in response to Vincentow

What brand and where did you purchase those 16GB RAM modules...?

iMac's are very RAM picky and that is a common problem when replacing all 4 modules.

If it startup & runs on 40GB or 52GB of RAM with no errors or crashing, then it might be best to do that.

OWC macsales.com is about the only RAM supplier that could actually pull together a working 4 module kit.

see > https://eshop.macsales.com/shop/memory/imac-2019-27-inch

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Answer 3

John Galt

Level 10

155,234 points

Dec 14, 2025 10:52 AM in response to Vincentow

I bought them from Mr Memory whom I have dealt with for a number of years and never had a problem.

Until now. Macs are intolerant of memory that does not meet its published specifications. Return what you bought and purchase RAM from a vendor known to support Macs. OWC / MacSales is the only vendor that I have used and can personally recommend.

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