Late iMac 27" only seeing two memory sticks

Still trying to figure this out. I have a very nice 27" late 2009 iMac. The hard drive started having issues and tests indicated it was getting ready to die (as well as real time symptoms). So I purchased a new 512GB Crucial SSD, I opened the iMac, replaced the ssd including a new temp sensor cable, blew out dust, closed it back up. Worked fantastic (I preloaded El Capitan on the SSD).

BUT it was now only reading 8 of the 16 GB ram. So I removed all the Ram again, blew out any dust, and reset the ram, still no joy, So I reset the NVRAM. Zapped PRAM, and reset SMC, no joy.

I tried the following:

Only two sticks on left side slots, 8GB

Other two on left side. 8GB

All four 8GB

One from each group two sticks. 8GB

Now two on only right side 8GB

Now other two on right side 8GB

Same sets of two, but one on lower left and one lower right, 8gb

same two on upper left and upper right 8gb

Now the same procedure with the other two sticks.

No matter how many, or what order, or combination I place them only two of the sticks are recognized.

So this is telling me that the slots themselves are functioning

SO I check the memory, They are 1033 and have been working since the Apple store placed them in the iMac six years ago when they replaced the Hard Drive (Recall service).

This memory was for the Early 2009 iMac if my reading forums, and sites correctly.

So I ordered NEW Crucial 1066 4gb DDR3 PC 8500 sticks.

In the meantime I wipe drive reinstall El Capitan.

They come I install them do the Zap PPAM, NVMC and SMC resets. still 8GB

I do the same trial and error tests with the same results listed above same results.

I verify the new memory is good on another computer.

The computer runs great, just with 8GB ram.

iMac (27-inch, Late 2009), 2.8 GHz Intel Core i7

ATI Radeon HD 4850 512 MB

8 GB 1067 MHz DDR3

Model: 525.11 GB Crucial_CT525MX300SSD1

El Capitan (10.11.6 (15G22010)

Ideas, suggestions would be appreciated.

I posted this previously but chemo meds do a wonder to focus and memory, my apologies.

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First Replacement based on what was already in the iMac, based on assumption two sticks not working

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Crucials I bought after double, triple, quadruple checking Apple, and other sites.

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Avant, what has been in and running in the iMac since 2014?

Beantwoord deze vraag Dit probleem heb ik ook

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RAM Type: PC3-8500 DDR3 Min. RAM Speed: 1066 MHz

Details: Supports 1066 MHz PC3-8500 DDR3 SO-DIMMs (204-pin).

Standard RAM: 4 GB Maximum RAM: 32 GB*

Details: By default, 4 GB of RAM was installed as two 2 GB SO-DIMM modules. Two slots free.

*Officially, this model supports a maximum of 16 GB of RAM. However, as carefully confirmed by Other World Computing, this model can support up to 32 GB of RAM if it is running Mac OS X 10.6.3 "Snow Leopard" or higher in 64-bit mode and has been updated to use the latest EFI version. It is limited to 16 GB of RAM in 32-bit mode.


Before i bought the new ram. I double, triple, quadruple checked Apple, EveryMac, OWC, Crucial, iFixit, Xlr8 your Mac and assorted forums to make sure the "wrong" memory was installed though previously working fine) and I was indeed purchasing the correct Ram.

Thank You


Check power connection maybe try fan controller ssd in that imac can throttle the fans


Hi Mark S., sorry I am not sure I understand your suggestion is.

It is a Crucial 500-ish GB SSD, it has a temperature control cable (OWC) attached.

Are you saying that if the cable is not attached properly, the iMac is not sensing it, thus adjusting the fans, and possibly the power to the logic board (and RAM)?

I know I did not mention the temp Sensing cable so I apologize if I am butchering what you said.

Thank you,



Well I have have run out of ideas with this.

Either I touched something on the motherboard causing only two of the memory slots to work.

There is a hardware/firmware issue not allowing the memory to read more than 2 slots.

Since I cannot replace the hardware to the way it was (dead HDD) and Memory checks out on other systems, assorted memory tests, Grrrr.

So I can run it with the two 4GB sticks for a total of 8GB. But two 8GB sticks so I will have 16GB total.

Or I can replace the logic board.

I appreciate all the responses.

Thank you.


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