2009 C2D 27" iMac won't accept RAM upgrade, 3 beeps

[Buffsteria]

We have a 2009 27" Core 2 Duo iMac. It came with 4GB RAM. We upgraded this, first to 8GB and now we were trying to get it to 16GB.

WE HAVE 100% COMPATIBLE RAM FROM CRUCIAL.

THE RAM IS GOOD.

THE RAM IS NOT FAULTY.

YES THIS MODEL CAN TAKE 16GB OF RAM

The iMac boots up with one slot full, or two slots full.

THE iMAC DOES BOOT UP WITH ONE SLOT FULL. I HAVE DONE THIS.

However, no combination will boot up if all 4 slots are filled. I can fill up the two top slots with any combination of RAM modules and the iMac boots.

When I populate the two bottom slots it doesn't boot up. And so I thought the slots were the problem. BUT....

If I populate JUST the two bottom slots the iMac boots up!

I don't know what's going on. The only time I got it to boot with 4 slots was when I replaced one of the Crucial modules with a Samsung module I extracted from an older Mac. But that module was PC8500. The entire iMac RAM ran at 1067 instead off 1333 because of this. Other than that, every single combination that fills up all four slots cause 3 beeps to sound off.



Specs: 2009 27" Intel Core 2 Duo iMac 3.06Ghz
RAM: Crucial, 4x4GB
Configuration: 512Meg x 64
DDR Timings: CL=9
DIMM Type: Unbuffered
Density: 8GB Kit (4GBx2)
Error Checking: NON-ECC
Megabytes: 8192
Memory Type: DDR3 PC3-10600
Package: 204-pin SODIMM
Replenishment Flag: Y
Speed: DDR3-1333
Voltage: 1.5V

http://www.amazon.com/Crucial-204-pin-SODIMM-PC3-10600-CT2CP51264BC1339/dp/B003DZJQQI/

 

[GGJstudios]

My first guess is that the RAM isn't properly seated. Some RAM modules take quite a bit of pressure to fully seat them.

 

[Buffsteria]

My first guess is that the RAM isn't properly seated. Some RAM modules take quite a bit of pressure to fully seat them.

I find it puzzling that that one slot accepts only one of the sticks. Unfortunately I can use it. I press real hard. I guess I can try even more pressure but I'll be afraid of wrecking everything.

 

[Macman45]

I find it puzzling that that one slot accepts only one of the sticks. Unfortunately I can use it. I press real hard. I guess I can try even more pressure but I'll be afraid of wrecking everything.

Don't be...It takes a lot of OOMPH to install the sticks...I had the same thing when I upgraded my iMac to 16GB..I really had to press hard to get them in...You should get a loud click when they are properly seated. If they are sitting proud of the other sticks then you don't have them all the way in...Kernel panics are a sure sighn that at least one of the modules is not correctly pressed home. Be brave.

 

[Dadioh]

Sounds like it is because you are trying to use 1333MHz RAM in a machine that is designed for 1066MHz? I guess with just 2 slot it manages to scrape by with marginal timing but with 4 slots filled the timing is not right. As soon as you insert a single stick of 1066 (PC3-8500) then it forces all the slots to run at 1066 and you are fine. I think you need to use 1066 RAM in this case.

I recently upgraded my 2009 iMac to 1333 RAM but mine is the Core i7 where the memory controller is built into the CPU. In your case the Core 2 Duo relies on a Northbridge chip for memory controller.

 

[GGJstudios]

I find it puzzling that that one slot accepts only one of the sticks. Unfortunately I can use it. I press real hard. I guess I can try even more pressure but I'll be afraid of wrecking everything.

If you're certain all RAM is seated, it's possible you have one or more defective modules.

 

[Buffsteria]

Sounds like it is because you are trying to use 1333MHz RAM in a machine that is designed for 1066MHz? I guess with just 2 slot it manages to scrape by with marginal timing but with 4 slots filled the timing is not right. As soon as you insert a single stick of 1066 (PC3-8500) then it forces all the slots to run at 1066 and you are fine. I think you need to use 1066 RAM in this case.

I recently upgraded my 2009 iMac to 1333 RAM but mine is the Core i7 where the memory controller is built into the CPU. In your case the Core 2 Duo relies on a Northbridge chip for memory controller.

I'm no expert but this does seem to make sense! I'll look into it, thanks!

 

[Buffsteria]

Sounds like it is because you are trying to use 1333MHz RAM in a machine that is designed for 1066MHz? I guess with just 2 slot it manages to scrape by with marginal timing but with 4 slots filled the timing is not right. As soon as you insert a single stick of 1066 (PC3-8500) then it forces all the slots to run at 1066 and you are fine. I think you need to use 1066 RAM in this case.

I recently upgraded my 2009 iMac to 1333 RAM but mine is the Core i7 where the memory controller is built into the CPU. In your case the Core 2 Duo relies on a Northbridge chip for memory controller.

Just wanted to comment again and say this was the right answer. Thank you! I've changed the RAM to 1066Mhz and now it has a full 16GB.