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I bought a pair of Crucial 8GB DDR3 1866MHz SODIMM for my iMac 27 5K Retina Late 2015. I suspect the SODIMM that I received is 1600MHz, potentially counterfeit.

Here is my question

  1. Is there any way to read the SPD data for the speed, CL settings, and manufacturer ID?

  2. How do I find the actual speed. Is the System Report -> Memory the actual speed or reading from SPD? I need both information.

  3. How do I check if it's a genuine Crucial memory? (EDIT: I called Crucial. They said the material number 310536 isn't matching. They are investigating)

The Crucial part number is CT102464BF186D.C16FN.

CT102464BF186D

The marking on Micron DRAM chip is D9QBJ.

D9QBJ

According to Micron the part number is MT41K512M8RH-125:E. Here is the link for datasheet. -125 means 1.25nsec speed grade. 1/1.25nsec = 800MHz which is 1600MHz since DDR is "double data rate".

FYI: Crucial web said CT102464BF186D is not compatible with Mac, but many people reported success and stable with their late 2015 iMac while small number of people reported random shutdown. It's my wild guess they hit the counterfeit DIMM that has the SPD programmed for 1866MHz when the DRAM chips are 1600MHz rating.

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    Have you looked in the System Information app? (Apple menu > About This Mac > System report > Memory) It lists the specs of all installed memory. – Steve Chambers Sep 13 at 16:14
  • Did you talk to the dealer who sold you this? Is it a reputable dealer? – jmh Sep 13 at 18:45
  • Unfortunately my iMac died when I shutdown last night for the memory installation. Now I have to get a new PSU as well. It's a Chinese online shop. So far the seller hasn't agreed with the return & refund. I need to give him a definite evidence. – Kenji Noguchi Sep 14 at 5:36
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The RAM does appear to be counterfeit as far as I can see.

I have that type of genuine Crucial memory (CT102464BF186D.C16FN) here - but it doesn't look like your picture.

The PCB is almost identical, but some markings on it are off. The number of components mounted at the top of the board are very much different. The actual DRAM IC on my memory has FPGA code C9BCM, which according to Micron is a 1.07 nsec rating - equalling a 1866 Mhz speed.

To top it off, the label looks very much the same - but instead of "Product of China", mine says "Assembled in USA".

I can't say for sure that this means that it is counterfeit - it could be some kind of labelling/production error, or another revision of the same product or similar.

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  • That's a great info. Thanks! I'm more inclined to say it is counterfeit. It's beyond of revisions if Crucial made DIMMs with different speed rating chips for the same part number. I called Crucial and sent the pictures. They will investigate. – Kenji Noguchi Sep 14 at 5:48

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