Reddit reviews Crucial 8GB Single DDR3/DDR3L 1866 MT/s (PC3-14900) 204-Pin SODIMM RAM Upgrade for iMac (Retina 5K, 27-inch, Late 2015) - CT8G3S186DM
We found 4 Reddit comments about Crucial 8GB Single DDR3/DDR3L 1866 MT/s (PC3-14900) 204-Pin SODIMM RAM Upgrade for iMac (Retina 5K, 27-inch, Late 2015) - CT8G3S186DM. Here are the top ones, ranked by their Reddit score.
Increases system performanceCompatible with Apple iMac (Retina 5K, 27-inch, Late 2015) iMac17, 1 onlyAll memory stick modules extensively tested at the component and function levelMeets or exceeds, Apple's quality standards and requirementsEasy installation
I can confirm that a pair of [Crucial CT8G3S186DM 8GB] (https://smile.amazon.com/gp/product/B01979WD4U) also works.
i used these, which many other people have used too:
https://www.amazon.com/gp/product/B01979WD4U/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
they are also crucial sticks, just 1866 instead of 1600. i went from 8gb (ds1019+, same cpu as 918+), to 12gb and then a few weeks later 16gb. perfect and flawless for about 6 weeks now.
if you read through the reviews for that stick, you will see many mention synology.
EDIT: my apologies, i see that these are the same ones you originally linked too. at any rate, these have been perfect for me.
Pull the RAM, and put in the stock RAM, if the problem goes away, the problem is most likely the RAM you purchased. Some systems are really particular about things. This is what I have in my 918+.
this is a good guide. I bought the 8Gb Crucial Sticks (2x) found here, which are the "newer version" listed on the 8gb link of the blog post: https://www.amazon.com/Crucial-PC3-14900-204-Pin-Upgrade-27-inch/dp/B01979WD4U/ref=dp_ob_title_ce?th=1
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They are working fine and I did a memory test using the Synology Assistant program after I installed them. Be warned the memory test on 16gb of ram takes approximately about 6+ hours to perform after a reboot.