Memory Upgrade - slots don't work?

[akorn342]

Hi,
I just got a new 27" iMac, and planned to upgrade the memory to 128 GB. When I opened the memory compartment, the Apple 4 GB modules were in slots 2 and 3. I replaced them with OWC 32 GB modules, and everything is fine when I only have modules in slots 2 and 3. When I have something in slots 1 and 4 (either or both), the computer doesn't boot properly. I tried various modules, including the Apple 4 GBs in those positions, but nothing works. Has anyone else experienced this sort of thing?

 

[robbieduncan]

When you say doesn't boot properly can you describe in more details what is happening? Apple note in the KB

"Note: Your iMac performs a memory initialization procedure when you first turn it on after upgrading memory or rearranging DIMMs. This process can take 30 seconds or more, and the display of your iMac remains dark until it’s finished. Make sure to let the memory initialization complete."

 

[pldelisle]

Hi,
I just got a new 27" iMac, and planned to upgrade the memory to 128 GB. When I opened the memory compartment, the Apple 4 GB modules were in slots 2 and 3. I replaced them with OWC 32 GB modules, and everything is fine when I only have modules in slots 2 and 3. When I have something in slots 1 and 4 (either or both), the computer doesn't boot properly. I tried various modules, including the Apple 4 GBs in those positions, but nothing works. Has anyone else experienced this sort of thing?

Your modules need to be in pairs in channel 1-3 and 2-4.
Try one module at a time in slot 1. You might have a defective module.