Chosen Solution
This is not my first run in with this. The first time it happened I assumed something had borked on my logic board, as I had been tinkering around with it a lot (replaced the GPU and CPU). I figured I had been indelicate somehow. So, I purchased a new logic board on eBay. I slapped it all back together and used a temporary hard drive, as I knew I’d need to upgrade the firmware to recognize my existing partitions (I was running Mojave, so they’re APFS). I started off installing Mountain Lion, and it recognized the RAM in both slots. After installing High Sierra, the left side no longer recognizes DIMMs in either position. My theory is that this is something to do with the firmware update required to install High Sierra. Has anyone else seen this? None of the networking devices, WiFi nor Ethernet, have worked in any install or firmware version with this logic board, but I suspect that’s an entirely separate issue. Update (06/28/2020) Just to clarify, in both scenarios it would recognize 16GB of RAM, but only if both 8GB DIMMs were in the two right slots. As for the DIMMs, they are 8GB each. Here’s a shot with relevant info:
https://imgur.com/a/XJ3AiCs The networking issues are indeed on the replacement board. The seller has a good return policy, however. This entire ordeal makes me think there’s nothing wrong with my original logic board. Or wasn’t, until I accidentally broke the power button connector off the logic board. @danj
Keep in mind the newer system firmware in Sierra is able to support the newer 8 GB SO-DIMM’s. I know a few folks who have loaded up their systems to 32 GB. For reference:
While this is using smaller sized SO-DIMM’s it expresses the correct loading in the system.
