Chosen Solution
When both slots are populated, the system only records 2GB of memory being available. I have tested both RAM slots by booting with just one slot populated. The laptop will boot with RAM inserted in top slot alone, but not bottom slot alone. Is there an easy way to replace these slots or diagnose the problem?
So, I recently ran into this issue. I scoured the internets and found this odd solution that worked for me: As you know MacBook Pro’s run hotter than your furnace and sometimes can warp their board due to the heat. the bottom ram slot will not register that anything is inserted or will freeze the system and beep 3 times when any ram is inserted on the bottom slot. The solution I found was to LOOSEN the four screws that hold the ram slot in place. Why this works: As the MacBook Pro endures waves of heat over the years the logic board warps causing the screws on the ram slots to tighten casing connection issues on the bottom ram slot. loosening these screws allows the slots to move with the heat and allows the bottom slot to be read. I did this with a Late 2011 13” MacBook Pro that was having 3 beep post memory errors and it worked like a champ! Hasn’t frozen or thrown up the error since!
