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2011年後期モデル番号A1278 / 2.4 GHz i5 or 2.8 GHz i7 プロセッサー

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Lower SO-DIMM RAM slot not working

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?

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Tell us about the RAM you are trying to use.

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The RAM that came with the MAC. Both chips are working, as both will boot from the top slot.

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@Louis Rossmann gave the following answer (which has subsequently been deleted) which I actually found useful (my solution is to max out top slot)! I'll place it as a comment and remove if it is found factually inaccurate.

Bottom slot is soldered using BGA soldering, top slot is soldered using through hole soldering. It is common for the bottom slot to die.

The pads slowly come away from the board or disconnect from internal vias, usually from a drop or from someone soldering near the slots with the RAM still attached. There is no fixing this, just max out the top slot and call it a day, and thank Apple for using BGA for soldering a RAM slot to the motherboard.

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So I bought this i.e. Crucial 8GB DDR3 1333 MT/s CL9 SODIMM 204 Pin 1.35V/1.5V Memory Module for Mac, and it's done the trick. The laptop registers as having 8GB of RAM and runs like a beast once more.

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Thank you James Owers, for posting this here. I have only one slot working, and I will do the fix of running max RAM in the one good slot.

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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!

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James Owers さん、ありがとうございました!
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