2012 MacBook Pro beeps 3 times

If your MacBook Pro is not starting up and giving 3 beeps, it is indicating a RAM (random-access memory) related issue. Here are some steps you can take to try to fix the issue:

1. Reset the RAM: Turn off your MacBook Pro and unplug it from the power source. Open the back cover of your MacBook Pro, remove the RAM modules, and then reseat them firmly in their slots. Make sure that the RAM is properly seated and locked in place.

2. Try with one RAM module at a time: If reseating the RAM modules doesn't work, try removing one RAM module at a time and turning on your MacBook Pro to see if one of the modules is faulty. If your MacBook Pro starts up with only one of the RAM modules installed, then the other module may be faulty.

3. Replace the faulty RAM: If one of the RAM modules is faulty, you'll need to replace it with a new one. Make sure to buy the correct type and size of RAM for your MacBook Pro.

4. Reset the SMC: Resetting the System Management Controller (SMC) can sometimes help fix hardware-related issues. To do this, turn off your MacBook Pro, hold down the Shift + Control + Option keys, and then press and hold the power button for 10 seconds. Release the keys and turn on your MacBook Pro.

Further, you can also check the below link for the steps to be followed in each method above:

https://www.stellarinfo.com/blog/fixed-macbook-beeping-3-times/

If none of these steps work, it may be necessary to take your MacBook Pro to a professional repair service to diagnose and fix the issue.

Hope it helps!

You can use Apple Diagnostics to identify faulty RAM: Use Apple Diagnostics to test your Mac - Apple Support. If that RAM fails diagnostics, replace it. Most reputable memory vendors offer a lifetime guarantee.

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With those older models, the memory slot nearest the Bottom Case can fail due to bad solder joints. You can see if this is the case by powering on the laptop with an Option Boot allowing the laptop to sit at the Apple boot picker menu. Now press on the Bottom Case near the center of the laptop...many times this will trigger the failure if the solder joints are bad (sometimes just moving the laptop can trigger it). If this doesn't show a problem, then remove the bottom case and press on the black plastic base for the memory module slots while the laptop is powered on (sitting at Option boot screen is best so not to corrupt the file system or any data). This will almost always cause a system freeze which may be shown by the pointer not being able to move, or by graphical glitches on the screen.

If that slot is bad, then just remove that memory module and use the laptop with just a single stick of memory.

Just make sure not to allow any metal or conductive item or surface make contact with anything inside the laptop when performing this procedure with the Bottom Case removed.

How long have you had these memory modules installed into this laptop?

What is the make & model of these memory modules? Macs are very picky about the memory used. Are these memory modules listed as "Mac Compatible"?

So if you install one memory module you get the three beeps? This happens for either slot? And you tried each module by itself by filling just one of the slots?

Is the memory module fully latched into place? Sometimes the little triangular protrusion on the locking clips can be worn which can prevent a memory module from being locked into place.

Usually you will only see one memory slot being bad, or one memory module. It is rare that two memory slots or two memory modules will go bad, but I suppose it can happen I've just never seen it while supporting thousands of our organizations computers for decades. If both memory slots are not functional even when testing with know good & Mac compatible memory installed, then there is a problem with the Logic Board.

Be advised Macs do not have the ability to alter their memory bus speed like Windows PCs. That renders testing a Mac's RAM in a PC effectively meaningless.

I'm not at a Mac right now so I can't determine if that RAM is correct for your model Mac or not, but if it is not passing AD (or if AD can't even begin to test it) then it's almost certain not correct for that Mac, or a different problem exists. Whereas a PC can alter its memory bus speed to cope with different RAM speeds, a Mac simply has no way to do that.

Whether that RAM is too fast, too slow, or simply no good is irrelevant. The only practicable way to isolate the problem to the memory, its sockets, the logic board, or something else is to substitute RAM known to function in an identical model Mac.

I cannot see clearly for the second picture showing memory in the slot nearest the keyboard since the edge latches cannot be seen. If one of those protrusions is not able to cover the edge of the memory module, then that module won't be held in place and could easily cause a memory failure.

FYI, there is something red between the contacts of the empty slot in the second photo. Not a problem, but if there is something else there actually on a contact, then it may be a problem.

While the speed looks correct, not certain about the other timings since I've rarely seen them in recent years. I will only purchase memory from Crucial or OWC which tells me the exact part number which is compatible. The days of utilizing the timing values is long gone ....plus Apple does not tell us what those other timings should be. More than likely if you've been using these memory modules for three years, then they are likely compatible, but for me it will still be a possible issue. Nothing against the SK Hynix brand, it is all about the timings being compatible. If this memory was purchased as being guaranteed 100% Mac compatible then it should be fine, but if this memory was purchased just based on the timings, then who knows.

Assuming the memory modules are good since they work in the other computer, then it would seem your Logic Board on this Mac is bad.